Cosmos Portal

The Night Sky: September 2010

The Night Sky in September 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases in Month
New Moon on the 8th Full "Harvest" Moon on the 23rd

Stars and Constellations

The Sun reaches the Autumnal Equinox on September 22 at 11:09 pm, signaling the official end of summer and the beginning of autumn in the Northern Hemisphere. The formal arrival of autumn notwithstanding, the majority of summer stars and even a few spring stars are still well placed for viewing during the early evening hours. By about 9 pm, orange-colored Artcurus in the summer constellation of Boötes (the Herdsman) is low, but still visible, in the west. The Big Dipper, which is really just a portion of the constellation Ursa Major, is low on the northwestern horizon, and so you will not be able to see it if trees or buildings obstruct your view of this part of the sky. The handle of the Dipper arcs to Arcturus.

The famous summer triangle of Vega in Lyra, Deneb in Cygnus, and Altair in Aquila is nearly overhead for a couple of hours after sunset. Orange-red Antares in the Scorpion is quite low in the southwest. You should also be able to find the asterism known as the “teapot” of Sagittarius, just east of Antares. If you are located away from city lights, you may be able to make out the Milky Way as a hazy band stretching across the sky, passing through Sagittarius, Aquila, Lyra, Cygnus, and Cassiopeia. The Milky Way is the galaxy of about 400 billion stars in which our solar system resides, and its nucleus lies in the direction of Sagittarius, but at a distance of 27,000 light years, which is far beyond the mere several hundred light years of the stars which define the constellation Sagittarius. There must be some exotic activity taking place in the core, because as early as 1931 radio engineer Karl Jansky of Bell Labs detected strong radio emissions coming from that region. Astronomers now have evidence that a supermassive black hole of several million solar masses lies at the very center of the Milky Way’s core.

As the stars of summer gradually fade into the evening twilight, the first stars of autumn are appearing in the eastern sky. Making its appearance in the southeast after about 10 pm is the white star Fomalhaut, which lies in the constellation of Pisces Austrinus (the Southern Fish). Rising due east at about this time is the Great Square of Pegasus, four whitish stars in the form of a rectangle (not quite square) lying on its edge. Low in the northeast is the famous “W” shape of the constellation Cassiopeia, the Queen of ancient Ethiopia. Note that the direction in which the “W” opens up is toward Polaris, the North Star.

Naked-Eye Planets In the Evening and Morning Sky

Since early spring, Venus has glimmered like a yellow diamond in the western sky shortly after sunset, and the spectacular evening “star” reaches its peak brightness late this month. Unfortunately, since June Venus has been setting earlier each night, and it now hovers pretty low above the western horizon at dusk. Unless your view in that direction is relatively unobstructed, Venus’s brilliance may go unnoticed. On the 1st, Venus, accompanied by the much fainter true star Spica to its right, sets about an hour and a half after sunset, or 9 pm EDT. By month’s end, Venus sets less than an hour after the Sun, but at this time a telescope will reveal an impressive crescent phase like the Moon’s. Venus will vanish entirely from the evening sky during October, only to reappear prominently in the early morning sky in November.

Mars spends September in the vicinity of Venus in Virgo. Both planets stand low in the west after sunset, but while Venus needs no optical aid to see, it will help to use binoculars to locate the much fainter Mars, which will resemble an orange star. During September, Mars sets roughly one and a half hours after sunset, or at 9 pm on the 1st and 8 pm on the 30th. Saturn, like Venus and Mars, is located in Virgo, but in the eastern portion of that constellation nearer to the Sun’s position and therefore difficult to pick out in the Sun’s glare. Saturn will vanish into the twilight by the end of September.

Jupiter reaches opposition with the Sun on the 21st, and is therefore visible all night long. Now at its closest to Earth, Jupiter sparkles like a brilliant cream-colored star in the dim constellation Pisces; it outshines everything in the night sky except for the Moon and Venus. Jupiter is a magnificent sight in a telescope, revealing cloud bands and (at the right moment) the Great Red Spot in its atmosphere and four Galilean moons surrounding the planet’s globe.

Mercury is too close to the Sun to be viewed in early September, but by midmonth Mercury begins to appear as a “morning star” low in the east at dawn. At its best, on the 19th, Mercury rises only about 90 minutes before the Sun. To spot it, one should look about a half-hour before sunrise, but it may be a challenge to spot Mercury against the bright twilight.

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky: September 2010

The Night Sky in September 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases in Month
New Moon on the 8th Full "Harvest" Moon on the 23rd

Stars and Constellations

Naked-Eye Planets In the Evening and Morning Sky

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky: August 2010

The Night Sky in August 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases in Month
New Moon on the 9th Full "Sturgeon" Moon on the 24th

Stars and Constellations

As night falls on clear August evenings, the first star to emerge is orange-yellow Arcturus, which stands high in the west about an hour or so after sunset. Arcturus, is an orange giant star lying 37 light years away from our solar system. This identification can be verified once it gets truly dark by first locating the Big Dipper, a part of the constellation Ursa Major, which is now dipping into the northwest. The two front stars in the bowl of the Big Dipper, Dubhe and Merak, point to Polaris, the North Star, while the arc of the Big Dipper’s handle leads to Arcturus. If the sky is dark enough, you may be able to see the Little Dipper, which is part of Ursa Minor, extending outward from Polaris toward the upper left.

One large, but faint summer constellation is Draco, the Dragon, which winds across the sky high above the Little Dipper. The Dragon’s head lies in the vicinity of Vega and its tail is near Dubhe. Draco is circumpolar for most US residents, meaning that its stars never set, but simply revolve around Polaris during the night. Draco is perhaps most notable because one of its stars, alpha Draconis, or Thuban, was the polestar some 4000 years ago, as was described in this column last August. The brightest star in Draco, gamma Draconis, or Eltamin, is an orange giant star similar to Arcturus but lying about four times farther away. Eltamin’s claim to astronomical fame is that it was used by English astronomer James Bradley in 1728 to measure a phenomenon of light known as aberration. The phenomenon has an analog in ordinary experience – as you walk through a light rainfall, the raindrops appear to be coming at you, and so you need to tilt your umbrella forward slightly. Similarly, starlight incident on planet Earth as it revolves about the Sun at a speed of 30 kilometers per second appears to be coming from a slightly different direction than it really is, and consequently, over the course of an entire year, the star itself appears to trace out a tiny elliptical path in the sky. This effect is a direct result of the finite velocity of light, and also serves as a demonstration of the Earth’s orbit about the Sun.

Try to get one last glimpse of the spring star Spica as it sets in the southwest. To the far left of Spica is orange-red Antares in Scorpius, the Scorpion, which is visible low in the south-southwest. The body of the Scorpion snakes down toward the horizon and then upward into a curved stinger. Look closely, and you will be able to see the “cat’s eyes,” Shaula and Lesath, a pair of stars located at the end of the tail which seem to be winking at you. To the upper left of the cat’s eyes is the “teapot” of Sagittarius, which marks the general direction of the core of our Milky Way galaxy. If you live away from city lights, you can make out the Milky Way as a hazy band stretching across the sky from southwest to northeast. In fact it passes through the region of the summer triangle, which at this time stands high in the east-northeast. The triangle is comprised of Vega in the constellation Lyra, Deneb in Cygnus, and Altair in Aquila. All three stars of the summer triangle are whitish in color, indicating that they are all somewhat hotter than our Sun.

Late in the evening the Great Square of Pegasus, which consists of four stars in the form of a rectangle lying on its edge, can be seen rising in the east. You should also be able to distinguish the “W” shape of Cassiopeia as it rises low in the northeast. When you see these two celestial signs, autumn is surely just around the corner!

Naked-Eye Planets In the Evening and Morning Sky

All five of the naked-eye planets are up in the evening sky this August. Mercury begins the month as an evening “star,” located low in the west at dusk. Your best bet to find it is to look about a half-hour after sunset, but be aware that you will need a western horizon unobstructed by trees or houses, and even so it will be difficult to spot Mercury against the bright evening twilight. Mercury sets about an hour after the Sun during the first week of August, and vanishes into the twilight afterwards.

In contrast to Mercury, Venus is a spectacular evening “star,” scintillating like a yellow diamond in the west at dusk. Venus actually brightens over the month of August, as the distance between it and Earth decreases. At the same time, Venus sets earlier each night: two hours after sunset, or about 10 pm EDT, at the beginning of August, but an hour and a half after the Sun by month’s end. Venus races through Virgo during August, passing Saturn on the 7th, Mars on the 18th, and the star Spica on the 31st.

Mars and Saturn begin the month of August together in the western part of Virgo, where Saturn shines like a yellow star, distinctly brighter than orange Mars, and comparable with blue-white Spica further to the east. During the course of the month, Mars continues to track eastward through Virgo, leaving Saturn behind. But Venus is moving faster than either of them, and by the end of the first week of August, the three planets are close enough to form a beautiful, though unequal, trio. During August, Mars and Saturn set, respectively, around 10 pm and 9:30 pm at midmonth. Mars will remain an evening planet (albeit a faint one) through autumn, while Saturn will vanish into the twilight by late September and reappear in the morning sky in October.

Jupiter stands out like a brilliant cream-colored star in the dim constellation Pisces, outshining everything in the night sky except the Moon and Venus. Jupiter currently lies diametrically opposite in the sky to its fellow giant planet Saturn (and also Mars and Venus), so that Jupiter rises in the east at about the same time as Saturn sets in the west, which is around 9:30 pm at midmonth. Jupiter is truly a magnificent sight in even a small telescope, revealing cloud bands and (at the right moment) the Great Red Spot in its atmosphere and four Galilean moons surrounding the planet’s globe.

Earth passes through the debris of Comet Swift-Tuttle on August 11-12, producing a meteor shower. Meteors should become visible in late evening, with the best show occurring after midnight. Look generally in the northeast direction, but meteors can be seen in any part of the sky.

Some content for this article has been obtained from the US Naval Observatory Data Services. Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

The Night Sky: July 2010

The Night Sky in July 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases in Month
New Moon on the 11th Full "Thunder" Moon on the 25th

Stars and Constellations

July evenings present significant challenges for stargazing, not only because they are often hazy but also since you have to wait until after 9 pm for the sky to become dark enough to make out the constellation patterns. As twilight fades into night, you should still be able to spot a few of the bright stars of spring before they vanish into the evening twilight. Blue-white Regulus in Leo is moving toward the western horizon and sets around 10 pm in mid-July, followed a couple of hours later by similarly colored Spica in Virgo. The brightest of the visible stars is orange Arcturus, in the constellation Boötes , which is high in the south during the early evening hours. Although it is considered a star of spring, Arcturus will remain in view until early autumn. Arcturus, Regulus, and Spica form the Spring Triangle, and July is the last month to catch a glimpse of it until it reappears in the morning sky next year.

As this trio of spring stars is setting in the west, another trio of summer stars is rising in the northeast. Making their appearance above the eastern horizon are Vega, Deneb, and Altair, located respectively in the constellations Lyra, Cygnus, and Aquila. These three stars comprise the famous Summer Triangle, which, though smaller in sky area than its spring counterpart, is more famous.

Located between the constellations Boötes and Lyra is Hercules, which is identified by its “keystone” of four stars. Perhaps the most notable star in Hercules is Ras Algethi (Arabic for the “Kneeler’s Head”), a supergiant star with a diameter of several hundred times that of the Sun and lying about 400 light years from the Sun. In 1783, English astronomer William Herschel determined, from a careful study of star motions, that our entire solar system is traveling through our Galaxy, the Milky Way, and headed toward a point in Hercules known as the apex of solar motion. Modern analyses have since shown that the apex lies closer to Vega in Lyra, but Herschel’s studies were nevertheless ground-breaking for astronomy.

Moving into view in the south-southeast in early evening is reddish Antares in the constellation Scorpius. Antares is a red supergiant and one of the largest stars known, having a diameter nearly 800 times larger than the Sun, and lying over 600 light years from our solar system. A little later in the evening, the constellation Sagittarius, with its famous “Teapot” asterism will be rising in the southeast, to the left of Antares.

Located directly above Scorpius and below Hercules is Ophiuchus, the Serpent Bearer. Its brightest star, Ras Alhague (translated as “Head of the Serpent Holder”) lies just a few degrees to the east of Ras Algethi in Hercules. Curiously, though, the most celebrated star in Ophiuchus is too faint to see with the unaided eye. That star is Barnard’s Star, a faint red dwarf discovered in 1916 by astronomer Edward Emerson Barnard at the Yerkes Observatory in Wisconsin. By comparing photographic plates taken decades apart, Barnard ascertained that the star is moving rapidly across the sky, a sure indication that it is nearby. Parallax studies have shown that Barnard’s star is 6 light years from our solar system, making it the second closest star after the Alpha Centauri triple system. Barnard’s star is also much redder and fainter than the Sun, with one-fifth its diameter, or about twice that of the planet Jupiter. Due to its swift motion across the sky, Barnard star’s will in several thousand years migrate from Ophiuchus into Hercules.

Naked-Eye Planets In the Evening and Morning Sky

Mercury begins to appear above the western horizon during July, and sets about an hour after the Sun for most of the month, but it will be quite low and difficult to spot against the bright evening twilight. Toward the end of July, Mercury passes close to Regulus, and the pair should be easily visible in binoculars. Much brighter Venus maintains its dominance in the evening sky, sparkling like a yellow gem in the west at dusk. Venus has actually been gradually increasing in brightness over the past few weeks, a trend that will continue into early autumn as Venus’s orbital motion brings it closer to Earth. But Venus will also be slowly and inexorably sinking toward the western horizon. Venus sets two and a half hours after sunset (about 11 pm EDT) at the beginning of July, but only two hours after the Sun by month’s end, at which time a telescope will reveal a nearly “quarter phase.” During the second week in July, Venus passes just above Regulus, making for a lovely sight in binoculars. The apparent proximity is, of course, a consequence of perspective, since Regulus is 15 million times farther away than Venus!

Mars, mimicking a bright orange star in the eastern part of Leo as July opens, continues its eastward motion, eventually migrating into Virgo and, at month’s end, meeting up with Saturn. Mars’s brightness has now faded to about the same as that of Regulus, which it passed close to last month. During July, Mars remains in view until late evening, setting around 11 pm at midmonth. To the east of Mars is Saturn, which resembles a bright yellow star roughly halfway between the true stars Regulus and Spica. Saturn’s brightness has diminished to where it is now comparable with that of Spica, Regulus, and Mars. At the end of July, Mars will pass just below Saturn, making for a pretty sight in binoculars or a small telescope. Saturn remains in good position for viewing during the early evening hours of July, setting around 12:30 am on the 1st and by 10:30 am on the 31st.

As Saturn and Mars are setting in the west, Jupiter is rising in the east. Jupiter, resembling a brilliant cream-colored star in the faint constellation Pisces, is second only to Venus in brightness among the planets. This July, Jupiter moves into the evening sky, rising by 11:30 pm at mid-month.

Planet Earth reaches aphelion, or its farthest distance in its elliptical orbit from the Sun, on July 6. Note that it is the tilt of Earth’s axis, not its orbital shape, which causes the changing seasons.

For more information on astronomy and weather, visit the Widener University Public Viewing Website at http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

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The Night Sky: June 2010

The Night Sky in June 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 12thFull "Strawberry Moon" on 26th

Stars and Constellations

Although summer officially begins this month, the stars of spring are still viewable during the early evening, including blue-white Regulus in the constellation Leo. Regulus stands high in the southwest in early evening, and sets around midnight. A star with similar color and brightness is Spica, which stands about halfway up in the south shortly after nightfall. But the first true star to be spotted through the evening twilight is Arcturus, the fourth brightest star in the entire sky, in the constellation of Boötes, the Herdsman. Arcturus has a distinct yellow-orange color, and lies high above Spica in the south at around 9 pm EDT. To find Arcturus and Spica, first locate the Big Dipper, and follow the arc of the Dipper’s handle outward until you encounter Arcturus, then continue on to meet Spica.

To the east of Virgo is the next zodiac constellation Libra (the Scales). Its two brightest stars are Zubenelgenubi and Zubeneschamali, the latter of which appears to have a greenish tinge when seen through a telescope. If the sky is especially dark where you live, try to locate the semicircle of stars representing the constellation Corona Borealis (Northern Crown) just a bit above and to the east of Arcturus. In mythology, Corona Borealis represented the crown of Princess Ariadne, daughter of King Minos of Crete. The crown’s brightest star is blue-white Alphekka, also known as Gemma. To the east of Corona Borealis is Hercules, the fifth largest constellation in the sky. The brightest star in Hercules is Rasalgethi, which is both a variable star and a double star.

One of the least known spring constellations is Canes Venatici (Hunting Dogs), which passes nearly overhead in the early evening hours of June. This tiny group was originally part of Ursa Major, but in 1690 Johannes Hevelius introduced it to represent a faithful pair of dogs to accompany Boötes. Canes Venatici contains only one relatively bright star, Alpha Canum Venaticorum, better known as Cor Caroli, or "Heart of Charles." The name may have been bestowed by Edmond Halley in the late 1600s in honor of his king, Charles II. When viewed through a telescope, Cor Caroli is revealed to be a splendid double star, with the brighter component blue and the fainter one yellow. The blue star is peculiar, showing evidence of a powerful magnetic field. Cor Carolis is important enough to be listed in astronomer Dr. James Kaler’s book, The Hundred Greatest Stars (New York: Copernicus Books, 2002). The system lies about 110 light years from our solar system.

Each June the Sun passes in front of the stars of Taurus and Gemini, and so these constellations are too overwhelmed by solar glare to be seen at this time of year. The Sun reaches the solstice point on the 21st at 7:28 am, when the North Pole of Earth is tilted maximally toward the Sun, marking the beginning of summer in the Northern Hemisphere.

Naked-Eye Planets In the Evening and Morning Sky

Venus easily outshines all the other planets. It sparkles like a yellow diamond in the west-northwest during the early evening hours. Throughout June, Venus sets roughly two and a half hours after sunset, or at 11 pm EDT, which is about as late as it can set. Mars begins the month just to the west of Regulus, but it is moving steadily eastward, and passes just above Regulus on the 7th. By month’s end Mars stands well to the east of Regulus. The color contrast between the orange planet and the blue-white star is quite striking. Mars remains in view until after midnight for most of the month, setting around 1 am on the 1st and by about 11:30 pm on the 30th.

Saturn continues to inhabit the constellation Virgo near its western border with Leo. Saturn resembles a yellow star situated between the blue-white true stars Regulus to its right and Spica to its left. Both Mars and Saturn have been steadily diminishing in brightness since their respective oppositions with the Sun back in January and March, although Mars has faded more dramatically and is now slightly fainter than Saturn. Saturn remains in good position for viewing for the entire month of June, setting around 2:30 am on the 1st and by 12:30 am at month’s end.

Situated in the early morning sky, Jupiter rises by 2:30 am as June begins and around 12:30 am as the month closes. After Jupiter has cleared the horizon, it looks like an extremely bright cream-colored star hovering low in the eastern sky. Also in the morning, Mercury rises about an hour before sunrise as June begins, but it will be quite a challenge to spot it against the glare of the dawn twilight. Moreover, if your eastern horizon is obstructed by houses or trees, you will have little hope of seeing Mercury. Toward the end of the month, Mercury sinks toward the morning twilight, and reaches superior conjunction with the Sun (i.e., Mercury lies on the opposite side of the Sun from Earth) on the 28th; it will reappear in the evening sky a few days afterwards.

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

The Night Sky: May 2010

The Night Sky in May 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 13thFull "Flower Moon" on 27th

Stars and Constellations

Starlit nights in May are often pleasantly cool, with just a light jacket required for outdoor viewing. But with the Sun setting around 8 pm or later during the month, you will need to wait until close to 9 pm for the sky to get dark enough to make out the constellations. Get a last look at Aldebaran and the Pleiades star cluster, Rigel and Betelgeuse, Pollux and Castor, and Sirius and Procyon. Bright yellow Capella is setting in the northwest, but will still be visible through June. These bright stars of winter are all fading into the evening twilight, not to reappear in the night sky until autumn.

The celestial stage now belongs to the stars of spring. Regulus in Leo is high in the southeast, and another fairly bright star, Alphard, in the constellation Hydra, the Water Snake, is now rising, a bit below Regulus. If you wait until after 10 pm, you will see yet another bright star, Spica, in the constellation Virgo, rising in the southeast. The Big Dipper, which is part of the constellation Ursa Major, is now rising in the northeast, and its famous "pointer stars" point to Polaris, the North Star. The handle of the Dipper arcs to Arcturus, the bright yellow-orange star in the constellation Boötes, the Herdsman, which is rising in the east. Mizar, the second star from the end of the Big Dipper’s handle, is actually a multiple system. As a test of vision, see if you can spot Mizar’s faint companion star, Alcor.

One of the largest and most spectacular constellations in the night sky at this time of year is Centaurus (Chiron in Greek mythology) but only the uppermost portions of this group can be glimpsed from latitudes north of the Gulf Coast states. Centaurus lies just below the tail end of Hydra, and skims the southern horizon around midnight in May. Like Orion, Centaurus boasts two first-magnitude stars: alpha and beta Centauri. Alpha Centauri, also known as Rigel Kentaurus, is a triple-star system, and has the distinction of being our Sun’s nearest stellar neighbor, at a distance of 4.3 light years. Even more interesting is that the brightest of the three components, alpha Centauri A, is nearly identical in chemical composition and intrinsic brightness to the Sun. Beta Centauri, by contrast, is a blue-white giant star many times larger than the Sun and it lies much farther away than alpha, around 200 light years. If your travels take you to Mexico, Hawaii, or, even better, South America, southern Africa, Australia, or New Zealand, watch for brilliant Centaurus in the night sky in May.

Naked-Eye Planets In the Evening and Morning Sky

There is no mistaking the planet Venus, which looks like a magnificent yellow diamond hovering above the western horizon during the early evening hours of May. Throughout the entire month, Venus remains visible during the evening for a generous amount of time, setting around two and a half hours after sunset, or at about 10:15 pm EDT on the 1st and by 11 pm on the 31st.

Mars continues to shine like a bright, copper-colored star just to the west of Regulus in Leo. Mars remains in view until well after midnight, setting around 2:30 am on the 1st and by about 1 am on the 31st. Mars’ distance from Earth has more than doubled since its opposition with the Sun back in January, and its brightness has faded by nearly a factor of ten. Saturn, now located in the western part of the constellation Virgo, near the border with Leo, resembles a yellow star situated roughly between the (true) blue-white stars Regulus to its upper right and Spica to its lower left. Saturn’s brightness has faded since its opposition with the Sun back in March, and it is now about equal with that of nearby Mars. Saturn remains in good position for viewing for nearly the entire month of May, setting during the very early hours of morning.

Jupiter begins to emerge from the dawn twilight during May, rising about 4 am EDT (roughly two hours before sunrise) at the beginning of the month and by 2:30 am on the 31st. Allow Jupiter an hour or so to clear the horizon after it rises, and you will easily spot it looking like a bright cream-colored star. Mercury reached inferior conjunction with the Sun late last month, and is therefore be unobservable until very late in May, when it appears low above the eastern horizon before the Sun rises. Mercury reaches greatest elongation on the 26th, rising about an hour before sunrise, but it will be a challenge to spot it against the glare of the dawn sky.

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

Astronomers See Historical Supernova From a New Angle

CAMBRIDGE, MA (April 7, 2010) – Since Galileo first pointed a telescope at the sky 400 years ago, a myriad of technological advances have allowed astronomers to look at very faint objects, very distant objects, and even light that's invisible to the human eye. Yet, one aspect usually remains out of reach - the benefit of a 3-D perspective.

Our telescopes show the Milky Way galaxy only as it appears from one vantage point: our solar system. Now, using a simple but powerful technique, a group of astronomers led by Armin Rest of Harvard University has seen an exploding star or supernova from several angles. "The same event looks different from different places in the Milky Way," said Rest. "For the first time, we can see a supernova from an alien perspective."

The supernova left behind the gaseous remnant Cassiopeia A. The supernova's light washed over the Earth about 330 years ago. But light that took a longer path, reflecting off clouds of interstellar dust, is just now reaching us. This faint, reflected light is what the astronomers have detected.

The technique is based on the familiar concept of an echo, but applied to light instead of sound. If you yell, "Echo!" in a cave, sound waves bounce off the walls and reflect back to your ears, creating echoes. Similarly, light from the supernova reflects off interstellar dust to the Earth. The dust cloud acts like a mirror, creating light echoes that come from different directions depending on where the clouds are located.

"Just like mirrors in a changing room show you a clothing outfit from all sides, interstellar dust clouds act like mirrors to show us different sides of the supernova," explained Rest.

Moreover, an audible echo is delayed since it takes time for the sound waves to bounce around the cave and back. Light echoes also are delayed by the time it takes for light to travel to the dust and reflect back. As a result, light echoing from the supernova can reach us hundreds of years after the supernova itself has faded away.

Not only do light echoes give astronomers a chance to directly study historical supernovae, they also provide a 3-D perspective since each echo comes from a spot with a different view of the explosion.

Most people think a supernova is like a powerful fireworks blast, expanding outward in a round shell that looks the same from every angle. But by studying the light echoes, the team discovered that one direction in particular looked significantly different than the others.

They found signs of gas from the stellar explosion streaming toward one point at a speed almost 9 million miles per hour (2,500 miles per second) faster than any other observed direction.

"This supernova was two-faced!" said Smithsonian co-author and Clay Fellow Ryan Foley. "In one direction the exploding star was blasted to a much higher speed."

Previous studies support the team's finding. For example, the neutron star created when the star's core collapsed is zooming through space at nearly 800,000 miles per hour in a direction opposite the unique light echo. The explosion may have kicked gas one way and the neutron star out the other side (a consequence of Newton's third law of motion, which states that every action has an equal and opposite reaction).

By combining the new light-echo measurements and the movement of the neutron star with X-ray data on the supernova remnant, astronomers have assembled a 3-D perspective, giving them new insight into the Cas A supernova.

"Now we can connect the dots from the explosion itself, to the supernova's light, to the supernova remnant," said Foley.

Cassiopeia A is located about 16,000 light-years from Earth and contains matter at temperatures of around 50 million degrees F, causing it to glow in X-rays. A 3-D computer model of the remnant is online.

The Mayall 4-meter telescope at Kitt Peak National Observatory was used to locate the light echoes. Follow-up spectra were obtained with the 10-meter Keck I Telescope.

The journal paper describing this discovery is available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Triton’s Summer Sky of Methane and Carbon Monoxide

GARCHING, Germany (April 6, 2010) – According to the first ever infrared analysis of the atmosphere of Neptune's moon Triton, summer is in full swing in its southern hemisphere. The European observing team used ESO's Very Large Telescope and discovered carbon monoxide and made the first ground-based detection of methane in Triton's thin atmosphere. These observations revealed that the thin atmosphere varies seasonally, thickening when warmed.

"We have found real evidence that the Sun still makes its presence felt on Triton, even from so far away. This icy moon actually has seasons just as we do on Earth, but they change far more slowly," says Emmanuel Lellouch, the lead author of the paper reporting these results in Astronomy & Astrophysics.

On Triton, where the average surface temperature is about minus 235 degrees Celsius, it is currently summer in the southern hemisphere and winter in the northern. As Triton's southern hemisphere warms up, a thin layer of frozen nitrogen, methane, and carbon monoxide on Triton's surface sublimates into gas, thickening the icy atmosphere as the season progresses during Neptune's 165-year orbit around the Sun. A season on Triton lasts a little over 40 years, and Triton passed the southern summer solstice in 2000.

Based on the amount of gas measured, Lellouch and his colleagues estimate that Triton's atmospheric pressure may have risen by a factor of four compared to the measurements made by Voyager 2 in 1989, when it was still spring on the giant moon. The atmospheric pressure on Triton is now between 40 and 65 microbars — 20 000 times less than on Earth.

Carbon monoxide was known to be present as ice on the surface, but Lellouch and his team discovered that Triton's upper surface layer is enriched with carbon monoxide ice by about a factor of ten compared to the deeper layers, and that it is this upper "film" that feeds the atmosphere. While the majority of Triton’s atmosphere is nitrogen (much like on Earth), the methane in the atmosphere, first detected by Voyager 2, and only now confirmed in this study from Earth, plays an important role as well. "Climate and atmospheric models of Triton have to be revisited now, now that we have found carbon monoxide and re-measured the methane," says co-author Catherine de Bergh.

Of Neptune's 13 moons, Triton is by far the largest, and, at 2700 kilometres in diameter (or three quarters the Earth’s Moon), is the seventh largest moon in the whole Solar System. Since its discovery in 1846, Triton has fascinated astronomers thanks to its geologic activity, the many different types of surface ices, such as frozen nitrogen as well as water and dry ice (frozen carbon dioxide), and its unique retrograde motion [1].

Observing the atmosphere of Triton, which is roughly 30 times further from the Sun than Earth, is not easy. In the 1980s, astronomers theorised that the atmosphere on Neptune's moon might be as thick as that of Mars (7 millibars). It wasn't until Voyager 2 passed the planet in 1989 that the atmosphere of nitrogen and methane, at an actual pressure of 14 microbars, 70 000 times less dense than the atmosphere on Earth, was measured. Since then, ground-based observations have been limited. Observations of stellar occultations (a phenomenon that occurs when a Solar System body passes in front of a star and blocks its light) indicated that Triton’s surface pressure was increasing in the 1990's. It took the development of the Cryogenic High-Resolution Infrared Echelle Spectrograph (CRIRES) at the Very Large Telescope (VLT) to provide the team the chance to perform a far more detailed study of Triton’s atmosphere. "We needed the sensitivity and capability of CRIRES to take very detailed spectra to look at the very tenuous atmosphere," says co-author Ulli Käufl. The observations are part of a campaign that also includes a study of Pluto [eso0908].

Pluto, often considered a cousin of Triton and with similar conditions, is receiving renewed interest in the light of the carbon monoxide discovery, and astronomers are racing to find this chemical on the even more distant dwarf planet.

This is just the first step for astronomers using CRIRES to understand the physics of distant bodies in the Solar System. "We can now start monitoring the atmosphere and learn a lot about the seasonal evolution of Triton over decades," Lellouch says.

Notes

[1] Triton is the only large moon in the Solar System with a retrograde motion, which is a motion in the opposite direction to its planet's rotation. This is one of the reasons why Triton is thought to have been captured from the Kuiper Belt, and thus shares many features with the dwarf planets, such as Pluto.

More information

This research was presented in a paper to appear in Astronomy & Astrophysics (“Detection of CO in Triton’s atmosphere and the nature of surface-atmosphere interactions”, by E. Lellouch et al.), reference DOI : 10.1051/0004-6361/201014339.

The team is composed of E. Lellouch, C. de Bergh, B. Sicardy (LESIA, Observatoire de Paris, France), S. Ferron (ACRI-ST, Sophia-Antipolis, France), and H.-U. Käufl (ESO).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Contacts

Emmanuel Lellouch
LESIA, Observatoire de Paris
France
Tel: +33 1 450 77 672
Email: emmanuel.lellouch@obspm.fr

Hans-Ulrich Käufl
ESO
Garching, Germany
Tel: +49 89 3200 6414
Cell: +49 160 636 5135
Email: hukaufl@eso.org

Henri Boffin
ESO - VLT Press Officer
Garching, Germany
Tel: +49 89 3200 6222
Cell: +49 174 515 43 24
Email: hboffin@eso.org

Is Our Universe at Home Within a Larger Universe?

BLOOMINGTON, Ind. (April 5, 2010) – Could our universe be located within the interior of a wormhole which itself is part of a black hole that lies within a much larger universe?

Such a scenario in which the universe is born from inside a wormhole (also called an Einstein-Rosen Bridge) is suggested in a paper from Indiana University theoretical physicist Nikodem Poplawski in Physics Letters B. The final version of the paper was available online March 29 and will be published in the journal edition April 12.

FIGURE CAPTION –– Einstein-Rosen bridges like the one visualized above have never been observed in nature, but they provide theoretical physicists and cosmologists with solutions in general relativity by combining models of black holes and white holes.

Poplawski takes advantage of the Euclidean-based coordinate system called isotropic coordinates to describe the gravitational field of a black hole and to model the radial geodesic motion of a massive particle into a black hole.

In studying the radial motion through the event horizon (a black hole's boundary) of two different types of black holes -- Schwarzschild and Einstein-Rosen, both of which are mathematically legitimate solutions of general relativity -- Poplawski admits that only experiment or observation can reveal the motion of a particle falling into an actual black hole. But he also notes that since observers can only see the outside of the black hole, the interior cannot be observed unless an observer enters or resides within.

"This condition would be satisfied if our universe were the interior of a black hole existing in a bigger universe," he said. "Because Einstein's general theory of relativity does not choose a time orientation, if a black hole can form from the gravitational collapse of matter through an event horizon in the future then the reverse process is also possible. Such a process would describe an exploding white hole: matter emerging from an event horizon in the past, like the expanding universe."

A white hole is connected to a black hole by an Einstein-Rosen bridge (wormhole) and is hypothetically the time reversal of a black hole. Poplawski's paper suggests that all astrophysical black holes, not just Schwarzschild and Einstein-Rosen black holes, may have Einstein-Rosen bridges, each with a new universe inside that formed simultaneously with the black hole.

"From that it follows that our universe could have itself formed from inside a black hole existing inside another universe," he said.

By continuing to study the gravitational collapse of a sphere of dust in isotropic coordinates, and by applying the current research to other types of black holes, views where the universe is born from the interior of an Einstein-Rosen black hole could avoid problems seen by scientists with the Big Bang theory and the black hole information loss problem which claims all information about matter is lost as it goes over the event horizon (in turn defying the laws of quantum physics).

This model in isotropic coordinates of the universe as a black hole could explain the origin of cosmic inflation, Poplawski theorizes.

Poplawski is a research associate in the IU Department of Physics. He holds an M.S. and a Ph.D. in physics from Indiana University and a M.S. in astronomy from the University of Warsaw, Poland.

To speak with Poplawski, please contact Steve Chaplin, University Communications, at 812-856-1896 or stjchap@indiana.edu.

"Radial motion into an Einstein-Rosen bridge," Physics Letters B, by Nikodem J. Poplawski. (Volume 687, Issues 2-3, 12 April 2010, Pages 110-113.

The Night Sky: April 2010

The Night Sky in April 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 14thFull "Pink Moon" on the 28th

Stars and Constellations

The month of April bids farewell to many of the winter stars as they gradually disappear from view in the evening sky. Aldebaran in Taurus and the nearby Pleiades cluster are now setting in the west, and will not reappear until next autumn. Betelgeuse and Rigel in Orion are in the southwestern sky, while the twin stars Pollux and Castor in Gemini are high in the south-southwest, to Orion’s upper left. Blue-white Sirius in Canis Major and Procyon in Canis Minor also follow Orion. The yellow star Capella, in Auriga, is now high in the northwest.

While the stars of winter make their leisurely exit, the stars of spring are taking center stage. Regulus in Leo (the Lion) is high in the southeast, and another moderately bright star, Alphard, in the constellation Hydra (the Water Snake), is now rising, a bit below Regulus. Hydra is the largest of the 88 modern constellations, and represents a nine-headed monster which Hercules battled as one of his labors. The name Alphard means the “solitary one,” which makes sense because Alphard is situated in a region of the sky with almost no other nearby stars of comparable brightness. Alphard is an orange giant star, similar to Arcturus, but about five times further from our solar system, and so it appears noticeably fainter, comparable in apparent brightness to Polaris.

If you wait until after around 10 pm, you will see yet another bright star, Spica, in the constellation Virgo, rising in the southeast following the planet Saturn. The constellation Virgo is especially noteworthy telescopically because it contains over 2000 galaxies, including the famous Virgo Cluster of Galaxies, which is about 55 million light years away. Our own Milky Way and most of the galaxies in its vicinity are gravitationally bound to this cluster.

The Big Dipper, a part of the constellation Ursa Major, is now rising in the northeast, and its handle “arcs” to Arcturus, the bright yellow-orange star in the constellation Boötes (the Herdsman), which is rising in the east. Arcturus lies about 37 light years from our solar system, and has a diameter over 30 times larger than that of our Sun. Arcturus, Spica, and Regulus form a “Spring Triangle” which is larger though not as famous as its summer counterpart.

Naked-Eye Planets In the Evening and Morning Sky

Mercury is at its best in early April this year, reaching greatest evening elongation on the 8th. Look for Mercury around this date, shining like a yellow star in the west after sunset. On this date, Mercury sets about one and a half hours after sunset. Toward the end of the month, however, Mercury sinks rapidly into the western sky, getting closer to the Sun. On the 28th it reaches inferior conjunction with the Sun., and is therefore not observable.

Venus looks like a glittering yellow diamond floating above the western horizon about a half-hour after sunset, and getting higher with each passing night. As April opens, Venus sets around 9 pm EDT, or an hour and a half after sunset. By the 31st, Venus has extended its duration after sunset to just under two and a half hours, setting a little after 10 pm. During the first week of April, brilliant Venus and much fainter Mercury appear close together low in the sky at dusk.

Mars resembles a bright, copper-colored star just to the east of Pollux and Castor in Gemini. Mars stands nearly overhead during the early evening hours of April, remaining in view until well after midnight. Mars sets around 3 pm at midmonth. Mars remains quite bright during April, though it slowly fades all month. Mars has about the same brightness as the nearby star Capella on the 1st, and about the same as Betelgeuse on the 30th.

Saturn, continuing its residence in Virgo, is situated roughly between the true stars Regulus and Spica. Saturn resembles a bright yellow star as it rises above the eastern horizon in early evening. Saturn was in opposition with the Sun last month, and so it remains in fine position for viewing for the entire month of April, setting around 5 am at midmonth.

Jupiter, which was in conjunction with the Sun back in late February, is too close to the Sun to be easily seen until late April, when it sets about one and a half hours before sunrise. Look for what appears to be a bright star hovering above the eastern horizon about 45 minutes before sunrise.

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

The Night Sky: March 2010

The Night Sky in March 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 15thFull "Worm Moon" on the 28th

Stars and Constellations

Spring begins in the Northern Hemisphere on March 20^th at 1:32 pm Eastern Daylight Time, when the noon Sun stands exactly overhead at the Earth’s equator. Although not directly visible because of the Sun's daytime brilliance, the Sun begins March in the constellation (not the astrological sign) Aquarius, crosses into Pisces at mid-month, and remains in Pisces for the remainder of the month. Both Aquarius and Pisces are, of course, autumn constellations, and therefore best viewed at night at the opposite time of the year when the Sun passes through them.

The seasonal transition between winter and spring becomes apparent in the star patterns visible in the night sky as well, for the constellations of winter will over the next several weeks be fading into the evening twilight. The star Aldebaran in Taurus and the compact star cluster Pleiades, or 7 Sisters, are still on display high in the southwest. Just west of overhead is the yellow star Capella, and Betelgeuse and Rigel in Orion are high in the south-southwest. The twin stars Pollux and Castor in the constellation Gemini are high in the southeast, while the brightest appearing star in the night sky, Sirius in Canis Major, shines with bluish-white radiance to Orion’s lower left. Above and to the left of Sirius is Procyon in Canis Minor.

As evening progresses into night, the stars of spring begin to emerge from the eastern horizon. Regulus, the brightest star in Leo, stands high in the east by 9 pm, and is one of the first spring stars to become visible after dark. Regulus lies about 78 light years from our solar system, and is intrinsically 100 times brighter than the Sun. The name Regulus denotes "Royal," and, according to British astronomer Patrick Moore in his book, The Observer’s Year (London: Springer-Verlag, 1998), Regulus was one of the four Royal Stars (along with Aldebaran, Fomalhaut, and Antares) of the ancient Persian monarchy who were "Guardians of the Heavens." Regulus marks the lower part of what is Leo’s most distinctive feature: its "sickle," which represents the mane of the lion. In mythology, Leo represented the Nemean Lion which was slain as one of Hercules' 12 labors. Leo is, of course, one of the twelve zodiac constellations, with the Sun passing within its borders between August 10 and September 15. In fact, Regulus is so close to the ecliptic path that it is occasionally occulted (eclipsed) by the Moon.

But the brightest star in the spring sky is yellow-orange Arcturus in the constellation Boötes (the Herdsman), which can now be glimpsed low in the northeast. Arcturus is the 4th brightest star in the night sky and, like Regulus, is intrinsically about 100 times as luminous as the Sun. However, Arcturus lies 36 light years from our solar system, or about twice as close to us as Regulus, and so it appears brighter. The Big Dipper, which is part of the large constellation Ursa Major, is also rising in the northeast, and its handle arcs to Arcturus. The two front stars in the bowl of the Big Dipper, Merak and Dubhe, point toward the North Star, Polaris.

Naked-Eye Planets In the Evening and Morning Sky

Mercury passes through superior conjunction with the Sun on March 14th and therefore is unobservable for much of March. Toward the end of the month, however, Mercury pops up in the western sky at dusk, and by the 31st it sets nearly one and a half hours after sunset. Venus, which was in conjunction with the Sun back in January, is just beginning to emerge from the evening twilight. Venus sets only an hour after sunset as March opens, and an hour and a half after the Sun by the 31st. If there are no trees or houses to obscure the view, you may be able to spot brilliant Venus shining low above the western horizon.

Mars was closest to Earth and at its brightest back in late January, and it still outshines Saturn and nearly all the other stars in the March night sky. Mars resembles a bright, copper-colored star high in the northeast during the evening, and stays in view until the wee hours of the morning. As March begins, Mars lies about 72 million miles from Earth, which is about 10 million miles further away than it was at opposition. By month's end, the Earth-Mars distance will have grown to just over 93 million miles, or the same distance as the Sun is from Earth. Correspondingly, as March opens, Mars’s brightness has faded to one-half of what it was at opposition, and by month's end it will have dimmed to nearly one-fourth the opposition value and have the same brightness as nearby star Capella.

Saturn resembles a bright yellow star as it rises above the eastern horizon in late evening. At the beginning of March, Saturn rises by 7:30 pm, and on the 21st it reaches opposition with the Sun, rising as the Sun sets and setting as the Sun rises. Saturn is also closest to Earth this month, though still fainter than Mars. Continuing its residence in the constellation Virgo, Saturn, with its magnificent ring system, is always a wonderful sight in the telescope. Jupiter, which was in conjunction with the Sun on the last day of February, is still too close to the Sun to be observable.

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

No Place to Hide: Missing Primitive Stars Outside Milky Way Uncovered

GARCHING, GERMANY (Feb. 18, 2010) – After years of successful concealment, the most primitive stars outside our Milky Way galaxy have finally been unmasked. New observations using ESO’s Very Large Telescope have been used to solve an important astrophysical puzzle concerning the oldest stars in our galactic neighbourhood — which is crucial for our understanding of the earliest stars in the Universe.

“We have, in effect, found a flaw in the forensic methods used until now,” says Else Starkenburg, lead author of the paper reporting the study. “Our improved approach allows us to uncover the primitive stars hidden among all the other, more common stars.”

Primitive stars are thought to have formed from material forged shortly after the Big Bang, 13.7 billion years ago. They typically have less than one thousandth the amount of chemical elements heavier than hydrogen and helium found in the Sun and are called “extremely metal-poor stars” [1]. They belong to one of the first generations of stars in the nearby Universe. Such stars are extremely rare and mainly observed in the Milky Way.

Cosmologists think that larger galaxies like the Milky Way formed from the merger of smaller galaxies. Our Milky Way’s population of extremely metal-poor or “primitive” stars should already have been present in the dwarf galaxies from which it formed, and similar populations should be present in other dwarf galaxies. “So far, evidence for them has been scarce,” says co-author Giuseppina Battaglia. “Large surveys conducted in the last few years kept showing that the most ancient populations of stars in the Milky Way and dwarf galaxies did not match, which was not at all expected from cosmological models.”

Element abundances are measured from spectra, which provide the chemical fingerprints of stars [2]. The Dwarf galaxies Abundances and Radial-velocities Team [3] used the FLAMES instrument on ESO’s Very Large Telescope to measure the spectra of over 2000 individual giant stars in four of our galactic neighbours, the Fornax, Sculptor, Sextans and Carina dwarf galaxies. Since the dwarf galaxies are typically 300 000 light years away — which is about three times the size of our Milky Way — only strong features in the spectrum could be measured, like a vague, smeared fingerprint. The team found that none of their large collection of spectral fingerprints actually seemed to belong to the class of stars they were after, the rare, extremely metal-poor stars found in the Milky Way.

The team of astronomers around Starkenburg has now shed new light on the problem through careful comparison of spectra to computer-based models. They found that only subtle differences distinguish the chemical fingerprint of a normal metal-poor star from that of an extremely metal-poor star, explaining why previous methods did not succeed in making the identification.

The astronomers also confirmed the almost pristine status of several extremely metal-poor stars thanks to much more detailed spectra obtained with the UVES instrument on ESO’s Very Large Telescope. “Compared to the vague fingerprints we had before, this would be as if we looked at the fingerprint through a microscope,” explains team member Vanessa Hill. “Unfortunately, just a small number of stars can be observed this way because it is very time consuming.”

“Among the new extremely metal-poor stars discovered in these dwarf galaxies, three have a relative amount of heavy chemical elements between only 1/3000 and 1/10 000 of what is observed in our Sun, including the current record holder of the most primitive star found outside the Milky Way,” says team member Martin Tafelmeyer.

“Not only has our work revealed some of the very interesting, first stars in these galaxies, but it also provides a new, powerful technique to uncover more such stars,” concludes Starkenburg. “From now on there is no place left to hide!”

Notes

[1] According to the definition used in astronomy, “metals” are all the elements other than hydrogen and helium. Such metals, except for a very few minor light chemical elements, have all been created by the various generations of stars.

[2] As every rainbow demonstrates, white light can be split up into different colours. Astronomers artificially split up the light they receive from distant objects into its different colours (or wavelengths). However, where we distinguish seven rainbow colours, astronomers map hundreds of finely nuanced colours, producing a spectrum — a record of the different amounts of light the object emits in each narrow colour band. The details of the spectrum — more light emitted at some colours, less light at others — provide tell-tale signs about the chemical composition of the matter producing the light.

[3] The Dwarf galaxies Abundances and Radial-velocities Team (DART) has members from institutes in nine different countries.

More information

This research was presented in a paper to appear in Astronomy and Astrophysics (“The NIR Ca II triplet at low metallicity”, E. Starkenburg et al.). Another paper is also in preparation (Tafelmeyer et al.) that presents the UVES measurements of several primitive stars.

The team is composed of Else Starkenburg, Eline Tolstoy, Amina Helmi, and Thomas de Boer (Kapteyn Astronomical Institute, University of Groningen, the Netherlands), Vanessa Hill (Laboratoire Cassiopée, Université de Nice Sophia Antipolis, Observatoire de la Côte d’Azur, CNRS, France), Jonay I. González Hernández (Observatoire de Paris, CNRS, Meudon, France and Universidad Complutense de Madrid, Spain), Mike Irwin (University of Cambridge, UK), Giuseppina Battaglia (ESO), Pascale Jablonka and Martin Tafelmeyer (Université de Genève, Ecole Polytechnique Fédérale de Lausanne, Switzerland), Matthew Shetrone (University of Texas, McDonald Observatory, USA), and Kim Venn (University of Victoria, Canada).

Links

Science paper

Contacts

Else Starkenburg
Kapteyn Astronomical Institute, University of Groningen
The Netherlands
Tel: +31 50 363 8447
Email: else@astro.rug.nl

Giuseppina Battaglia
ESO
Tel: +49 89 3200 6362
Email: gbattagl@eso.org

Lars Lindberg Christensen
Head of the ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 320 06 761
Cell: +49 173 38 72 621
Email: lars@eso.org

Conversations at KCTS 9: Neil Degrasse Tyson

Enrique Cerna talks with Tyson about his career in science, how he inadvertently started the whole hullabaloo about Pluto, and, in Tyson's words, why "Pluto had it coming."
Airdate: July 3 ,2009.

A New 3-D Map of the Interstellar Gas Within 300 Parsecs from the Sun

PARIS (Feb. 10, 2010) – Astronomy & Astrophysics is publishing new 3D maps of the interstellar gas in the local area around our Sun. A French-American team of astronomers presents new absorption measurements towards more than 1800 stars. They were able to characterize the properties of the interstellar gas within each sight line.

FIGURE CAPTION - Map of partially ionized interstellar gas within 300 parsecs around the Sun, as viewed in the Galactic plane. Triangles represent the sight-line positions of the stars used to produce the map. White to dark shading represents the low to high values of the gas density, and orange shading is for areas with no reliable measurement. The Local Cavity is shown as the white area of low density gas that surrounds the Sun at about 80 parsecs.

This week, Astronomy & Astrophysics publishes new 3D maps of the interstellar gas situated in an area 300 parsecs around the Sun. A French-American team of astronomers presents new measurements of the absorption by the interstellar gas in the Sun's local area. Knowledge of the interstellar medium properties, including the spatial distribution, dynamics, and the chemical and physical characteristics, allow astronomers to better understand the interplay between the evolution of stars and their exchange of matter with the ambient interstellar medium. The local area around our Sun has been studied with many surveys at various wavelengths, but the whole picture is still far from being either complete or fully understood.

The team, led by Barry Y. Welsh and his colleagues R. Lallement and J.-L. Vergely, presents new, high spectral resolution measurements of the calcium (CaII) K line (at 3933 Å) and the sodium doublet (at 5889 and 5895 Å). These absorption lines have long been used to study the interstellar medium. The CaII K lines were first observed in 1904 by German astronomer J. Hartmann, in the spectrum of the star δ Orionis. This first detection of interstellar gas set the stage for the early studies of interstellar medium. The sodium (NaI) doublet was later discovered in 1919 toward δ Orionis and β Scorpii. The CaII K line and the NaI doublet are complementary: the first one is sensitive to partially ionized gas, and the second one traces cold and neutral interstellar gas.

The team combined their new data (mostly recorded at the European Southern Observatory in Chile) with previously published results. The new paper represents a catalog of absorption measurements towards 1857 stars located 800 parsecs from the Sun. Figure 1 shows the NaI map of the interstellar gas density within 300 parsecs. The white area surrounding the Sun (i.e., at the center of the map) corresponds to a very low-density area of neutral gas, known as the Local Cavity. It is about 80 parsecs in radius in most directions and is surrounded by a highly fragmented “wall” of dense neutral gas. The various gaps in the wall are termed “interstellar tunnels” and represent rarefied pathways into other surrounding interstellar cavities. Maps of the distribution of CaII have never been made before, and they reveal that the Local Cavity contains numerous filamentary structures of partially ionized gas that appear to form in a honeycomb-like pattern of small interstellar cells.

Theories of the general interstellar medium require that large rarefied cavities exist, having been formed by the combined action of energetic supernova events and the outflowing winds of clusters of hot and young stars. The history of our Local Cavity, within which the Sun resides, is still speculative, but many believe that it was created about 15 million years ago by a series of supernova outbursts, with the last re-heating happening about 3 million years ago.

The team includes B. Y. Welsh (UCL Berkeley, USA), R. Lallement, S. Raimond (Université Versailles-St Quentin/CNRS, France), and J.-L. Vergely (ACRI-ST, France).

A Little Telescope Goes a Long Way

PASADENA, CA (Feb. 9, 2010) – NASA astronomers have successfully demonstrated that a David of a telescope can tackle Goliath-size questions in the quest to study Earth-like planets around other stars. Their work, reported today in the journal Nature, provides a new tool for ground-based observatories, promising to accelerate by years the search for prebiotic, or life-related, molecules on planets orbiting stars beyond our solar system.

FIGURE CAPTION – This artist concept shows the planetary system called HD 189733, located 63 light-years away in the constellation Vulpecula. Image credit: NASA/JPL-Caltech

The scientists reported on a new technique used with a relatively small Earth-based telescope to identify an organic molecule in the atmosphere of a Jupiter-size planet nearly 63 light-years away. The measurement revealed details of the exoplanet's atmospheric composition and conditions, an unprecedented achievement from an Earth-based observatory.

The surprising new finding comes from a venerable 30-year-old, 3-meter-diameter (10-foot) telescope that ranks 40th among ground-based telescopes - NASA's Infrared Telescope Facility atop Mauna Kea, Hawaii.

The new technique promises to further speed the work of studying planet atmospheres by enabling studies from the ground that were previously possible only through a few very high-performance space telescopes. "Given favorable observing conditions, this work suggests we may be able to detect organic molecules in the atmospheres of terrestrial planets with existing instruments," said lead author Mark Swain, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. This can allow fast and economical advances in focused studies of exoplanet atmospheres, accelerating our understanding of the growing stable of exoplanets.

"The fact that we have used a relatively small, ground-based telescope is exciting because it implies that the largest telescopes on the ground, using this technique, may be able to characterize terrestrial exoplanet targets," Swain said.

Currently, more than 400 exoplanets are known. Most are gaseous like Jupiter, but some "super-Earths" are thought to be large terrestrial, or rocky, worlds. A true Earth-like planet, with the same size as our planet and distance from its star, has yet to be discovered. NASA's Kepler mission is searching from space now, and is expected to find several of these earthly worlds by the end of its three-and-a-half-year prime mission.

On Aug. 11, 2007, Swain and his team turned the infrared telescope to the hot, Jupiter-size planet HD 189733b in the constellation Vulpecula. Every 2.2 days, the planet orbits a K-type main sequence star slightly cooler and smaller than our sun. HD189733b had already yielded breakthrough advances in exoplanet science, including detections of water vapor, methane and carbon dioxide, using space telescopes. Using the new technique, the astronomers successfully detected carbon dioxide and methane in the atmosphere of HD 189733b with a spectrograph, which splits light into its components to reveal the distinctive spectral signatures of different chemicals. Their key work was development of a novel calibration method to remove systematic observation errors caused by the variability of Earth's atmosphere and instability due to the movement of the telescope system as it tracks its target.

"As a consequence of this work, we now have the exciting prospect that other suitably equipped yet relatively small ground-based telescopes should be capable of characterizing exoplanets," said John Rayner, the NASA Infrared Telescope Facility support scientist who built the SpeX spectrograph used for these measurements. "On some days we can't even see the sun with the telescope, and the fact that on other days we can now obtain a spectrum of an exoplanet 63 light-years away is astonishing."

In the course of their observations, the team found unexpected bright infrared emission from methane that stands out on the day side of HD189733b, indicating some kind of activity in the planet's atmosphere. Swain said this puzzling feature could be related to the effect of ultraviolet radiation from the planet's parent star hitting the planet's upper atmosphere, but more detailed study is needed. "This feature indicates the surprises that await us as we study exoplanet atmospheres," he added.

"An immediate goal for using this technique is to more fully characterize the atmosphere of this and other exoplanets, including detection of organic and possibly prebiotic molecules" like those that preceded the evolution of life on Earth, said Swain. "We're ready to undertake that task." Some early targets will be the super-Earths. Used in synergy with observations from NASA's Hubble, Spitzer and the future James Webb Space Telescope, the new technique "will give us an absolutely brilliant way to characterize super-Earths," Swain said.

Other authors are Pieter Deroo, Gautam Vasisht and Pin Chen of JPL; Caitlin A. Griffith of the University of Arizona, Tucson; Giovanna Tinetti of University College London; Ian J. Crossfield of UCLA; Azam Thatte of the Georgia Institute of Technology, Atlanta; Jeroen Bouwman, Cristina Afonso and Thomas Henning of Max-Planck Institute for Astronomy, Heidelberg, Germany; and Daniel Angerhausen of the German SOFIA Institute, Stuttgart, Germany.

The work was carried out with funding from NASA's Office of Space Science in Washington, D.C. The NASA Infrared Telescope Facility is managed by the University of Hawaii's Institute for Astronomy. JPL is managed by the California Institute of Technology for NASA.

Whitney Clavin 818-354-4673

Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

"Ingredients for Life" Present on Saturn's Moon Enceladus

LONDON (Feb. 8, 2010) – Some of ‘the major ingredients for life’ are present on one of Saturn’s moons, according to UCL scientists.

A team from the Mullard Space Science Laboratory working on the Cassini-Huygens mission have found negatively charged water ions in the ice plume of Enceladus.

Figure Caption – Cassini captured this stunning mosaic of Enceladus as the spacecraft sped away from the geologically active moon of Saturn.

Their analysis of data gathered during the spacecraft’s plume fly-throughs in 2008 provide evidence for the presence of liquid water.

The spacecraft’s plasma spectrometer, used to gather this data, also found other species of negatively charged ions including hydrocarbons.

MSSL’s Professor Andrew Coates, lead author of a paper on the latest discovery, said: “While it’s no surprise that there is water there, these short-lived ions are extra evidence for sub-surface water and where there’s water, carbon and energy, some of the major ingredients for life are present.

The surprise for us was to look at the mass of these ions. There were several peaks in the spectrum, and when we analysed them we saw the effect of water molecules clustering together one after the other.”

Enceladus thus joins Earth, Titan and comets where negatively charged ions are known to exist in the solar system. Negative oxygen ions were discovered in Earth’s ionosphere at the dawn of the space age. At Earth’s surface, negative water ions are present where liquid water is in motion, such as waterfalls or crashing ocean waves.

The plasma spectrometer measures the density, flow velocity and temperature of ions and electrons that enter the instrument. But since the discovery of Enceladus’ water ice plume, the instrument has also successfully captured and analysed samples of material in the jets.

Early in its mission, Cassini-Huygens discovered the plume that fountains water vapour and ice particles above Enceladus. Since then, scientists have found that these water products dominate Saturn’s magnetic environment and create Saturn’s huge E-ring.

At Titan, the same instrument detected extremely large negative hydrocarbon ions with masses up to 13,800 times that of hydrogen. Dr Coates and his colleagues believe large ions are the source of the smog-like haze that blocks most of Titan’s surface from view.

The new findings add to astronomers’ growing knowledge of the detailed chemistry of Enceladus’ plume and Titan’s atmosphere, giving new understanding of
environments beyond Earth where prebiotic or life-sustaining environments might exist.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), which funds the UK involvement in Cassini-Huygens, said: “This measurement of water ions in the ice plume of Enceladus is incredibly exciting and provides us with further hope of finding water and maybe even life on this distant icy moon.”

The Cassini-Huygens mission is a co-operative project of NASA, the European Space Agency and the Italian Space Agency.

Astronomers Find Rare Beast by New Means

SOCORRO, NEW MEXICO (Feb. 3, 2010) – For the first time, astronomers have found a supernova explosion with properties similiar to a gamma-ray burst, but without seeing any gamma rays from it. The discovery, using the National Science Foundation's Very Large Array (VLA) radio telescope, promises, the scientists say, to point the way toward locating many more examples of these mysterious explosions.

FIGURE CAPTION – Artist's conception of an "Engine-driven" supernova explosion with accretion disk and high-velocity jets. (Credit: Bill Saxton, NRAO/AUI/NSF)

"We think that radio observations will soon be a more powerful tool for finding this kind of supernova in the nearby Universe than gamma-ray satellites," said Alicia Soderberg, of the Harvard-Smithsonian Center for Astrophysics.

The telltale clue came when the radio observations showed material expelled from the supernova explosion, dubbed SN2009bb, at speeds approaching that of light. This characterized the supernova, first seen last March, as the type thought to produce one kind of gamma-ray burst.

"It is remarkable that very low-energy radiation, radio waves, can signal a very high-energy event," said Roger Chevalier of the University of Virginia.

When the nuclear fusion reactions at the cores of very massive stars no longer can provide the energy needed to hold the core up against the weight of the rest of the star, the core collapses catastrophically into a superdense neutron star or black hole. The rest of the star's material is blasted into space in a supernova explosion. For the past decade or so, astronomers have identified one particular type of such a "core-collapse supernova" as the cause of one kind of gamma-ray burst.

Not all supernovae of this type, however, produce gamma-ray bursts. "Only about one out of a hundred do this," according to Soderberg.

In the more-common type of such a supernova, the explosion blasts the star's material outward in a roughly-spherical pattern at speeds that, while fast, are only about 3 percent of the speed of light. In the supernovae that produce gamma-ray bursts, some, but not all, of the ejected material is accelerated to nearly the speed of light.

The superfast speeds in these rare blasts, astronomers say, are caused by an "engine" in the center of the supernova explosion that resembles a scaled-down version of a quasar. Material falling toward the core enters a swirling disk surrounding the new neutron star or black hole. This accretion disk produces jets of material boosted at tremendous speeds from the poles of the disk.

"This is the only way we know that a supernova explosion could accelerate material to such speeds," Soderberg said.

Until now, no such "engine-driven" supernova had been found any way other than by detecting gamma rays emitted by it.

"Discovering such a supernova by observing its radio emission, rather than through gamma rays, is a breakthrough. With the new capabilities of the Expanded VLA coming soon, we believe we'll find more in the future through radio observations than with gamma-ray satellites," Soderberg said.

Why didn't anyone see gamma rays from this explosion? "We know that the gamma-ray emission is beamed in such blasts, and this one may have been pointed away from Earth and thus not seen," Soderberg said. In that case, finding such blasts through radio observations will allow scientists to discover a much larger percentage of them in the future.

"Another possibility," Soderberg adds, "is that the gamma rays were 'smothered' as they tried to escape the star. This is perhaps the more exciting possibility since it implies that we can find and identify engine-driven supernovae that lack detectable gamma rays and thus go unseen by gamma-ray satellites."

One important question the scientists hope to answer is just what causes the difference between the "ordinary" and the "engine-driven" core-collapse supernovae. "There must be some rare physical property that separates the stars that produce the 'engine-driven' blasts from their more-normal cousins," Soderberg said. "We'd like to find out what that property is."

One popular idea is that such stars have an unusually low concentration of elements heavier than hydrogen. However, Soderberg points out, that does not seem to be the case for this supernova.

Soderberg and Chevalier worked with Alak Ray and Sayan Chakrabarti of the Tata Institute of Fundamental Research in India; Poonam Chandra of the Royal Military College of Canada; and a large group of collaborators at the Harvard-Smithsonian Center for Astrophysics. The scientists reported their findings in the January 28 issue of the journal Nature.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

The Night Sky: February 2010

The Night Sky in February 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 13thFull "Snow Moon" on the 28th

Stars and Constellations

February skies present a brilliant tapestry of stars that contrasts with the frigid temperatures of winter nights. The constellation Cassiopeia, which represents the throne of the Queen of ancient Ethiopia, can be seen high in the northwest, looking like the letter "M." Even higher in the northwest above Cassiopeia is Perseus, whose brightest stars form a “horn” shape which opens toward the nearby Pleiades cluster. Nearly overhead on February evenings is Auriga, the Charioteer, with the bright yellow star Capella as its "eye." Just south of Auriga is Taurus the Bull, with its bright orange star Aldebaran. Aldebaran is classed as a red giant star, and it stands in the foreground of a more distant loose cluster of stars known as the Hyades. Further to the west of the Hyades is the more famous and compact Pleiades star cluster, looking like a miniature dipper.

Following Taurus to the east is Gemini, the Twins, and its two brightest stars Pollux and Castor. Their proximity to each other is merely perspective: in reality they are about 10 light years apart. Pollux has a slight yellow or orange tinge to it, while Castor is more white in color. Remarkably, the Castor system consists of a total of six gravitationally bound stars, five of which can be seen individually in a telescope. In ancient mythology, Pollux and Castor were the offspring of the god Zeus and the mortal Queen of Sparta. Pollux was born immortal, but Castor was mortal. Both brothers were among the crew of Jason and the Argonauts. Gemini is a significant zodiac constellation because it contains the summer solstice point, which the Sun passes through on or about June 21, the first day of summer. In fact, the Sun’s apparent path around the celestial sphere (defined as the ecliptic) takes it within the boundaries of Gemini during the time interval from June 20 through July 20.

Orion the Hunter now stands high in the south, dominating the midwinter night sky. Orion's two brightest stars, Betelgeuse and Rigel, are classed, respectively, as red and blue supergiants, and are among the most luminous stars known. Orion's "sword" contains the Great Orion Nebula, a vast complex of star formation nearly 1500 light years from our solar system. Just below and to the left of Orion is the brightest star in the night sky, Sirius, in the constellation Canis Major. Sirius is one of the Sun’s nearest neighbors, at only 8.5 light years distance. Sirius is actually a binary star system, consisting of a bright primary star with a very faint companion. The companion is now known to be a white dwarf, or degenerate star, in which nuclear reactions are no longer sustained, and possessing a diameter of only 1/100 that of the Sun, or nearly the same size as planet Earth. Just a bit further to the east of Sirius is its neighbor Procyon in Canis Minor. Like Sirius, Procyon is also nearby, at 11 light years away, and also like Sirius, Procyon is a binary star system containing a white dwarf. Betelgeuse, Sirius, and Procyon comprise a "winter triangle." Though not nearly as famous as its summer counterpart, the winter triangle is nevertheless easy to pick out since the stars are bright.

After about 8 pm, you can spot some of the stars of spring mounting the sky in the east. In particular, Regulus in the constellation Leo, lies low in the east-northeast. Looking a little further northward, you may spot the Big Dipper, which is part of the constellation Ursa Major, or Big Bear, rising in the north-northeast. Seasoned skywatchers know that when they see these celestial signs spring is is just around the corner!

Naked-Eye Planets In the Evening and Morning Sky

Venus was in conjunction with the Sun last month, and is still too close to the Sun to be visible at the beginning of February. Toward the middle of the month, however, Venus begins to emerge from the evening twilight. At midmonth, Venus passes very close to Jupiter, which is sinking toward the Sun. By month’s end, Venus sets nearly an hour after sunset and, for those with an unobstructed horizon, can be seen shining low above the western horizon.

The Giant Planet, Jupiter, can still be spotted very low in the southwestern sky after sunset in early February, but not for long ; it will vanish into the evening twilight before the end of the month. Jupiter, which resembles a brilliant cream-colored star hovering above the southwestern horizon after darkness falls, has dominated the evening sky since last summer, but this month it yields the celestial stage to Mars . At the beginning of February, Jupiter sets at 7 pm, or only about an hour and a half after sunset. On the 16^th, descending Jupiter passes only a Full Moon’s width fromVenus, which is moving the opposite way. On the last day of February, Jupiter will be in conjunction with the Sun and unobservable.

As Jupiter sets into the western twilight, the Red Planet, Mars, rises in the eastern sky. Mars, which was closest to Earth and at opposition with the Sun at the end of January, now reigns supreme among planets in the night sky. Mars resembles a bright orange star in the northeast during the early evening hours, but it gets higher as the night progresses, and stays in good view until shortly before sunrise. Even a small telescope should reveal some of the surface markings and polar caps. At the beginning of the month, Mars is about as bright as Sirius, the brightest star in the night sky, which can be located just below and to the left of Orion. As Earth pulls away from Mars over the next few weeks, Mars will begin to dim in brightness, and by month’s end, Mars will have faded to about half the brightness it had when at opposition.

Saturn, now in eastern Virgo, rises by 9:30 pm at the beginning of February, and looks like a bright yellow star rising above the eastern horizon in late evening. Saturn’s yellow color contrasts with the blue-white sparkle ofVirgo’s brightest star, Spica which lies to Saturn’s lower left. By month’s end, Saturn sets around 7:30 pm, and next month will be in opposition with the Sun. Saturn is not as bright as Mars, but its fabulous ring system is worth a look through a telescope.

Mercury, which reached greatest morning elongation with the Sun on January 27^th, is still in good position for morning viewing as February opens. To spot Mercury, look for what appears to be a bright yellow star low in the south east a half-hour to an hour before sunrise. As February progresses, however, Mercury will sink into the morning twilight and be unobservable by month's end.

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

Black Hole Hunters Set New Distance Record

GARCHING, GERMANY (Jan. 28, 2010) – Astronomers using ESO’s Very Large Telescope have detected, in another galaxy, a stellar-mass black hole much farther away than any other previously known. With a mass above fifteen times that of the Sun, this is also the second most massive stellar-mass black hole ever found. It is entwined with a star that will soon become a black hole itself.

The stellar-mass black holes [1] found in the Milky Way weigh up to ten times the mass of the Sun and are certainly not be taken lightly, but, outside our own galaxy, they may just be minor-league players, since astronomers have found another black hole with a mass over fifteen times the mass of the Sun. This is one of only three such objects found so far.

The newly announced black hole lies in a spiral galaxy called NGC 300, six million light-years from Earth. “This is the most distant stellar-mass black hole ever weighed, and it’s the first one we’ve seen outside our own galactic neighbourhood, the Local Group,” says Paul Crowther, Professor of Astrophysics at the University of Sheffield and lead author of the paper reporting the study. The black hole’s curious partner is a Wolf–Rayet star, which also has a mass of about twenty times as much as the Sun. Wolf–Rayet stars are near the end of their lives and expel most of their outer layers into their surroundings before exploding as supernovae, with their cores imploding to form black holes.

In 2007, an X-ray instrument aboard NASA’s Swift observatory scrutinised the surroundings of the brightest X-ray source in NGC 300 discovered earlier with the European Space Agency’s XMM-Newton X-ray observatory. “We recorded periodic, extremely intense X-ray emission, a clue that a black hole might be lurking in the area,” explains team member Stefania Carpano from ESA.

Thanks to new observations performed with the FORS2 instrument mounted on ESO’s Very Large Telescope, astronomers have confirmed their earlier hunch. The new data show that the black hole and the Wolf–Rayet star dance around each other in a diabolic waltz, with a period of about 32 hours. The astronomers also found that the black hole is stripping matter away from the star as they orbit each other.

“This is indeed a very ‘intimate’ couple,” notes collaborator Robin Barnard. “How such a tightly bound system has been formed is still a mystery.”

Only one other system of this type has previously been seen, but other systems comprising a black hole and a companion star are not unknown to astronomers. Based on these systems, the astronomers see a connection between black hole mass and galactic chemistry. “We have noticed that the most massive black holes tend to be found in smaller galaxies that contain less ‘heavy’ chemical elements,” says Crowther [2]. “Bigger galaxies that are richer in heavy elements, such as the Milky Way, only succeed in producing black holes with smaller masses.” Astronomers believe that a higher concentration of heavy chemical elements influences how a massive star evolves, increasing how much matter it sheds, resulting in a smaller black hole when the remnant finally collapses.

In less than a million years, it will be the Wolf–Rayet star’s turn to go supernova and become a black hole. “If the system survives this second explosion, the two black holes will merge, emitting copious amounts of energy in the form of gravitational waves as they combine [3],” concludes Crowther. However, it will take some few billion years until the actual merger, far longer than human timescales. “Our study does however show that such systems might exist, and those that have already evolved into a binary black hole might be detected by probes of gravitational waves, such as LIGO or Virgo [4].”

Notes

[1] Stellar-mass black holes are the extremely dense, final remnants of the collapse of very massive stars. These black holes have masses up to around twenty times the mass of the Sun, as opposed to supermassive black holes, found in the centre of most galaxies, which can weigh a million to a billion times as much as the Sun. So far, around 20 stellar-mass black holes have been found.

[2] In astronomy, heavy chemical elements, or “metals”, are any chemical elements heavier than helium.

[3] Predicted by Einstein’s theory of general relativity, gravitational waves are ripples in the fabric of space and time. Significant gravitational waves are generated whenever there are extreme variations of strong gravitational fields with time, such as during the merger of two black holes. The detection of gravitational waves, never directly observed to date, is one of the major challenges for the next few decades.

[4] The LIGO and Virgo experiments have the goal of detecting gravitational waves using sensitive interferometers in Italy and the United States.

More information

This research was presented in a letter to appear in the Monthly Notices of the Royal Astronomical Society (NGC 300 X-1 is a Wolf–Rayet/Black Hole binary, P.A. Crowther et al.).

The team is composed of Paul Crowther and Vik Dhillon (University of Sheffield, UK), Robin Barnard and Simon Clark (The Open University, UK), and Stefania Carpano and Andy Pollock (ESAC, Madrid, Spain).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory, and VISTA, the largest survey telescope in the world. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Contacts

Paul Crowther
University of Sheffield, UK
Tel: +44-114 222 4291
Email: Paul.Crowther (at) sheffield.ac.uk

Stefania Carpano
ESTEC, ESA
The Netherlands
Tel: +31-71-5654827
Email: scarpano (at) rssd.esa.int

Usage

Newborn Black Holes May Add Power to Many Exploding Stars

WASHINGTON, DC (Jan. 27, 2010) – Astronomers studying two exploding stars, or supernovae, have found evidence the blasts received an extra boost from newborn black holes. The supernovae were found to emit jets of particles traveling at more than half the speed of light.

Previously, the only catastrophic events known to produce such high-speed jets were gamma-ray bursts, the universe's most luminous explosions. Supernovae and the most common type of gamma-ray bursts occur when massive stars run out of nuclear fuel and collapse. A neutron star or black hole forms at the star's core, triggering a massive explosion that destroys the rest of the star.

"The explosion dynamics in typical supernovae limit the speed of the expanding matter to about three percent the speed of light," explained Chryssa Kouveliotou, an astrophysicst at NASA's Marshall Space Flight Center in Huntsville, Ala., co-author of one of the new studies. "Yet, in these new objects, we're tracking gas moving some 20 times faster than this."

The new results, published in this week's edition of the journal Nature, used observations from several space and ground-based observatories, including NASA's SWIFT satellite.

The astronomers discovered the ultrafast debris by studying two supernovae at radio wavelengths using numerous facilities, including the National Science Foundation's Very Large Array in Socorro, N.M., and the Robert C. Byrd Green Bank Telescope in West Virginia. One team used the real-time operating mode of the European Very Long Baseline Interferometry Network, an international collaboration of radio telescopes, to rapidly analyze data.

"In every respect, these objects look like gamma-ray bursts -- except that they produced no gamma rays," said Alicia Soderberg at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Soderberg led a team that studied SN 2009bb, a supernova discovered in March 2009. It exploded in the spiral galaxy NGC 3278, located about 130 million light-years away.

The other object is SN 2007gr, which was first detected in August 2007 in the spiral galaxy NGC 1058, some 35 million light-years away. The study team, which included Kouveliotou and Alexander van der Horst, a NASA Postdoctoral Program Fellow in Huntsville, was led by Zsolt Paragi at the Netherlands-based Joint Institute for Very Long Baseline Interferometry in Europe.

The researchers searched for gamma-ray signals associated with the supernovae using archived records in the Gamma-Ray Burst Coordination Network located at NASA's Goddard Space Flight Center in Greenbelt, Md. The project distributes and archives observations of gamma-ray bursts by NASA's SWIFT spacecraft, the Fermi Gamma-ray Space Telescope and many others. However, no bursts coincided with the supernovae.

Unlike typical core-collapse supernovae, the stars that produce gamma-ray bursts possess what astronomers call a "central engine" -- likely a nascent black hole -- that drives particle jets clocked at more than 99 percent the speed of light.

By contrast, the fastest outflows detected from SN 2009bb reached 85 percent of the speed of light and SN 2007gr reached more than 60 percent of light speed.

"These observations are the first to show some supernovae are powered by a central engine," Soderberg said. "These new radio techniques now give us a way to find explosions that resemble gamma-ray bursts without relying on detections from gamma-ray satellites."

Perhaps as few as one out of every 10,000 supernovae produce gamma rays that we detect as a gamma-ray burst. In some cases, the star's jets may not be angled in a way to produce a detectable burst. In others, the energy of the jets may not be enough to allow them to overcome the overlying bulk of the star.

"We've now found evidence for the unsung crowd of supernovae -- those with relatively dim and mildly relativistic jets that only can be detected nearby," Kouveliotou said. "These likely represent most of the population."

For more information, images and animation about this discovery, visit:

http://www.nasa.gov/swift

Astronomers: The end is nigher than we expected

CANBERRA, AUSTRALIA (Jan. 26, 2010) – Cars run out of petrol, stars run out of fuel and galaxies collapse into black holes. As they do, the universe and everything in it is gradually running down. But how run down is it? Researchers from The Australian National University have found that the universe is 30 times more run down than previously thought.

PhD student Chas Egan and Dr Charley Lineweaver from the ANU Research School of Astronomy and Astrophysics have computed the entropy of the universe. Scientists compute entropy to figure out how efficient an engine is or how much work can be extracted from a fuel or how run down and disordered a system is. Using new data on the number and size of black holes they found that the universe contains 30 times more entropy than earlier estimates.

“We considered all contributions to the entropy of the observable universe: stars, star light, the cosmic microwave background. We even made an estimate of the entropy of dark matter. But it’s the entropy of super-massive black holes that dominates the entropy of the universe. When we used the new data on the number and size of super-massive black holes, we found that the entropy of the observable universe is about 30 times larger than previous calculations,” said Mr Egan.

“Contrary to common opinion, the maintenance of all the complicated structures we see around us – galaxies, stars, hurricanes and kangaroos – have the net effect of increasing the disorder and entropy of the universe. But to be fair, their contributions are negligible compared to the entropy of super-massive black holes,” added Dr Lineweaver.

The researchers’ results have important implications for terrestrial and extraterrestrial life. “The universe started out in a low entropy state and, in accordance with the second law of thermodynamics, the entropy has been increasing ever since,” Mr Egan said. “This is important because the amount of energy available to life in the universe, including terrestrial life, depends on the entropy of the universe. We’d like to know how much energy will be available to life forms anywhere in the universe, and where this energy is. The first step in this procedure is to determine the entropy of the universe. That is what we did.”

Dr Lineweaver said that the next step in the research is to figure out how close we are to maximum entropy, how much entropy is being produced and how much time we have left before the universe and all life in it dies in the inevitable heat death.

Their research paper A Larger Estimate of the Entropy of the Universe has just been accepted for publication in the Astrophysical Journal. A copy of the paper is available at http://arxiv.org/abs/0909.3983v2 and at www.mso.anu.edu.au/~charley/publications.html

Filed under:

Media Release, ANU College of Physical Sciences, Science

Contacts:

For more information or to arrange interviews: Chas Egan 0405 375 210; Dr Charley Lineweaver 02 6125 0822 ANU media office: Simon Couper 02 6125 4171, 0416 249 241

Dense Gas in Ultraluminous Infrared Galaxies

CAMBRIDGE, MA (Jan. 18, 2010) – Ultraluminous infrared galaxies have luminosities that exceed a trillion suns. (For comparison, the Milky Way's luminosity is only that of about ten billion suns.) Extreme infrared activity is known to be associated with interacting galaxies, and optical imaging indeed shows that many ultraluminous systems are in collision. The physical mechanism(s) that actually power the luminosity, however, are still not understood. Might the same process(es) be underway at a low level in our galaxy?

One of the primary sources of global energy production in galaxies is star formation, and ultraluminous galaxies show all the diagnostic signs of having vigorous star formation. In a new paper by CfA astronomer Desika Narayanan and six colleagues, the case is made that this activity is the result of a higher proportion of dense clouds of gas in these objects, and that these clumps are probably the result of the collision. The conclusion counters earlier arguments that X-rays from the nuclear black holes are responsible by chemically enhancing the gas with molecules that facilitate star formation.

The astronomers reached their conclusions by analyzing a set of thirty-four nearby, infrared luminous galaxies in the emitted light of three key molecules: CO, ionized HCO, and HCN. These species are sensitive probes of total gas densities ranging from about one thousand molecules per cubic centimeter to nearly one hundred million per cubic centimeter. The team compared the brightness of the molecular emission from each species to the overall galaxy luminosity, and found a strong correlation in the sense that the brighter the lines, the higher the luminosity. This result had been well known before, and seemed sensible since new stars form out of the gas. New in the study is the authors' finding that denser gas makes stars at a faster rate: the three species in this study, for example, sample gas that spans a factor of about one million in stellar production rates. The new research convincingly shows that other suggested mechanisms, for example enhanced chemical abundances, are less important. In addition, the paper provides a welcome, relatively comprehensive study of gas densities in luminous galaxies.

Carl Sagan Discusses the 4th Dimenion

Carl Sagan talks about the 4th dimension and how it is possible to understand curved space time as used by Einstein in his general theory of relativity.

In All the Universe, Just 10 Percent of Solar Systems Are Like Ours

WASHINGTON, DC (Jan. 5, 2010) – In their quest to find solar systems analogous to ours, astronomers have determined how common our solar system is.

They’ve concluded that about 15 percent of stars in the galaxy host systems of planets like our own, with several gas giant planets in the outer part of the solar system.

FIGURE CAPTION – The planets are shown in the correct order of distance from the Sun, the correct relative sizes, and the correct relative orbital distances. The sizes of the bodies are greatly exaggerated relative to the orbital distances. The faint rings of Jupiter, Uranus, and Neptune are not shown. Eris, Haumea, and Makemake do not appear in the illustration owing to their highly tilted orbits. The dwarf planet Ceres is not shown separately; it resides in the asteroid belt between Mars and Jupiter. (Credit: NASA)

“Now we know our place in the universe,” said Ohio State University astronomer Scott Gaudi. “Solar systems like our own are not rare, but we’re not in the majority, either.”

Gaudi reported the results of the new study on Tuesday, January 5 at the American Astronomical Society Meeting in Washington, DC, when he accepts the Helen B. Warner Prize for Astronomy.

The find comes from a worldwide collaboration headquartered at Ohio State called the Microlensing Follow-Up Network (MicroFUN), which searches the sky for extrasolar planets.

MicroFUN astronomers use a method called gravitational microlensing, which occurs when one star happens to cross in front of another as seen from Earth. The nearer star magnifies the light from the more distant star like a lens. If planets are orbiting the lens star, they boost the magnification briefly as they pass by.

This method is especially good at detecting giant planets in the outer reaches of solar systems -- planets analogous to our own Jupiter.

This latest MicroFUN result is the culmination of 10 years’ work -- and one sudden epiphany, explained Gaudi and Andrew Gould, professor of astronomy at Ohio State.

Ten years ago, Gaudi wrote his doctoral thesis on a method for calculating the likelihood that extrasolar planets exist. At the time, he concluded that less than 45 percent of stars could harbor a configuration similar to our own solar system.

Then, in December of 2009, Gould was examining a newly discovered planet with Cheongho Han of the Institute for Astrophysics at Chungbuk National University in Korea. The two were reviewing the range of properties among extrasolar planets discovered so far, when Gould saw a pattern.

“Basically, I realized that the answer was in Scott’s thesis from 10 years ago,” Gould said. “Using the last four years of MicroFUN data, we could add a few robust assumptions to his calculations, and we could now say how common planet systems are in our galaxy.”

The find boils down to a statistical analysis: in the last four years, the MicroFUN survey has discovered only one solar system like our own -- a system with two gas giants resembling Jupiter and Saturn, which astronomers discovered in 2006 and reported in the journal Science in 2008.

“We’ve only found this one system, and we should have found about six by now -- if every star had a solar system like Earth’s,” Gaudi said.

The slow rate of discovery makes sense if only a small number of systems -- around 15 percent -- are like ours, they determined.

“While it is true that this initial determination is based on just one solar system and our final number could change a lot, this study shows that we can begin to make this measurement with the experiments we are doing today,” Gaudi added.

As to the possibility of life as we know it existing elsewhere in the galaxy, scientists will now be able to make a rough guess based on how many solar systems are like our own.

Our solar system may be a minority, but Gould said that the outcome of the study is actually positive.

“With billions of stars out there, even narrowing the odds to 15 percent leaves a few hundred million systems that might be like ours,” he said.

This research was partly funded by the National Science Foundation.

Contact: Scott Gaudi, (614) 292-1914; Gaudi.1@osu.edu
Andrew Gould, (614) 292-1892; Gould.34@osu.edu
Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

NASA's Kepler Space Telescope Discovers Five Exoplanets

PASADENA, CA (Jan. 4, 2010) – NASA's Kepler space telescope, designed to find Earth-size planets in the habitable zone of sun-like stars, has discovered its first five new exoplanets, or planets beyond our solar system.

Kepler's high sensitivity to both small and large planets enabled the discovery of the exoplanets, named Kepler 4b, 5b, 6b, 7b and 8b. The discoveries were announced Monday, Jan. 4, by members of the Kepler science team during a news briefing at the American Astronomical Society meeting in Washington.

"These observations contribute to our understanding of how planetary systems form and evolve from the gas and dust disks that give rise to both the stars and their planets," said William Borucki of NASA's Ames Research Center in Moffett Field, Calif. Borucki is the mission's science principal investigator. "The discoveries also show that our science instrument is working well. Indications are that Kepler will meet all its science goals."

Known as "hot Jupiters" because of their high masses and extreme temperatures, the new exoplanets range in size from similar to Neptune to larger than Jupiter. They have orbits ranging from 3.3 to 4.9 days. Estimated temperatures of the planets range from 2,200 to 3,000 degrees Fahrenheit, hotter than molten lava and much too hot for life as we know it. All five of the exoplanets orbit stars hotter and larger than Earth's sun.

"It's gratifying to see the first Kepler discoveries rolling off the assembly line," said Jon Morse, director of the Astrophysics Division at NASA Headquarters in Washington. "We expected Jupiter-size planets in short orbits to be the first planets Kepler could detect. It's only a matter of time before more Kepler observations lead to smaller planets with longer-period orbits, coming closer and closer to the discovery of the first Earth analog."

Launched on March 6, 2009, from Cape Canaveral Air Force Station in Florida, the Kepler mission continuously and simultaneously observes more than 150,000 stars. Kepler's science instrument, or photometer, already has measured hundreds of possible planet signatures that are being analyzed.

While many of these signatures are likely to be something other than a planet, such as small stars orbiting larger stars, ground-based observatories have confirmed the existence of the five exoplanets. The discoveries are based on approximately six weeks' worth of data collected since science operations began on May 12, 2009.

Kepler looks for the signatures of planets by measuring dips in the brightness of stars. When planets cross in front of, or transit, their stars as seen from Earth, they periodically block the starlight. The size of the planet can be derived from the size of the dip. The temperature can be estimated from the characteristics of the star it orbits and the planet's orbital period.

Kepler will continue science operations until at least November 2012. It will search for planets as small as Earth, including those that orbit stars in a warm, habitable zone where liquid water could exist on the surface of the planet. Since transits of planets in the habitable zone of solar-like stars occur about once a year and require three transits for verification, it is expected to take at least three years to locate and verify an Earth-size planet.

According to Borucki, Kepler's continuous and long-duration search should greatly improve scientists' ability to determine the distributions of planet size and orbital period in the future. "Today's discoveries are a significant contribution to that goal," Borucki said. "The Kepler observations will tell us whether there are many stars with planets that could harbor life, or whether we might be alone in our galaxy."

Kepler is NASA's 10th Discovery mission. NASA Ames is responsible for the ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed the Kepler mission development. Ball Aerospace & Technologies Corp. of Boulder, Colo., was responsible for developing the Kepler flight system. Ball and the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder are supporting mission operations. The California Institute of Technology in Pasadena manages JPL for NASA.

Ground observations necessary to confirm the discoveries were conducted with ground-based telescopes: the Keck I in Hawaii; Hobby-Ebberly and Harlan J. Smith 2.7m in Texas; Hale and Shane in California; WIYN, MMT and Tillinghast in Arizona; and Nordic Optical in the Canary Islands, Spain. For more information about the Kepler mission, visit http://www.nasa.gov/kepler .

Whitney Clavin 818-354-4673

Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241

Headquarters, Washington

j.d.harrington@nasa.gov

The Night Sky: January 2010

The Night Sky in January 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 15thFull "Wolf Moon" on the 30th

Stars and Constellations

Frosty January evenings provide a chance to become acquainted with the brilliant stars and constellations of winter, which are now in their full splendor. At the beginning of the month, though, you can catch a last look at the Summer Triangle stars Vega, Altair, and Deneb before they vanish below the northwestern horizon during the early evening. The remaining representatives of the autumn sky, including the Great Square of Pegasus and the "water" constellations of Pisces (the Fishes) and Cetus (the Whale), will also be setting in the west later in the evening. The rest of the night belongs to the stars of winter. The constellation Perseus is nearly overhead by 8 pm, just to the east of the upside-down "W" of Cassiopeia. To the east of Perseus is Auriga, the Charioteer, one of the brightest of winter constellations. Auriga represents the Greek mythological character Erichthonius, a lame man who invented the horse-drawn chariot so he could travel about. His "eye" is the bright star Capella, which means "little she-goat." Capella is the sixth brightest star in the sky, and is actually two stars very close together.

Just south of Auriga is Taurus, the Bull, which contains the bright orange giant star Aldebaran. Aldebaran is a red giant star 25 times larger than or Sun. By coincidence, Aldebaran is situated in the foreground of the Hyades star cluster; the two are unrelated, as Aldebaran lies at a distance of 65 light years from our solar system, while the Hyades group is over twice as far away. Taurus also contains the beautiful and compact star cluster the Pleiades, or Seven Sisters, which lies 440 light years away. Taurus is an ancient constellation, which in Greek mythology represents the Minotaur, a half-man, half-bull monster. Another Greek legend states that the Taurus represents the disguise which Zeus assumed in order to seduce the Phoenician king’s daughter, Europa. Yet another story equates Taurus with the Cretan bull tamed by Hercules as one of his twelve labors.

Just east of Taurus is Gemini, which contains the stars Pollux and Castor. The most famous of all the winter constellations is Orion, the Hunter, which stands high in the south around the midnight hour during January. All of Orion’s stars, including his two brightest, orange Betelgeuse and bluish Rigel, are hundreds of light years distant from our solar system. Orion is accompanied on the hunt by his two faithful dogs, Canis Major, the Big Dog, and Canis Minor, the Little Dog , to Orion’s upper and lower left, respectively. To Canis Major belongs the brightest star in the night sky, Sirius, the "Dog Star," which looks like a brilliant bluish-white beacon in the southeast during the evening hours of early winter. Look for Sirius as it rises at 7 pm at the beginning of January, but two hours earlier, or around sunset, by month's end. Canis Minor has his own bright star, Procyon, the "Pup." In contrast to the remote stars of Orion, both Sirius and Procyon are among the Sun’s closest neighbors in space, lying at distances of only 8 and 11 light years, respectively.

Naked-Eye Planets In the Evening and Morning Sky

Jupiter, which resembles a brilliant cream-colored star low in the southwest after darkness falls, has been a faithful beacon in the evening sky since last summer. Although still an impressive sight this January, Jupiter's duration in the night sky lessens as it continues to sink toward the southwestern horizon during the course of the month. On New Year’s Day, Jupiter sets by 8:30 pm, but by the 31st, it sets at 7 pm, or only about an hour and a half after sunset. By the end of February, Jupiter will be in conjunction with the Sun and unobservable.

Mars is at its best at the end of January, when it reaches opposition with the Sun and is closest to Earth. (The last time Mars was so favorably positioned was back in December 2007.) Early in the month, Mars rises at 7:30 pm, or about two and a half hours after sunset. By the end of the month, when opposition occurs, Mars rises as the Sun sets, shortly after 5 pm, remains in view all night long, and sets as the Sun rises. Mars resembles a bright orange star low in the northeast during the early evening hours, and gets higher as the night progresses, eventually transiting the meridian high in the south at midnight. A modest telescope should reveal some of the surface markings and polar caps. It is worth noting that Mars will have about the same brightness as the brightest star in the night sky, Sirius, which can easily be located below and to the left of Orion. The color contrast between orange Mars and blue-white Sirius is striking.

Of special note is the fact that during December Mars moved eastward from Cancer into Leo, following typical west-to-east orbital behavior, but this month it shifts westward back into Cancer. This phenomenon mystified ancient astronomers, including many of the Greeks, but today it is easily explained as a result of the Earth, as it orbits the Sun, overtaking and "passing" the more slowly traveling Mars in its outer orbit, thus giving the appearance of backwards motion.

Saturn, currently located among the stars of the constellation Virgo, becomes firmly established as an evening planet this month, rising around 11:30 pm at the beginning of the month and by 9:30 pm at month’s end. Look toward the east at least an hour or so after these times to find yellow Saturn with the blue-white star Spica not far below it. While not nearly as bright as Mars, Saturn is nevertheless worth finding; a telescope or even good binoculars will reveal the famous ring system.

Mercury is in conjunction with the Sun on the 4th, and therefore is not viewable during the first week or so of January. Shortly after conjunction, however, Mercury jumps into the early morning sky, rising nearly one and a half hours before the Sun for the second half of the month. It reaches greatest elongation with the Sun on the 27th. To spot Mercury, look for what appears to be a bright yellow star low in the south east about an hour before sunrise. The other inner planet, Venus, is in conjunction with the Sun on the 11th, and remains lost in the glare of the Sun until the end of February, when it will begin to appear in the evening sky.

Earth reaches perihelion, or closest approach to the Sun, on January 2, when it will be about 3.5% closer to the Sun than it was in July. Note that it is the tilt of Earth's axis, not its orbital eccentricity, which causes the seasons.

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

Keck Telescopes Gaze into Young Star's "Life Zone"

WASHINGTON, DC (Jan. 2, 2010) – The inner regions of young planet-forming disks offer information about how worlds like Earth form, but not a single telescope in the world can see them. Yet, for the first time, astronomers using the W. M. Keck Observatory in Hawaii have measured the properties of a young solar system at distances closer to the star than Venus is from our sun.

FIGURE CAPTION – Planets form around a young star in this artist's concept. Using the Keck Interferometer in Hawaii, astronomers have probed the structure of a dust disk around MWC 419 to within 50 million miles of the star. Credit: David A. Hardy/www.astroart.org

"When it comes to building rocky planets like our own, the innermost part of the disk is where the action is," said team member William Danchi at NASA's Goddard Space Flight Center in Greenbelt, Md. Planets forming in a star's inner disk may orbit within its "habitable zone," where conditions could potentially support the development of life.

To achieve the feat, the team used the Keck Interferometer to combine infrared light gathered by both of the observatory's twin 10-meter telescopes, which are separated by 85 meters. The double-barreled approach gives astronomers the effective resolution of a single 85-meter telescope -- several times larger than any now planned.

"Nothing else in the world provides us with the types of measurements the Keck Interferometer does," said Wesley Traub at Caltech's Jet Propulsion Laboratory in Pasadena, Calif. "In effect, it's a zoom lens for the Keck telescopes."

In August 2008, the team -- led by Sam Ragland of Keck Observatory and including astronomers from the California Institute of Technology and the National Optical Astronomical Observatory -- observed a Young Stellar Object (YSO) known as MWC 419. The blue, B-type star has several times the sun's mass and lies about 2,100 light-years away in the constellation Cassiopeia. With an age less than ten million years, MWC 419 ranks as a stellar kindergartener.

The team also employed a new near-infrared camera designed to image wavelengths in the so-called L band from 3.5 to 4.1 micrometers. "This unique infrared capability adds a new dimension to the Keck Interferometer in probing the density and temperature of planet-forming regions around YSO disks. This wavelength region is relatively unexplored," Ragland explained. "Basically, anything we see through this camera is brand new information."

The increased ability to observe fine detail, coupled with the new camera, let the team measure temperatures in the planet-forming disk to within about 50 million miles of the star. "That's about half of Earth's distance from the sun, and well within the orbit of Venus," Danchi said.

For comparison, the planets directly detected around the stars HR 8799, Fomalhaut and GJ 758 orbit between 40 and 100 times farther away.

The team reported temperature measurements of dust at various regions throughout MWC 419's inner disk in the Sept. 20 issue of The Astrophysical Journal. Temperature differences help shed light on the inner disk's detailed structure and may indicate that its dust has different chemical compositions and physical properties, factors that may play a role in the types of planets that form. For example, conditions in our solar system favored the formation of rocky worlds from Mars sunward, whereas gas giants and icy moons assembled farther out.

In turn, the astronomers note, the size of the young star might affect the composition and physical characteristics of its dust disk. The team is continuing to use the Keck Interferometer in a larger program to observe planet-forming disks around sun-like stars.

The Keck Interferometer was developed by the Jet Propulsion Laboratory and the W.M. Keck Observatory. It is managed by the W.M. Keck Observatory, which operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the island of Hawaii and is a scientific partnership of the California Institute of Technology, the University of California and NASA. NASA's Exoplanet Science Institute manages time allocation on the telescope for NASA.

Related links:

Keck Telescopes Take Deeper Look at Planetary Nurseries

Twin Keck Telescopes Probe Dual Dust Disks

Francis ReddyNASA's Goddard Space Flight Center

Talk: Collecting Meteorites in Antarctica (41 min)

Every year since the late 70's the US National Science Foundation has supported a team of space scientists to search for meteorites in Antarctica. Why Antarctica? The polar desert environment best preserves these precious samples of other worlds, which include shattered planetesimals, fragments of asteroids, and even rocks from the Moon and Mars. In this talk, I will discuss the scientific importance of meteorites, and the methods used to recover them from the East Antarctic Ice Sheet.

Dr. Kress was a member of the ANSMET 2003-04 Expedition. (ANSMET = Antarctic search for meteorites)
http://geology.cwru.edu/~ansmet/

Talk: Cassini Explores The Saturn System (74 min)

A glistening spaceship, with seven lonely years and billions of miles behind it, glides into orbit around a ringed, softly-hued planet. A flying-saucer shaped machine descends through a hazy atmosphere and lands on the surface of an alien moon, ten times farther from the Sun than the Earth.

Fantastic though they seem, these visions are not a dream. For seven years, the Cassini spacecraft and its Huygens probe traveled invisible interplanetary roads to the place we call Saturn. Their successful entry into orbit a thousand days ago, the mythic landing of Huygens on the cold, dark equatorial plains of Titan, and Cassini's subsequent explorations of the Saturn System.

Talk: Results of the Phoenix Mission to Mars (49 min)

Phoenix landed at 68N in the ice-rich ground on Mars and investigated the chemistry and geology of a polar site on Mars for the first time. The site is particularly interesting for astrobiology because 5 Myr ago the tilt of Mars' axis was 45 and the amount of sunlight reaching the Phoenix site at summer solstice is 2x the present value - Earth like levels. Understanding the microbial activity in high elevation dry permafrost in Antarctica provides a basis for considering habitability conditions on Mars during these periods of higher obliquity.

Speaker: Chris McKay, NASA Ames Research Center
Dr. Christopher P. McKay, Planetary Scientist with the Space Science Division of NASA Ames. Chris received his Ph.D. in AstroGeophysics from the University of Colorado in 1982 and has been a research scientist with the NASA Ames Research Center since that time. His current research focuses on the evolution of the solar system and the origin of life. He is also actively involved in planning for future Mars missions including human settlements. Chris has been involved with polar research since 1980, traveling to the Antarctic dry valleys and more recently to the Siberian and Canadian Arctic to conduct research in these Mars-like environments. Dr. McKay is a recepient of the prestigious Kuiper Award from the Division of Planetary Sciences of the American Astronomical Society for his contributions.

This Space Exploration series talk was hosted by Boris Debic.

Avatar's Moon Pandora Could Be Real

CAMBRIDGE, MA (Dec. 18, 2009) – In the new blockbuster Avatar, humans visit the habitable - and inhabited - alien moon called Pandora. Life-bearing moons like Pandora or the Star Wars forest moon of Endor are a staple of science fiction. With NASA's Kepler mission showing the potential to detect Earth-sized objects, habitable moons may soon become science fact. If we find them nearby, a new paper by Smithsonian astronomer Lisa Kaltenegger shows that the James Webb Space Telescope (JWST) will be able to study their atmospheres and detect key gases like carbon dioxide, oxygen, and water vapor.

FIGURE CAPTION – This artist's conception shows a hypothetical gas giant planet with an Earth-like moon similar to the moon Pandora in the movie Avatar. New research shows that, if we find such an "exomoon" in the habitable zone of a nearby star, the James Webb Space Telescope will be able to study its atmosphere and detect key gases like carbon dioxide, oxygen, and water. The key is to find a planet that transits its star, and then find a moon orbiting that planet more than one stellar radius away, so that the moon can be studied independently of the planet. Moreover, an alien moon orbiting the gas giant planet of a red dwarf star may be more likely to be habitable than tidally locked Earth-sized planets or super-Earths. Credit: David A. Aguilar, CfA

"If Pandora existed, we potentially could detect it and study its atmosphere in the next decade," said Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics (CfA).

So far, planet searches have spotted hundreds of Jupiter-sized objects in a range of orbits. Gas giants, while easier to detect, could not serve as homes for life as we know it. However, scientists have speculated whether a rocky moon orbiting a gas giant could be life-friendly, if that planet orbited within the star's habitable zone (the region warm enough for liquid water to exist).

"All of the gas giant planets in our solar system have rocky and icy moons," said Kaltenegger. "That raises the possibility that alien Jupiters will also have moons. Some of those may be Earth-sized and able to hold onto an atmosphere."

Kepler looks for planets that cross in front of their host stars, which creates a mini-eclipse and dims the star by a small but detectable amount. Such a transit lasts only hours and requires exact alignment of star and planet along our line of sight. Kepler will examine thousands of stars to find a few with transiting worlds.

Once they have found an alien Jupiter, astronomers can look for orbiting moons, or exomoons. A moon's gravity would tug on the planet and either speed or slow its transit, depending on whether the moon leads or trails the planet. The resulting transit duration variations would indicate the moon's existence.

Once a moon is found, the next obvious question would be: Does it have an atmosphere? If it does, those gases will absorb a fraction of the star's light during the transit, leaving a tiny, telltale fingerprint to the atmosphere's composition.

The signal is strongest for large worlds with hot, puffy atmospheres, but an Earth-sized moon could be studied if conditions are just right. For example, the separation of moon and planet needs to be large enough that we could catch just the moon in transit, while its planet is off to one side of the star.

Kaltenegger calculated what conditions are best for examining the atmospheres of alien moons. She found that alpha Centauri A, the system featured in Avatar, would be an excellent target.

"Alpha Centauri A is a bright, nearby star very similar to our Sun, so it gives us a strong signal" Kaltenegger explained. "You would only need a handful of transits to find water, oxygen, carbon dioxide, and methane on an Earth-like moon such as Pandora."

"If the Avatar movie is right in its vision, we could characterize that moon with JWST in the near future," she added.

While alpha Centauri A offers tantalizing possibilities, small, dim, red dwarf stars are better targets in the hunt for habitable planets or moons. The habitable zone for a red dwarf is closer to the star, which increases the probability of a transit.

Astronomers have debated whether tidal locking could be a problem for red dwarfs. A planet close enough to be in the habitable zone would also be close enough for the star's gravity to slow it until one side always faces the star. (The same process keeps one side of the Moon always facing Earth.) One side of the planet then would be baked in constant sunlight, while the other side would freeze in constant darkness.

An exomoon in the habitable zone wouldn't face this dilemma. The moon would be tidally locked to its planet, not to the star, and therefore would have regular day-night cycles just like Earth. Its atmosphere would moderate temperatures, and plant life would have a source of energy moon-wide.

"Alien moons orbiting gas giant planets may be more likely to be habitable than tidally locked Earth-sized planets or super-Earths," said Kaltenegger. "We should certainly keep them in mind as we work toward the ultimate goal of finding alien life."

For more information, contact:

Lisa Kaltenegger
617-495-7158
617-838-2808
lkaltene@cfa.harvard.edu

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Glint of Sunlight Confirms Liquid in Northern Lake District of Titan

PASADENA, CA (Dec. 17, 2009) – NASA's Cassini Spacecraft has captured the first flash of sunlight reflected off a lake on Saturn's moon Titan, confirming the presence of liquid on the part of the moon dotted with many large, lake-shaped basins.

Cassini scientists had been looking for the glint, also known as a specular reflection, since the spacecraft began orbiting Saturn in 2004. But Titan's northern hemisphere, which has more lakes than the southern hemisphere, has been veiled in winter darkness. The sun only began to directly illuminate the northern lakes recently as it approached the equinox of August 2009, the start of spring in the northern hemisphere. Titan's hazy atmosphere also blocked out reflections of sunlight in most wavelengths. This serendipitous image was captured on July 8, 2009, using Cassini's visual and infrared mapping spectrometer.

The new infrared image is available online at: http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and http://wwwvims.lpl.arizona.edu.

This image will be presented Friday, Dec. 18, at the fall meeting of the American Geophysical Union in San Francisco.

"This one image communicates so much about Titan -- thick atmosphere, surface lakes and an otherworldliness," said Bob Pappalardo, Cassini project scientist, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's an unsettling combination of strangeness yet similarity to Earth. This picture is one of Cassini's iconic images."

Titan, Saturn's largest moon, has captivated scientists because of its many similarities to Earth. Scientists have theorized for 20 years that Titan's cold surface hosts seas or lakes of liquid hydrocarbons, making it the only other planetary body besides Earth believed to harbor liquid on its surface. While data from Cassini have not indicated any vast seas, they have revealed large lakes near Titan's north and south poles.

In 2008, Cassini scientists using infrared data confirmed the presence of liquid in Ontario Lacus, the largest lake in Titan's southern hemisphere. But they were still looking for the smoking gun to confirm liquid in the northern hemisphere, where lakes are also larger.

Katrin Stephan, of the German Aerospace Center (DLR) in Berlin, an associate member of the Cassini visual and infrared mapping spectrometer team, was processing the initial image and was the first to see the glint on July 10th.

"I was instantly excited because the glint reminded me of an image of our own planet taken from orbit around Earth, showing a reflection of sunlight on an ocean," Stephan said. "But we also had to do more work to make sure the glint we were seeing wasn't lightning or an erupting volcano."

Team members at the University of Arizona, Tucson, processed the image further, and scientists were able to compare the new image to radar and near-infrared-light images acquired from 2006 to 2008.

They were able to correlate the reflection to the southern shoreline of a lake called Kraken Mare. The sprawling Kraken Mare covers about 400,000 square kilometers (150,000 square miles), an area larger than the Caspian Sea, the largest lake on Earth. It is located around 71 degrees north latitude and 337 degrees west latitude.

The finding shows that the shoreline of Kraken Mare has been stable over the last three years and that Titan has an ongoing hydrological cycle that brings liquids to the surface, said Ralf Jaumann, a visual and infrared mapping spectrometer team member who leads the scientists at the DLR who work on Cassini. Of course, in this case, the liquid in the hydrological cycle is methane rather than water, as it is on Earth.

"These results remind us how unique Titan is in the solar system," Jaumann said. "But they also show us that liquid has a universal power to shape geological surfaces in the same way, no matter what the liquid is."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.

Jia-Rui C. Cook 818-354-0850

Jet Propulsion Laboratory, Pasadena, Calif.

jia-rui.c.cook@jpl.nasa.gov

Suzaku Catches Retreat of a Black Hole's Disk

GREENBELT, MD (Dec. 8, 2009) – Studies of one of the galaxy's most active black-hole binaries reveal a dramatic change that will help scientists better understand how these systems expel fast-moving particle jets.

FIGURE CAPTION – GX 339-4, illustrated here, is among the most dynamic binaries in the sky, with four major outbursts in the past seven years. In the system, an evolved star no more massive than the sun orbits a black hole estimated at 10 solar masses. Credit: ESO/L. Calçada

Binary systems where a normal star is paired with a black hole often produce large swings in X-ray emission and blast jets of gas at speeds exceeding one-third that of light. What fuels this activity is gas pulled from the normal star, which spirals toward the black hole and piles up in a dense accretion disk.

"When a lot of gas is flowing, the dense disk reaches nearly to the black hole," said John Tomsick at the University of California, Berkeley. "But when the flow is reduced, theory predicts that gas close to the black hole heats up, resulting in evaporation of the innermost part of the disk." Never before have astronomers shown an unambiguous signature of this transformation.

To look for this effect, Tomsick and an international group of astronomers targeted GX 339-4, a low-mass X-ray binary located about 26,000 light-years away in the constellation Ara. There, every 1.7 days, an evolved star no more massive than the sun orbits a black hole estimated at 10 solar masses. With four major outbursts in the past seven years, GX 339-4 is among the most dynamic binaries in the sky.

In September 2008, nineteen months after the system's most recent outburst, the team observed GX 339-4 using the orbiting Suzaku X-ray observatory, which is operated jointly by the Japan Aerospace Exploration Agency and NASA. At the same time, the team also observed the system with NASA's Rossi X-ray Timing Explorer satellite.

Instruments on both satellites indicated that the system was faint but in an active state, when black holes are known to produce steady jets. Radio data from the Australia Telescope Compact Array confirmed that GX 339-4's jets were indeed powered up when the satellites observed.

Despite the system's faintness, Suzaku was able to measure a critical X-ray spectral line produced by the fluorescence of iron atoms. "Suzaku's sensitivity to iron emission lines and its ability to measure the shapes of those lines let us see a change in the accretion disk that only happens at low luminosities," said team member Kazutaka Yamaoka at Japan's Aoyama Gakuin University.

X-ray photons emitted from disk regions closest to the black hole naturally experience stronger gravitational effects. The X-rays lose energy and produce a characteristic signal. At its brightest, GX 339-4's X-rays can be traced to within about 20 miles of the black hole. But the Suzaku observations indicate that, at low brightness, the inner edge of the accretion disk retreats as much as 600 miles.

"We see emission only from the densest gas, where lots of iron atoms are producing X-rays, but that emission stops close to the black hole -- the dense disk is gone," explained Philip Kaaret at the University of Iowa. "What's really happening is that, at low accretion rates, the dense inner disk thins into a tenuous but even hotter gas, rather like water turning to steam."

The dense inner disk has a temperature of about 20 million degrees Fahrenheit, but the thin evaporated disk may be more than a thousand times hotter.

The study, which appears in the Dec. 10 issue of The Astrophysical Journal Letters, confirms the presence of low-density accretion flow in these systems. It also shows that GX 339-4 can produce jets even when the densest part of the disk is far from the black hole.

"This doesn't tell us how jets form, but it does tell us that jets can be launched even when the high-density accretion flow is far from the black hole," Tomsick said. "This means that the low-density accretion flow is the most essential ingredient for the formation of a steady jet in a black hole system."

Francis Reddy
NASA's Goddard Space Flight Center

'Our Place in the Cosmos'

"Our Place in the Cosmos", the third video from the Symphony of Science, was crafted using samples from Carl Sagan's Cosmos, Richard Dawkins' Genius of Charles Darwin series, Dawkins' TED Talk, Stephen Hawking's Universe series, Michio Kaku's interview on Physics and aliens, plus added visuals from Baraka, Koyaanisqatsi, History Channel's Universe series, and IMAX Cosmic Voyage. The themes present in this song are intended to explore our understanding of our origins within the universe, and to challenge the commonplace notion that humans have a superior or privleged position, both on our home planet and in the universe itself.

Enjoy!

John
john@symphonyofscience.com

RIP Dr. Sagan and Dr. Jastrow!

Lyrics:

[Narrator]
With every century
Our eyes on the universe have been opened anew
We are witness
To the very brink of time and space

[Robert Jastrow]
We must ask ourselves
We who are so proud of our accomplishments
What is our place in the cosmic perspective of life?

[Carl Sagan]
The exploration of the cosmos
Is a voyage of self discovery
As long as there have been humans
We have searched for our place in the cosmos

[Richard Dawkins]
Are there things about the universe
That will be forever beyond our grasp?
Are there things about the universe that are
Ungraspable?

[Sagan]
One of the great revelations of space exploration
Is the image of the earth, finite and lonely
Bearing the entire human species
Through the oceans of space and time

[Dawkins]
Matter flows from place to place
And momentarily comes together to be you
Some people find that thought disturbing
I find the reality thrilling

[Sagan]
As the ancient mythmakers knew
We're children equally of the earth and the sky
In our tenure on this planet, we've accumulated
Dangerous evolutionary baggage

We've also acquired compassion for others,
Love for our children,
And a great soaring passionate intelligence
The clear tools for our continued survival

[Michio Kaku]
We could be in the middle
Of an inter-galactic conversation
And we wouldn't even know

[Sagan]
We've begun at last
To wonder about our origins
Star stuff contemplating the stars
Tracing that long path

Our obligation to survive and flourish
Is owed not just to ourselves
But also to that cosmos
Ancient and vast, from which we spring

'We Are All Connected'

"We Are All Connected" was made from sampling Carl Sagan's Cosmos, The History Channel's Universe series, Richard Feynman's 1983 interviews, Neil deGrasse Tyson's cosmic sermon, and Bill Nye's Eyes of Nye Series, plus added visuals from The Elegant Universe (NOVA), Stephen Hawking's Universe, Cosmos, the Powers of 10, and more. It is a tribute to great minds of science, intended to spread scientific knowledge and philosophy through the medium of music.

Enjoy!

John
john@symphonyofscience.com

Lyrics:

[deGrasse Tyson]
We are all connected;
To each other, biologically
To the earth, chemically
To the rest of the universe atomically

[Feynman]
I think nature's imagination
Is so much greater than man's
She's never going to let us relax

[Sagan]
We live in an in-between universe
Where things change all right
But according to patterns, rules,
Or as we call them, laws of nature

[Nye]
I'm this guy standing on a planet
Really I'm just a speck
Compared with a star, the planet is just another speck
To think about all of this
To think about the vast emptiness of space
There's billions and billions of stars
Billions and billions of specks

[Sagan]
The beauty of a living thing is not the atoms that go into it
But the way those atoms are put together
The cosmos is also within us
We're made of star stuff
We are a way for the cosmos to know itself

Across the sea of space
The stars are other suns
We have traveled this way before
And there is much to be learned

I find it elevating and exhilarating
To discover that we live in a universe
Which permits the evolution of molecular machines
As intricate and subtle as we

[deGrasse Tyson]
I know that the molecules in my body are traceable
To phenomena in the cosmos
That makes me want to grab people in the street
And say, have you heard this??

(Richard Feynman on hand drums and chanting)

[Feynman]
There's this tremendous mess
Of waves all over in space
Which is the light bouncing around the room
And going from one thing to the other

And it's all really there
But you gotta stop and think about it
About the complexity to really get the pleasure
And it's all really there
The inconceivable nature of nature

A Star 200 Times as Massive as the Sun Goes Supernova

REHOVOT, ISRAEL (Dec. 4, 2009) – What happens when a really gargantuan star – one hundreds of times bigger than our sun – blows up? Although a theory developed years ago describes what the explosion of such an enormous star should look like, no one had actually observed one – until now.

FIGURE CAPTION – Kepler's supernova remnant. The explosion of a star is a catastrophic event. The blast rips the star apart and unleashes a roughly spherical shock wave that expands outward at more than 35 million kilometers per hour (22 million mph) like an interstellar tsunami. What might happen when a really gargantuan star -- one hundreds of times bigger than our sun -- blows up? (Credit: NASA)

An international team, led by scientists in Israel, and including researchers from Germany, the US, UK and China, tracked a supernova -- an exploding star -- for over a year and a half, and found that it neatly fits the predictions for the explosion of a star of over 150 times the sun's mass. Their findings, which could influence our understanding of everything from natural limits on star size to the evolution of the universe, appeared recently in Nature.

'It's all about balance,' says team leader Dr. Avishay Gal-Yam of the Particle Physics and Astrophysics Department. 'During a star's lifetime, there's a balance between the gravity that pulls its material inward and the heat produced in the nuclear reaction at its core, pushing it out. In a supernova we're familiar with, of a star 10 -100 times the size of the sun, the nuclear reaction begins with the fusion of hydrogen into helium, as in our sun. But the fusion keeps going, producing heavier and heavier elements, until the core turns to iron. Since iron doesn't fuse easily, the reaction burns out, and the balance is lost. Gravity takes over and the star collapses inward, throwing off its outer layers in the ensuing shockwaves.'

The balance in a super-giant star is different. Here, the photons (light particles) are so hot and energetic, they interact to produce pairs of particles: electrons and their opposites, positrons. In the process, particles with mass are created from the mass-less photons, and this consumes the star's energy. Again, things are thrown out of balance, but this time, when the star collapses, it falls in on a core of volatile oxygen, rather than iron. The hot, compressed oxygen explodes in a runaway thermonuclear reaction that obliterates the star's core, leaving behind little but glowing stardust. 'Models of 'pair supernovae' had been calculated decades ago,' says Gal-Yam, 'but no one was sure these huge explosions really occur in nature. The new supernova we discovered fits these models very well.'

An analysis of the new supernova data led the scientists to estimate the star's size at around 200 times the mass of the sun. This in itself is unusual, as observers had noted that the stars in our part of the universe seem to have a size limit of about 150 suns; some had even wondered if there was some sort of physical constraint on a star's girth. The new findings suggest that hyper-giant stars, while rare, do exist, and that even larger stars, up to 1000 times the size of the sun, may have existed in the early universe. 'This is the first time we've been able to analyze observations of such a massive exploding star,' says Dr. Paolo Mazzali of the Max Planck Institute for Astrophysics, Germany, who led the theoretical study of this object. 'We were able to measure the amounts of new elements created in this explosion, including approximately five times the mass of our sun in highly radioactive, freshly synthesized nickel. Such explosions may be important factories for heavy metals in the Universe.'

This massive supernova was found in a tiny galaxy -- only a hundredth the size of our own, and the scientists think that such dwarf galaxies could be natural harbors for the giant stars, somehow enabling them to surpass the 150 sun limit.

'Our discovery and analysis of this unique explosion has given us new insights into just how massive stars can get and how these stellar giants contribute to the makeup of our Universe', says Dr. Gal-Yam.'We hope to understand even more when we find additional examples from new surveys that we have recently begun to carry out, covering large, previously unexplored areas of the Universe.'

Dr. Avishai Gal-Yam's research is supported by the Nella and Leon Benoziyo Center for Astrophysics; the Peter and Patricia Gruber Awards;William Z. & Eda Bess Novick New Scientists Fund; the Legacy Heritage Fund Program of the Israel Science Foundation; and Miel de Botton Aynsley, UK.

Kuiper Belt

Kuiper Belt:

In 1950, Dutch astronomer Jan Oort proposed that certain comets came from a vast spherical shell of icy bodies near the edge of the Solar System. This giant swarm of objects is now named the Oort Cloud, occupying space at a distance between 5,000 and 100,000 astronomical units. (One astronomical unit, or AU, is the mean distance of Earth from the Sun: about 150 million kilometers or 93 million miles.)

The Oort Cloud contains billions of icy bodies in solar orbit. Occasionally, passing stars disturb the orbit of one of these bodies, causing it to come streaking into the inner solar system as a long-period comet. These comets have very large orbits and are observed in the inner solar system only once. In contrast, short-period comets take less than 200 years to orbit the Sun and they travel along the plane in which most of the planets orbit. They come from a region beyond Neptune called the Kuiper Belt, named for astronomer Gerard Kuiper, who proposed its existence in 1951.

The Kuiper Belt, extending out to about 50 AU around the Sun, is populated with thousands of small icy bodies.

Credit: NASA, ESA, and A. Feild [STScI

]In 1992, astronomers detected a reddish speck about 42 AU from the Sun-- the first time a Kuiper Belt object (or KBO for short) had been sighted. More than 1,000 KBOs have been identified since 1992. (They are sometimes called Edgeworth Kuiper Belt objects, acknowledging another astronomer who also is credited with the idea, or they are simply called Trans-Neptunian Objects (TNOs.)

The IAU has been the arbiter of planetary and satellite nomenclature since its inception in 1919. The various IAU Working Groups normally handle this process, and their decisions primarily affect the professional astronomers. But from time to time the IAU takes decisions and makes recommendations on issues concerning astronomical matters affecting other sciences or the public. Such decisions and recommendations are not enforceable by any national or international law; rather they establish conventions that are meant to help our understanding of astronomical objects and processes. Hence, IAU recommendations should rest on well-established scientific facts and have a broad consensus in the community concerned.

Quaoar Compared by Diameter with Other Solar System Bodies

The boundary between (major) planet and minor planet has never been defined and the recent discovery of other "Trans-Neptunian Objects" (TNOs), including some larger than Pluto, triggered the IAU to form a Working Group on "Definition of a Planet" from its Division III members.

Quaoar and Orcus

One of the largest KBOs is Quaoar (2002 LM60), named by its discoverers after the mythical creation-force figure of the Tongva tribe of the Los Angeles basin. Quaoar orbits the Sun every 288 years about a billion miles beyond the orbit of Pluto (somewhere around 42 AU). Quaoar was photographed in 1980, but was not recognized as a KBO until 2002, by Astronomer Mike Brown and his colleagues at Caltech in Pasadena, California.

Quaoar is about 1250 km in diameter, roughly the size of Pluto's moon Charon. Nothing larger has been found in our solar system since Pluto was discovered in 1930 (and Pluto's moon Charon in 1978). It's huge. In fact, if you took the 50,000 numbered asteroids and put them together, it would be about the same volume as Quaoar.

An even larger KBO (2004 DW, now officially named Orcus) was found at a distance of about 45 AU from the Sun.

2005 FY9, codenamed "Easterbunny," is a very large Kuiper belt object discovered on March 31, 2005 by the team led by Mike Brown at Caltech. Its discovery was announced on July 29, 2005 on the same day as two other very large trans-Neptunian objects (TNOs), 2003 EL61 and 2003 UB313, now officially known as Eris.

2005 FY9

2003 EL61

2005 FY9 is still awaiting its official name by the IAU. Detected by the Spitzer Space Telescope, initial estimates gave 2005 FY9 a diameter of 50% to 75% that of Pluto. It is similar in size to 2003 EL61, although somewhat brighter. This makes it the largest known Kuiper belt object after 2003 UB313 and Pluto.

The object orbits the Sun every 308 years. Like Pluto's, its orbit is somewhat eccentric and inclined.

2003 EL61

2003 EL61 is yet another object in the Kuiper Belt, discovered by Mike Brown and his team at Caltech. EL61 is also located in the region of space beyond Neptune that includes Pluto and the large planetoids Quaoar and Orcus, 2005 FY9, and the planet 2003 UB313, among others. 2003 EL61 is currently the third brightest object in this region after Pluto and 2005 FY9. It is so bright that it can readily be seen by high-end amateur telescopes equipped with CCD cameras. Other than being extremely bright, 2003 EL61 appeared at first to be typical of a type of Kuiper belt objects that astronomers call "scattered Kuiper belt objects." They are called "scattered" because it is believed that they once had a close encounter with Neptune, which gravitationally "scattered" these objects onto more eccentric orbits. The mass of 2003 EL61 is about 32% that of Pluto.

Artist's concept of Sedna

Sedna

In March 2004, a team of astronomers announced the discovery of a planet-like object, or planetoid, orbiting the Sun at an extreme distance, in the coldest known region of our solar system. Mike Brown, along with Doctors Chad Trujillo of the Gemini Observatory in Hawaii and David Rabinowitz of Yale University, New Haven, Conn., originally found the "planetoid" on November 14, 2003, using the 48-inch Samuel Oschin Telescope at Caltech's Palomar Observatory near San Diego. Within days, the object was observed by telescopes in Chile, Spain, Arizona and Hawaii, and soon after, NASA's new Spitzer Space Telescope looked for it.

The planetoid (2003 VB12), since named Sedna for an Inuit goddess who lives at the bottom of the frigid Arctic ocean, approaches the Sun only briefly during its 10,500-year solar orbit. Sedna is about one-quarter to three-eighths the size of the planet Pluto. At the farthest point in its long, elliptical orbit, Sedna is 130 billion kilometers (84 billion miles) from the Sun - that's about 86 AU, compared with the mean distances of Neptune (about 30 AU) and Pluto (about 39 AU).

Artist's concept of the view from Sedna, looking back toward the distant sun.

The discoverers of Sedna describe it as an inner Oort Cloud object, because it never enters the Kuiper Belt. Sedna never comes closer to the Sun than 76 AU. Sedna is quite an oddity: nobody expected to find an object like it in the largely empty space between the Kuiper Belt and the Oort Cloud. Possibly the Oort Cloud extends much farther in toward the Sun than previously thought, or perhaps Sedna is yet another type of object from the very early solar system, trapped between the Kuiper Belt and the Oort Cloud. Other notable features of Sedna include its size and reddish color; it is the second reddest object in the solar system, after Mars. At an estimated size of three-fourths the size of Pluto, it is likely the largest object found in the solar system since Pluto was discovered in 1930. Sedna lies extremely far from the Sun, in the coldest known region of our solar system, where the temperature never rises above minus 240 degrees Celsius (minus 400 Fahrenheit).

The KBO is usually even colder because it approaches the Sun this closely only briefly during its 10,500 year orbit around the Sun. At its most distant, "Sedna" is 130 billion kilometers (84 billion miles) from the Sun. That is 900 times Earth's distance from the Sun.

Scientists used the fact that even the Spitzer telescope was unable to detect the heat of the extremely distant, cold object to determine that it must be no more than 1,700 kilometers (about 1,000 miles) in diameter, smaller than Pluto. By combining all available data, Brown estimates the size at about halfway between that of Pluto and Quaoar, the planetoid discovered by the same team in 2002. Until "Sedna" was detected, Quaoar was the largest known body beyond Pluto.

Because KBOs are so distant, their sizes are difficult to measure. The given diameter of a KBO depends on assumptions about how its brightness relates to its size. To estimate size based on brightness, one assumes what percentage of sunlight the object's surface reflects; this percentage is known as the albedo. Thinking that the albedo of an average KBO is similar to that of comets, astronomers calculated the sizes of KBOs based on the reflectivity of comets, which is about 4 percent. An efficient way to calculate an object's albedo is to measure the heat it radiates in the infrared. In 2004, astronomers using the Spitzer Space Telescope did a survey of KBOs at infrared wavelengths and found that they averaged about 12 percent; thus, KBOs might be smaller objects than astronomers originally thought. However, new discoveries may alter this perception.

First Direct Observation of a Planet-like Object Orbiting a Star Similar to the Sun.

PRINCETON, NJ (Dec. 3, 2009) – An international team of scientists that includes an astronomer from Princeton University has made the first direct observation of a planet-like object orbiting a star similar to the sun.

The finding marks the first discovery made with the world's newest planet-hunting instrument on the Hawaii-based Subaru Telescope and is the first fruit of a novel research collaboration announced by the University in January.

The object, known as GJ 758 B, could be either a large planet or a "failed star," also known as a brown dwarf. The faint companion to the sun-like star GJ 758 is estimated to be 10 to 40 times as massive as Jupiter and is a "near neighbor" in our Milky Way galaxy, hovering a mere 300 trillion miles from Earth.

"It's a groundbreaking find because one of the current goals of astronomy is to directly detect planet-like objects around stars like our sun," said Michael McElwain, a postdoctoral research fellow in Princeton's Department of Astrophysical Sciences who was part of the team that made the discovery. "It is also an important verification that the system -- the telescope and its instruments -- is working well."

Images of the object were taken in May and August during early test runs of the new observation equipment. The team has members from Princeton, the University of Hawaii, the University of Toronto, the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and the National Astronomical Observatory of Japan (NAOJ) in Tokyo. The results were released online Nov. 18 in an electronic version of the Astrophysical Journal Letters.

"This challenging but beautiful detection of a very low mass companion to a sun-like star reminds us again how little we truly know about the census of gas giant planets and brown dwarfs around nearby stars," said Alan Boss, an astronomer at the Carnegie Institution for Science in Washington, D.C., who was not involved in the research. "Observations like this will enable theorists to begin to make sense of how this hitherto unseen population of bodies was able to form and evolve."

Brown dwarfs are stars that are not massive enough to sustain fusion reactions at their core, so they burn out and cool off as they age.

Aided by new varieties of viewing techniques, scientists started finding extrasolar planets (planets beyond the solar system) in 1992 and have located more than 400 planet-like objects so far. Most, however, have not been directly observed, but inferred from viewing the star around which the planet orbits. GJ 758 B is one of the first planet-like objects to be directly seen. Of the others that have been directly viewed, most have been on larger orbits than the distance between GJ 758 B and its star, or around stars with temperatures far above the average temperature of GJ 758 or our sun.

Scientists were able to spot the object even though it was hidden in the glare of the star it orbits by subtracting out that brighter light. To do this, they used the High Contrast Coronagraphic Imager with Adaptive Optics that has been attached to the Subaru Telescope. Also known as HiCIAO, it is part of a new generation of instruments specially made to detect faint objects near a bright star by masking its far more intense light. They also employed a technique known as angular differential imaging to capture the images.

"It's amazing how quickly this instrument has come online and burst into the forefront," said Marc Kuchner, an exoplanet scientist at the NASA Goddard Space Flight Center in Greenbelt, Md., who was not involved in the work. "I think this is just the beginning of what HiCIAO is going to do for the field." He added that the discovery also emphasizes that this new method of finding exoplanets -- direct detection -- is "really hitting its stride."

The planet-like object is currently at least 29 times as far from its star as the Earth is from the sun, approximately as far as Neptune is from the sun. However, further observations will be required to determine the actual size and shape of its orbit. At a temperature of only 600 F, the object is relatively "cold" for a body of its size. It is the coldest companion to a sun-like star ever recorded in an image.

The fact that such a large planet-like object appears to orbit at this location defies traditional thinking on planet formation. It is thought most larger planets are formed either closer to or farther from stars, but not in the location where GJ 758 is now. Discoveries such as this one could help theorists refine their ideas.

Telescope images also revealed a second companion to the star, which the scientists have called GJ 758 C. More observations, however, are needed to confirm whether it is nearby or just looks that way. "It looks very promising," said Christian Thalmann, one of the team's lead scientists. If it should turn out to be a second companion, he said, that would make both B and C more likely to be young planets rather than old brown dwarfs, since two brown dwarfs in such close proximity would not remain stable for such a long period of time.

Researchers from Princeton and NAOJ announced an agreement on Jan. 15 to collaborate over the next 10 years, using new equipment on the Subaru Telescope to peer into hidden corners of the nearby universe and ferret out secrets from its distant past. This research is a part of that collaboration. The HiCIAO team is led by Professor Motohide Tamura of NAOJ.

The partnership, called the NAOJ-Princeton Astrophysics Collaboration or N-PAC, provides for the exchange of scientific resources and supports a variety of long-term research projects in which the scientists from both Princeton and the Japanese astronomical community will participate on an equal basis. The collaboration builds on a decades-long tradition of scientific collaboration between Japanese and Princeton astronomers in a wide range of astronomical fields.

An important part of that partnership is the search for planets, previously hidden by the glare of stars. Finding these planets is a crucial step in answering the age-old question of the existence of extraterrestrial life.

The Subaru Telescope, whose name is the Japanese word for the Pleiades star cluster, is one of the largest telescopes in the world. The 8.2-meter optical infrared telescope is located on the summit of Mauna Kea, a dormant volcano in Hawaii. The isolated peak protrudes above most of the Earth's weather, making the site one of the best on the planet for astronomical observing. The telescope is owned and operated by NAOJ.

Comets

Throughout history, people have been both awed and alarmed by comets, stars with "long hair" that appeared in the sky unannounced and unpredictably. We now know that comets are dirty-ice leftovers from the formation of our solar system around 4.6 billion years ago. They are among the least-changed objects in our solar system and, as such, may yield important clues about the formation of our solar system. We can predict the orbits of many of them, but not all.

Around a dozen "new" comets are discovered each year. Short-period comets are more predictable because they take less than 200 years to orbit the Sun. Most come from a region of icy bodies beyond the orbit of Neptune. These icy bodies are variously called Kuiper Belt Objects, Edgeworth-Kuiper Belt Objects, or trans-Neptunian objects. Less predictable are long-period comets, many of which arrive from a distant region called the Oort cloud about 100,000 astronomical units (that is, 100,000 times the mean distance between Earth and the Sun) from the Sun. These comets can take as long as 30 million years to complete one trip around the Sun. (It takes Earth only 1 year to orbit the Sun.) As many as a trillion comets may reside in the Oort cloud, orbiting the Sun near the edge of the Sun's gravitational influence.

Each comet has only a tiny solid part, called a nucleus, often no bigger than a few kilometers across. The nucleus contains icy chunks and frozen gases with bits of embedded rock and dust. At its center, the nucleus may have a small, rocky core.

As a comet nears the Sun, it begins to warm up. The comet gets bright enough to see from Earth while its atmosphere - the coma - grows larger. The Sun's heat causes ice on the comet's surface to change to gases, which fluoresce like a neon sign. "Vents" on the Sun-warmed side may release fountains of dust and gas for tens of thousands of kilometers. The escaping material forms a coma that may be hundreds of thousands of kilometers in diameter.

The pressure of sunlight and the flow of electrically charged particles, called the solar wind, blow the coma materials away from the Sun, forming the comet's long, bright tails, which are often seen separately as straight tails of electrically charged ions and an arching tail of dust. The tails of a comet always point away from the Sun.

Most comets travel a safe distance from the Sun itself. Comet Halley comes no closer than 89 million kilometers from the Sun, which is closer to the Sun than Earth is. However, some comets, called sun-grazers, crash straight into the Sun or get so close that they break up and vaporize.

Impacts from comets played a major role in the evolution of the Earth, primarily during its early history billions of years ago. Some believe that they brought water and a variety of organic molecules to Earth.

Exoplanet Albedo

Mars, Jupiter, and all the other planets and asteroids in the night sky that are visible to us can be seen because they reflect sunlight. The "albedo" is the quantity that quantifies a body's ability to reflect light; a value of one indicates that all of the incident light on the body is reflected. Each body has a unique surface composition and atmosphere that reflect light in their own ways. For example, the presence of clouds in a planet's atmosphere can make it highly reflective. All these and other important physical properties contribute to the albedo, making the albedo one of the key properties of a planet.

There are 307 extrasolar planets (also called "exoplanets") known to date, but until now none of them has a known albedo. Astronomers can determine the radii and masses of exoplanets from precise observations of their orbital motions, but because the reflected starlight is only about one hundredth of one percent of the star's direct flux, even for a Jupiter-sized planet, the task of measuring the albedo is daunting.

Four CfA astronomers, Matt Holman, Jose Fernandez, David Latham, and David Charbonneau, together with four of their colleagues, have just reported the first precisely measured upper limit to the albedo of an extrasolar planet: TrES-3, a 1.9-Jupiter-mass body orbiting a sun-like star at a distance less than the distance between Mercury and the sun. TrES-3 has an orbital inclination to our line-of-sight that happens to make it cross the face of its star (an occultation). The team watched six occultations of the planet using only small, ground-based telescopes. By precisely measuring the flux changes at three wavelengths, they were able to set useful upper limits to the planet's albedo at these three wavelengths -- and the data show that clouds probably do not exist in the planet's upper atmosphere. The results not only provide the first meaningful measurement of an exoplanet's albedo, they demonstrate that relatively small telescopes can, with patience and care, infer many key properties of distant planets around other stars.

Large Hadron Collider Sets New World Record

GENEVA, SWITZERLAND (Dec. 2, 2009) – CERN's Large Hadron Collider has today become the world’s highest energy particle accelerator, having accelerated its twin beams of protons to an energy of 1.18 TeV in the early hours of the morning. This exceeds the previous world record of 0.98 TeV, which had been held by the US Fermi National Accelerator Laboratory’s Tevatron collider since 2001. It marks another important milestone on the road to first physics at the LHC in 2010.

“We are still coming to terms with just how smoothly the LHC commissioning is going,” said CERN Director General Rolf Heuer. “It is fantastic. However, we are continuing to take it step by step, and there is still a lot to do before we start physics in 2010. I’m keeping my champagne on ice until then.”

These developments come just 10 days after the LHC restart, demonstrating the excellent performance of the machine. First beams were injected into the LHC on Friday 20 November. Over the following days, the machine’s operators circulated beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV, gradually increasing the beam lifetime to around 10 hours. On Monday 23 November, two beams circulated together for the first time, and the four big LHC detectors recorded their first collision data.

Last night’s achievement brings further confirmation that the LHC is progressing smoothly towards the objective of first physics early in 2010. The world record energy was first broken yesterday evening, when beam 1 was accelerated from 450 GeV, reaching 1050 GeV (1.05 TeV) at 21:48, Sunday 29 November. Three hours later both LHC beams were successfully accelerated to 1.18 TeV, at 00:44, 30 November.

“I was here 20 years ago when we switched on CERN’s last major particle accelerator, LEP,” said Accelerators and Technology Director Steve Myers. “I thought that was a great machine to operate, but this is something else. What took us days or weeks with LEP, we’re doing in hours with the LHC. So far, it all augurs well for a great research programme.”

Next on the schedule is a concentrated commissioning phase aimed at increasing the beam intensity before delivering good quantities of collision data to the experiments before Christmas. So far, all the LHC commissioning work has been carried out with a low intensity pilot beam. Higher intensity is needed to provide meaningful proton-proton collision rates. The current commissioning phase aims to make sure that these higher intensities can be safely handled and that stable conditions can be guaranteed for the experiments during collisions. This phase is estimated to take around a week, after which the LHC will be colliding beams for calibration purposes until the end of the year.

First physics at the LHC is scheduled for the first quarter of 2010, at a collision energy of 7 TeV (3.5 TeV per beam).

Follow LHC progress on twitter at www.twitter.com/cern
For photos, video and latest information see: http://press.web.cern.ch/press/lhc-first-physics/ (Video regarding this event will be available during the day.)
Contact : http://press.web.cern.ch/press/ContactUs.html

Mars Rovers Missions 2003

In the summer of 2003 NASA'S Jet Propulsion Laboratory (JPL) Delivered to exploration rovers to the surface of the Red Planet. Watch how rovers landed there, and how they'r still exploring different regions of Mars still today.

The Night Sky: December 2009

The Night Sky in December 2009

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases in Month
Full Moon on the 2nd and on the 31stNew Moon on the 16th

The Full Moon in December is appropriately referred to as the "Cold" Moon. It has also been called the "Full Moon before Yule." This month, there are two Full Moons, and so the second one, which falls closest to the winter solstice (when days are shortest) is designated "The Long Night Moon." The second Full Moon in any month is also often referred to as the "Blue Moon."

Stars and Constellations

The Sun reaches the southernmost position on its apparent annual path, the ecliptic, through the zodiac constellations on December 21st at 12:47 pm, thus marking the beginning of winter in the northern hemisphere. Paradoxically, the trio of stars comprising the "summer" triangle – Vega, Deneb, and Altair – is still viewable low in the western sky shortly after it gets dark. The stars of autumn dominate the early evening sky, and one of the most familiar beacons of autumn nights, the white star Fomalhaut, is now getting low in the southwest. Fomalhaut and Vega lie at approximately the same distance: 25 light years. High above Fomalhaut, also toward the southwest, is the box of four stars comprising the Great Square of Pegasus. High in the north is the constellation Cassiopeia, now looking like the letter "M." Cassiopeia is followed in the northeast by the constellation Perseus.

Located nearly overhead during the early evening hours of December are two moderately faint constellations from antiquity. One is famous, the other not. Aries, the Ram, lies just to the east of Pisces and the Great Square. Aries originally represented the first constellation of the zodiac, because two millenia ago it contained the Vernal Equinox, the point through which the Sun passes annually, marking the first day of Spring in the northern hemisphere. Due to precession, a wobble of the Earth’s axis, the Vernal Equinox has since shifted westward into neighboring Pisces. Today, the Sun passes through the constellation Aries between April 19 and May 13. In ancient mythology, Aries was the source of the Golden Fleece that was sought by Jason and the Argonauts.

Just above Aries is Triangulum, a tiny constellation (size ranking 78th out of 88) consisting of three stars in a narrow triangle. One legend says that Triangulum represents a wedding gift to Proserpina, daughter of Ceres, upon her marriage to Pluto, God of the Underworld. Triangulum is noteworthy to astronomers because it contains M33, the "Pinwheel Galaxy." M33 lies at a distance of over 2 million light years, which makes it (along with the larger and more famous Great Galaxy in Andromeda) one of the nearest spiral galaxies to our own Milky Way.

By about 9 pm, the brilliant star groups of winter can be seen rising in the east. The first star of winter to catch your eye will probably be Capella, the yellow-white star in the constellation Auriga, the Charioteer, as it ascends in the northeast. Looking high in the east, to the right of Auriga, you can find the stars of Taurus, the Bull, which contains the bright reddish star Aldebaran. Aldebaran appears to be part of a "V" shaped cluster of stars known as the Hyades. Also part of Taurus is the Pleiades, a compact star cluster shaped like a miniature dipper. Each of those apparently dim stars of the Pleiades is intrinsically several hundred times more luminous than our Sun, but appears so faint because of its immense distance of over 400 light years from our solar system. At that distance, the light from the Pleiades which you see tonight has been traveling since the days of Shakespeare and Galileo. The undisputed champion of winter constellations is Orion, which contains two very bright stars, reddish Betelgeuse and bluish-white Rigel. By midnight, Orion is high in the south, and is sure to catch your attention if you are going out for midnight service on Christmas Eve. Located in the east-northeast between Auriga and Orion are the twin stars Pollux and Castor in the constellation Gemini. Rising not far to the right of this pair is Procyon, a yellow-white star in the constellation of Canis Minor. After about 9 pm, look toward the southeast, below Rigel, and you will see the brightest star in the night sky: bluish-white Sirius, the "dog star" in the constellation Canis Major.

Naked-Eye Planets In the Evening and Morning Sky

Mercury makes an especially good appearance in the evening sky for much of this month. It reaches its greatest elongation with the Sun on the 18th, and sets nearly an hour and a half after sunset on that date. To spot it, look for what appears to be a bright yellow star low in the southwest about a half-hour to an hour after sunset. Not far from Mercury, but higher up, is the much brighter Jupiter, which remains dominant in the evening sky during December. You cannot miss Jupiter: it resembles a brilliant cream-colored star in the southwest during the early evening hours. Jupiter lies nearly on the meridian (due south) at sunset at the beginning of the month, and sets after around 10 pm. By New Year’s Eve night, it sets at 8:30 pm.

As Jupiter is setting in the southwest, Mars is rising in the opposite part of the sky. Look for a bright orange-red object low in the northeast and getting higher as the night progresses. Mars moves from Cancer into Leo this month, and continues to get brighter as the distance between it and Earth decreases. Mars rises around 9:30 pm EST at the start of December and by a little after 7:30 pm at month's end. By the pre-dawn hours, Mars will be located high above the western horizon. Note that Mars reaches opposition with the Sun (and its closest approach to Earth) late next month, and its red glow will be a beautiful sight against the cold winter night sky.

Having spent the past several months in the early morning sky, Saturn has been slowly but surely working its way into the evening sky, and this month will begin to rise before midnight. At the beginning of December, Saturn rises at about 1:30 am and on the 31th by around 11:30 pm. Look above the eastern horizon to spot yellow Saturn with the blue-white star Spica not far away. A telescope will display the famous ring system, tilted nearly edge-on. By dawn, Saturn is nearly due south on the meridian.

Venus rises less than an hour before sunrise at the beginning of December, but that time interval shrinks rapidly, so that Venus is essentially lost in the Sun's glare for most of the month. Venus will be in conjunction with the Sun in January 2010, after which it will slowly reappear in the evening sky during the spring.

The Geminid Shower is expected to reach its peak on the nights of December 13th and 14th. Meteor streaks result as Earth passes through the debris from the asteroid 3200 Phaethon. As the mostly sand-grain sized particles enter Earth’s atmosphere at enormous speeds, several tens of kilometers per second, they are incinerated by friction with the surrounding air, resulting in bright trails across the sky.

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

Fermi Telescope Peers Deep into Microquasar

GREENBELT, MD (Dec. 1, 2009) – NASA's Fermi Gamma-ray Space Telescope has made the first unambiguous detection of high-energy gamma-rays from an enigmatic binary system known as Cygnus X-3. The system pairs a hot, massive star with a compact object -- either a neutron star or a black hole -- that blasts twin radio-emitting jets of matter into space at more than half the speed of light.

FIGURE CAPTION – In Cygnus X-3, an accretion disk surrounding a black hole or neutron star orbits close to a hot, massive star. Gamma rays (purple, in this illustration) likely arise when fast-moving electrons above and below the disk collide with the star's ultraviolet light. Fermi sees more of this emission when the disk is on the far side of its orbit. Credit: NASA's Goddard Space Flight Center

Astronomers call these systems microquasars. Their properties -- strong emission across a broad range of wavelengths, rapid brightness changes, and radio jets -- resemble miniature versions of distant galaxies (called quasars and blazars) whose emissions are thought to be powered by enormous black holes.

"Cygnus X-3 is a genuine microquasar and it's the first for which we can prove high-energy gamma-ray emission," said Stéphane Corbel at Paris Diderot University in France.

The system, first detected in 1966 as among the sky's strongest X-ray sources, was also one of the earliest claimed gamma-ray sources. Efforts to confirm those observations helped spur the development of improved gamma-ray detectors, a legacy culminating in the Large Area Telescope (LAT) aboard Fermi.

At the center of Cygnus X-3 lies a massive Wolf-Rayet star. With a surface temperature of 180,000 degrees F, or about 17 times hotter than the sun, the star is so hot that its mass bleeds into space in the form of a powerful outflow called a stellar wind. "In just 100,000 years, this fast, dense wind removes as much mass from the Wolf-Rayet star as our sun contains," said Robin Corbet at the University of Maryland, Baltimore County.

Every 4.8 hours, a compact companion embedded in a disk of hot gas wheels around the star. "This object is most likely a black hole, but we can't yet rule out a neutron star," Corbet noted.

Fermi's LAT detects changes in Cygnus X-3's gamma-ray output related to the companion's 4.8-hour orbital motion. The brightest gamma-ray emission occurs when the disk is on the far side of its orbit. "This suggests that the gamma rays arise from interactions between rapidly moving electrons above and below the disk and the star's ultraviolet light," Corbel explained.

When ultraviolet photons strike particles moving at an appreciable fraction of the speed of light, the photons gain energy and become gamma rays. "The process works best when an energetic electron already heading toward Earth suffers a head-on collision with an ultraviolet photon," added Guillaume Dubus at the Laboratory for Astrophysics in Grenoble, France. "And this occurs most often when the disk is on the far side of its orbit."

Through processes not fully understood, some of the gas falling toward Cygnus X-3's compact object instead rushes outward in a pair of narrow, oppositely directed jets. Radio observations clock gas motion within these jets at more than half the speed of light.

Between Oct. 11 and Dec. 20, 2008, and again between June 8 and Aug. 2, 2009, Cygnus X-3 was unusually active. The team found that outbursts in the system's gamma-ray emission preceded flaring in the radio jet by roughly five days, strongly suggesting a relationship between the two.

The findings, published today in the electronic edition of Science, will provide new insight into how high-energy particles become accelerated and how they move through the jets.

Related Links:

› Fermi Telescope Caps First Year With Glimpse of Space-Time
› Gamma-Rays from High-Mass X-Ray Binaries

Francis Reddy
NASA's Goddard Space Flight Center

Black hole zapping a galaxy into existence

GARCHING, GERMANY (Nov. 30, 2009) – Which comes first, the supermassive black holes that frantically devour matter or the enormous galaxies where they reside? A brand new scenario has emerged from a recent set of outstanding observations of a black hole without a home: black holes may be “building” their own host galaxy. This could be the long-sought missing link to understanding why the masses of black holes are larger in galaxies that contain more stars.

FIGURE CAPTION – This artist’s impression shows how jets from supermassive black holes could form galaxies, thereby explaining why the mass of black holes is larger in galaxies that contain more stars.

“The ‘chicken and egg’ question of whether a galaxy or its black hole comes first is one of the most debated subjects in astrophysics today,” says lead author David Elbaz. “Our study suggests that supermassive black holes can trigger the formation of stars, thus ‘building’ their own host galaxies. This link could also explain why galaxies hosting larger black holes have more stars.”

To reach such an extraordinary conclusion, the team of astronomers conducted extensive observations of a peculiar object, the nearby quasar HE0450-2958 (see ESO PR 23/05 for a previous study of this object), which is the only one for which a host galaxy has not yet been detected [1]. HE0450-2958 is located some 5 billion light-years away.

Until now, it was speculated that the quasar’s host galaxy was hidden behind large amounts of dust, and so the astronomers used a mid-infrared instrument on ESO’s Very Large Telescope for the observations [2]. At such wavelengths, dust clouds shine very brightly, and are readily detected. “Observing at these wavelengths would allow us to trace dust that might hide the host galaxy,” says Knud Jahnke, who led the observations performed at the VLT. “However, we did not find any. Instead we discovered that an apparently unrelated galaxy in the quasar’s immediate neighbourhood is producing stars at a frantic rate.”

These observations have provided a surprising new take on the system. While no trace of stars is revealed around the black hole, its companion galaxy is extremely rich in bright and very young stars. It is forming stars at a rate equivalent to about 350 Suns per year, one hundred times more than rates for typical galaxies in the local Universe.

Earlier observations had shown that the companion galaxy is, in fact, under fire: the quasar is spewing a jet of highly energetic particles towards its companion, accompanied by a stream of fast-moving gas. The injection of matter and energy into the galaxy indicates that the quasar itself might be inducing the formation of stars and thereby creating its own host galaxy; in such a scenario, galaxies would have evolved from clouds of gas hit by the energetic jets emerging from quasars.

“The two objects are bound to merge in the future: the quasar is moving at a speed of only a few tens of thousands of km/h with respect to the companion galaxy and their separation is only about 22 000 light-years,” says Elbaz. “Although the quasar is still ‘naked’, it will eventually be ‘dressed’ when it merges with its star-rich companion. It will then finally reside inside a host galaxy like all other quasars.”

Hence, the team have identified black hole jets as a possible driver of galaxy formation, which may also represent the long-sought missing link to understanding why the mass of black holes is larger in galaxies that contain more stars [3].

“A natural extension of our work is to search for similar objects in other systems,” says Jahnke.

Future instruments, such as the Atacama Large Millimeter/submillimeter Array, the European Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope will be able to search for such objects at even larger distances from us, probing the connection between black holes and the formation of galaxies in the more distant Universe.

Notes

[1] Supermassive black holes are found in the cores of most large galaxies; unlike the inactive and starving one sitting at the centre of the Milky Way, a fraction of them are said to be active, as they eat up enormous amounts of material. These frantic actions produce a copious release of energy across the whole electromagnetic spectrum; particularly spectacular is the case of quasars, where the active core is so overwhelmingly bright that it outshines the luminosity of the host galaxy.

[2] This part of the study is based on observations performed at mid-infrared wavelengths, with the powerful VLT spectrometer and imager for the mid-infrared (VISIR) instrument at the VLT, combined with additional data including: spectra acquired using VLT-FORS, optical and infrared images from the NASA/ESA Hubble Space Telescope, and radio observations from the Australia Telescope National Facility.

[3] Most galaxies in the local Universe contain a supermassive black hole with a mass about 1/700th the mass of the stellar bulge. The origin of this black hole mass versus stellar mass relation is one of the most debated subjects in modern astrophysics.

More Information

This research was presented in papers published in the journal Astronomy & Astrophysics: “Quasar induced galaxy formation: a new paradigm?” by Elbaz et al., and in the Astrophysical Journal “The QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG” by Jahnke et al.

The team is composed of David Elbaz (Service d’Astrophysique, CEA Saclay, France), Knud Jahnke (Max Planck Institute for Astronomy, Heidelberg, Germany), Eric Pantin (Service d’Astrophysique, CEA Saclay, France), Damien Le Borgne (Paris University 6 and CNRS, Institut d'Astrophysique de Paris, France) and Géraldine Letawe (Institut d'Astrophysique et de Géophysique, Université de Liège, Belgium).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Contacts

David Elbaz
CEA, Saclay, France
Phone: +33 (0)1 69 08 54 39
E-mail: delbaz (at) cea.fr

Knud Jahnke
Max Planck Institute for Astronomy, Heidelberg
Phone: +49 6221 528 398
E-mail: jahnke (at) mpia-hd.mpg.de

Cosmic "Dig" Reveals Vestiges of the Milky Way's Building Blocks

GARCHING, GERMANY (Nov. 27, 2009) – Peering through the thick dust clouds of our galaxy’s "bulge" (the myriads of stars surrounding its centre), and revealing an amazing amount of detail, a team of astronomers has unveiled an unusual mix of stars in the stellar grouping known as Terzan 5. Never observed anywhere in the bulge before, this peculiar "cocktail" of stars suggests that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of a proto-galaxy that merged with the Milky Way during its very early days.

FIGURE CAPTION – Peering through the thick dust clouds of our galaxy's central parts (the "bulge") with an amazing amount of detail, a team of astronomers has revealed an unusual mix of stars in the stellar grouping known as Terzan 5. Never observed anywhere in the bulge before, this peculiar cocktail of stars suggests that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of a dwarf galaxy that merged with the Milky Way during its very early days. This near-infrared image was obtained with the Multi-conjugate Adaptive Optics Demonstrator (MAD) instrument on ESO's Very Large Telescope. Observations in two bands (J and K) were combined. The field of view is 40 arcseconds across

“The history of the Milky Way is encoded in its oldest fragments, globular clusters and other systems of stars that have witnessed the entire evolution of our galaxy,” says Francesco Ferraro from the University of Bologna, lead author of a paper appearing in this week’s issue of the journal Nature. “Our study opens a new window on yet another piece of our galactic past.”

Like archaeologists, who dig through the dust piling up on top of the remains of past civilisations and unearth crucial pieces of the history of mankind, astronomers have been gazing through the thick layers of interstellar dust obscuring the bulge of the Milky Way and have unveiled an extraordinary cosmic relic.

The target of the study is the star cluster Terzan 5. The new observations show that this object, unlike all but a few exceptional globular clusters, does not harbour stars which are all born at the same time — what astronomers call a “single population” of stars. Instead, the multitude of glowing stars in Terzan 5 formed in at least two different epochs, the earliest probably some 12 billion years ago and then again 6 billion years ago.

“Only one globular cluster with such a complex history of star formation has been observed in the halo of the Milky Way: Omega Centauri,” says team member Emanuele Dalessandro. “This is the first time we see this in the bulge.”

The galactic bulge is the most inaccessible region of our galaxy for astronomical observations: only infrared light can penetrate the dust clouds and reveal its myriads of stars. “It is only thanks to the outstanding instruments mounted on ESO’s Very Large Telescope,” says co-author Barbara Lanzoni, “that we have finally been able to ‘disperse the fog’ and gain a new perspective on the origin of the galactic bulge itself.”

A technical jewel lies behind the scenes of this discovery, namely the Multi-conjugate Adaptive Optics Demonstrator (MAD), a cutting-edge instrument that allows the VLT to achieve superbly detailed images in the infrared. Adaptive optics is a technique through which astronomers can overcome the blurring that the Earth’s turbulent atmosphere inflicts on astronomical images obtained from ground-based telescopes; MAD is a prototype of even more powerful, next-generation adaptive optics instruments [1].

Through the sharp eye of the VLT, the astronomers also found that Terzan 5 is more massive than previously thought: along with the complex composition and troubled star formation history of the system, this suggests that it might be the surviving remnant of a disrupted proto-galaxy, which merged with the Milky Way during its very early stages and thus contributed to form the galactic bulge.

“This could be the first of a series of further discoveries shedding light on the origin of bulges in galaxies, which is still hotly debated,” concludes Ferraro. “Several similar systems could be hidden behind the bulge’s dust: it is in these objects that the formation history of our Milky Way is written.”

Notes

[1] Telescopes on the ground suffer from a blurring effect introduced by atmospheric turbulence. This turbulence causes the stars to twinkle in a way that delights poets but frustrates astronomers, since it smears out the fine details of the images. However, with adaptive optics (AO) techniques, this major drawback can be overcome so that the telescope produces images that are as sharp as theoretically possible, i.e. approaching conditions in space. Adaptive optics systems work by means of a computer-controlled deformable mirror that counteracts the image distortion introduced by atmospheric turbulence. It is based on real-time optical corrections computed at very high speed (many hundreds of times each second) from image data obtained by a wavefront sensor (a special camera) that monitors light from a reference star, Present AO systems can only correct the effect of atmospheric turbulence in a very small region of the sky — typically 15 arcseconds or less — the correction degrading very quickly when moving away from the reference star. Engineers have therefore developed new techniques to overcome this limitation, one of which is multi-conjugate adaptive optics. MAD uses up to three guide stars instead of one as references to remove the blur caused by atmospheric turbulence over a field of view thirty times larger than existing techniques (ESO PR 19/07).

More Information

This research was presented in a paper that appears in the 26 November 2009 issue of Nature , “The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge”, by F. R. Ferraro et al..

The team is composed of Francesco Ferraro, Emanuele Dalessandro, Alessio Mucciarelli and Barbara Lanzoni (Department of Astronomy, University of Bologna, Italy), Giacomo Beccari (ESA, Space Science Department, Noordwijk, Netherlands), Mike Rich (Department of Physics and Astronomy, UCLA, Los Angeles, USA), Livia Origlia, Michele Bellazzini and Gabriele Cocozza (INAF – Osservatorio Astronomico di Bologna, Italy), Robert T. Rood (Astronomy Department, University of Virginia, Charlottesville, USA), Elena Valenti (ESO and Pontificia Universidad Catolica de Chile, Departamento de Astronomia, Santiago, Chile) and Scott Ransom (National Radio Astronomy Observatory, Charlottesville, USA).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Contacts

Francesco Ferraro
Università di Bologna, Italy
Phone: +39 (0)5 12 09 57 74
E-mail: francesco.ferraro3 (at) unibo.it

An Introduction to Stellar Evolution

Thanks to a new generation of telescopes, the never-ending story of Stellar Evolution is told in spectacular detail. Telescopic ultrasound -- a camera sensitive to infrared light -- monitors prenatal suns incubating inside clouds of hydrogen gas and newborn protostars emitting ultraviolet energy. What happens to stars after they die? From supernova explosions to black holes, the demise of stars eventually leads to new suns, new planets and possibly new life.

Atlas of the Universe

This web page is designed to give everyone an idea of what our universe actually looks like. There are nine main maps on this web page, each one approximately ten times the scale of the previous one. The first map shows the nearest stars and then the other maps slowly expand out until we have reached the scale of the entire visible universe.

Click link below to explore further...

Stellar evolution

Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years (for the most massive) to trillions of years (for the least massive), considerably more than the age of the universe.

Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at the various points in their life, and by simulating stellar structure with computer models.

Early Life

All stars form from clouds of gas and dust condensing in deep space. Only the chemical composition of this cloud, and the amount of material in the cloud that condenses into the actual star, determines what will happen to the star over its entire lifetime.

As an interstellar gas cloud starts to condense under its own gravitation, any tiny amount of spin that it has will become amplified, the way a whirling figure skater spins faster when he brings in his arms. Eventually, little whirlpools or eddies will form in this ever-more-rapidly-spinning collapsing cloud. It's these eddies that will eventually form star systems.

All that gaseous material falling in on itself in a given eddy releases an enourmous amount of heat when it starts to collide with itself. The more the whirlpool contracts, the hotter and more opaque it gets, until it gets hot enough and thick enough to glow. Such an object is called a protostar; we can see such an object from here on Earth, provided the cloud of gas and dust surrounding it is thin enough to see through.

When the protostar is nearly finished collapsing under its own weight, it will reach its maximum temperature. On the surface, it will actually be hotter than it will when it becomes a main-sequence star. But it's the temperature deep within its core that determines the protostar's fate. In most cases, the protostar's total mass will be less than about eight percent the mass of the sun, and the core temperature and pressure will not be high enough for thermonuclear reactions to begin; or, if they are, the initial belch of nuclear activity will push the outer layers of the protostar outward and rarefy the core enough to snuff the fusion reactions out. Such a "failed star" is called a brown dwarf and is probably one of the most plentiful, if hard-to-detect, objects in the galaxy.

Main Sequence Evolution

In some cases, though, the protostar's mass (and therefore its peak core temperature) will be high enough to ignite stable thermonuclear reactions. Soon thereafter, the fusion energy released from the new stellar core reaches its surface, the initial birthing contractions finish, and the newborn star settles down onto the Main Sequence, where it will spend most of its productive lifetime.

Figure showing "Main Sequence": The most famous diagram in astronomy is the Hertzsprung-Russell diagram, which plots the actual brightness (or absolute magnitude) of a star against its color index (represented as B-V). The main sequence is visible as a prominent diagonal band that runs from the upper left to the lower right. This plot shows 22,000 stars from the Hipparcos Catalogue together with 1,000 low-luminosity stars (red and white dwarfs) from the Gliese Catalogue of Nearby Stars (source: Atlas of the Universe).

Since main-sequence stars do not shrink appreciably over time, all of a main-sequence star's radiant energy must be produced in the core by hydrogen fusion. There are two distinct types of hydrogen-burning reactions that stellar core material can undergo. Main-sequence stars lighter than about class F0 fuse hydrogen into helium via the proton-proton chain. This is a rather straightforward nuclear reaction:

two protons fuse together, forming a deuterium nucleus and releasing both a neutrino and a positron (the positron eventually annihilates with an electron to produce energy);
then, another proton collides with the deuterium nucleus, forming a helium-3 nucleus and giving off a gamma ray photon;
finally, another helium-3 nucleus formed by steps 1 and 2 above collides with this helium-3 nucleus, turning it into an ordinary helium-4 nucleus and releasing two protons.

The total reaction time for this entire process is on the order of one million years.

Heavier main-sequence stars take advantage of their higher core temperatures to fuse hydrogen into helium more rapidly, by a process called the CNO cycle. This is a six-step process which uses ordinary carbon-12 as a kind of nuclear catalyst. The net result is the same: four protons turn into a helium-4 nucleus and two positrons, liberating energy in the process, while all the other materials that partook in the reaction come out unchanged. (Note that, as carbon is required for this reaction, galactic halo population stars will be too heavy-element-poor to undergo it on a large scale; heavy main-sequence stars in the galactic halo use the proton-proton chain just like lighter stars do.) Unlike the slow proton-proton chain, a CNO cycle reaction is about a thousand times faster, taking only a thousand or so years to complete. This means that heavier main-sequence stars that are heavy-element-rich will shine much more brightly than lighter main-sequence stars. It also means that the heavier stars will burn out their core's supply of nuclear fuel much faster.

How hot, and large, and long-lived will a star be once it enters the main sequence? That all depends on its mass:

Avg. Mass	    spectral class	Avg. Luminosity	Avg. Diameter	Main sequence lifetime
40 x Sol		O5	500 000 x Sol	18 x Sol		1 million years
17 x Sol		B0	20 000 x Sol	7.6 x Sol		10 million years
7 x Sol		B5	800 x Sol		4.0 x Sol		100 million years
3.6 x Sol		A0	80 x Sol		2.6 x Sol		500 million years
2.2 x Sol		A5	20 x Sol		1.8 x Sol		1000 million years
1.8 x Sol		F0	6 x Sol		1.3 x Sol		2000 million years
1.4 x Sol		F5	2.5 x Sol		1.2 x Sol		4000 million years
1.1 x Sol		G0	1.3 x Sol		1.04 x Sol		10 000 million years
1.0 x Sol		G2 (sun)	1.0 x Sol		1.00 x Sol		12 000 million years
0.9 x Sol		G5	0.8 x Sol		0.93 x Sol		15 000 million years
0.8 x Sol		K0	0.4 x Sol		0.85 x Sol		20 000 million years
0.7 x Sol		K5	0.2 x Sol		0.74 x Sol		30 000 million years
0.5 x Sol		M0	0.03 x Sol		0.63 x Sol		75 000 million years
0.2 x Sol		M5	0.008 x Sol	0.32 x Sol		200 000 million years

(Note that the luminosities and estimated main-sequence lifetime for stars hotter than spectral class F0 assumes it is heavy-element-rich enough to have sufficient carbon to run the CNO cycle; a heavy-element-poor star hotter than F0 would be considerably dimmer and last considerably longer. It should also be noted that the currently estimated age of the universe, according to big bang theory, is between 10 000 and 20 000 million years -- shorter than the lifespan of a class K or M main-sequence star. This means it should be impossible to find the remnants of any former K or M main-sequence stars anywhere in the known universe. If we ever find any, our picture of the universe -- or of stellar evolution -- will have to be revised.)

End of Life

And what happens to a star when it's reached the end of its main sequence lifetime, when it's exhausted about half the available fuel in its core and can no longer sustain a hydrogen fusion reaction at the rate it once did? Well, like its properties during its main sequence lifetime, that all depends on the mass of the star.

Lightweight Stars

Stars whose main sequence spectral class was anywhere from M on up through the A's will start the Beginning of the End by slowly expanding into a Red Giant (a spectral class M or K star with a luminosity class of III). When nuclear fuel is no longer plentiful in the core, it can no longer maintain its main-sequence outward pressure and begins to contract under its own weight. As it collapses, the layers above it fall inward on top of it, causing them to heat up. Soon, the layer immediately above the core will become hot enough and high-pressure enough to undergo thermonuclear reactions on its own -- and since this layer has an ample supply of hydrogen (unlike the exhausted core), it becomes a self-sustaining hydrogen-burning shell and will actually burn hydrogen into helium faster than the core did during its main-sequence lifetime. The added energy and outward pressure from this hydrogen-burning shell stops the collapse of the upper layers; in fact they begin expanding, and will keep expanding until the star becomes a Red Giant. It takes thousands of years for a star to grow from initial-collapse-at-the-end-of-the-main-sequence to the full-blown red giant stage (a 1962 study claims that it takes "only" about 20 000 years for a spectral class A main-sequence star to evolve into a class M red giant).

After a few million years, the new hydrogen-burning shell will exhaust itself also. This causes the star to contract under its own weight once again. Briefly, the super-compacted core may flash into life, fusing helium into carbon for a brief instant measured literally in seconds (the reaction rate for helium fusion is about a million million times faster than hydrogen fusion), but as helium-fusion produces much less energy than hydrogen-fusion does, and since the core is buried so deeply within the star, this helium flash will not be seen and is only predicted in theory. Finally, as this last burp of energy generated by the helium flash slowly reaches the surface, the star becomes a red giant a second time, sheds up to half its mass into interstellar space as a so-called "planetary nebula," and leaves only its core behind.

The core that it leaves behind, though, is a fascinating object. It weighs about half of what the star did during its main sequence lifetime, yet it's smaller than Uranus or Neptune. It's hotter than the star was when it was on the main sequence, and gives off blackbody radiation just like a hot star would; yet it produces no energy of its own and glows simply because it hasn't cooled off yet. Its surface gravity can measure well over 100 000 times the surface gravity of the Earth. Its average density is over a ton to the cubic centimeter; it is so incredibly dense, in fact, that all the atoms that make it up are packed together as tightly as the laws of Fermion physics will allow, making it a totally incompressible "electron degenerate" gas. This oddball super-dense stellar remnant is called a white dwarf.

Electron-degeneracy theory predicts that the uppermost mass a white dwarf can attain is about 1.4 times the mass of the sun, called the Chandrasekhar Limit. Any heavier, and the tremendous pressure on the innermost atoms would squeeze their electrons into the nuclei they orbit, turning all the protons and electrons in the star into neutrons. So far, no white dwarfs of more than 1.4 solar masses have been found, so the theory seems to be on firm ground.

The low surface area and high specific heat of a white dwarf means that such an object would take a long time to cool off -- longer, even, than the currently estimated age of the universe. If the universe were a few hundred thousand million years older, we would expect it to be populated by white dwarfs that have cooled off below the point where they glow; these academic objects are referred to as black dwarfs.

Middleweight Stars

A class B main-sequence star will leave the main sequence much as lighter stars do, collapsing a little, forming a hydrogen-burning shell, turning into a Red Giant (or a Cepheid variable like Polaris), shrinking again as its hydrogen-burning shell exhausts itself, then shining more brightly as its core goes through a helium-burning phase. The difference now, though, is that burning helium into carbon in the star's core is no longer the end of the road. As this fuel supply runs out, the star's collapse reignites the depleted hydrogen-burning shell and turns it into a helium-burning shell. This renewed energy then creates a new hydrogen burning shell in a layer above the old one, so that as we move inward from the star's surface, we get a hydrogen burning shell, then a helium burning shell, and finally the core underneath. The core will likewise undergo renewed thermonuclear vigor, fusing its old carbon together with more helium to form oxygen.

When this stage completes, the core can begin fusing oxygen into neon, the old helium-burning shell can become a carbon-burning shell, the formerly outermost hydrogen-burning shell becomes the new helium-burning shell, and yet another thin hydrogen-burning shell emerges outside of that. And then, neon can fuse into magnesium, then magnesium can fuse into silicon, and so on down the periodic chart until, finally, chromium gets fused into iron. Each of these fusion stages (helium-to-carbon, carbon-to-oxygen, . . . , chromium-to-iron) produces less energy than the preceding stage does, and thus exhausts its own fuel supply ever more rapidly. During these late stages of its evolution, the star can bloat up to hundreds of times the diameter of the sun, becoming a red supergiant like Betelgeuse.

Finally, though, when the star gets around to wanting to fuse iron into something heavier, it runs into a problem. Iron is at the "bottom of the well" when it comes to nuclear reactions. Fusing it into something heavier, or for that matter breaking it apart into something lighter, always consumes more energy than it produces. So when the core starts to "burn" iron, it ends up getting cooler, not hotter. All the outward pressure that its nuclear reactions have been generating suddenly vanishes. The star's core collapses in the blink of an eye. And, since the core takes up such a large fraction of the star's total mass, it's heavier than the maximum 1.4 solar masses that can support a white dwarf. Its protons and electrons get squeezed together until it is a solid ball of neutrons, no bigger across than Los Angeles and with the density of an atomic nucleus (around a thousand million tons to the cubic centimeter). It is now a neutron star and is said to be "neutron-degenerate." The surface gravity of such a beast is on the order of a million million G's.

In collapsing in on itself to such dense proportions, all of the core's gravitational potential energy has to be released in the form of heat, just like the collapsing cloud that originally formed the star heated up as it contracted. This time, though, the amount of energy released is much greater and happens over the span of a few seconds. All the outer layers of the star, even those that never became nuclear fusion shells, will become superheated plasmas hot enough to fuse their constituent ions into not only iron, but copper, strontium, silver, gold, lead -- even uranium. These super-hot, super-bright outer layers race off into interstellar space at nearly the speed of light, carrying their newly-formed heavy elements with them and creating one of the most spectacular and rare sights in the heavens: a type II supernova.

(Incidentally, it's believed that supernovae are the only phenomena that can send heavy elements into the interstellar medium. Thus, the heavy element enrichment that our solar system enjoys is thought to be the product of earlier supernovas that infused their products into the cloud that our own sun (and its planets) condensed out of.)

With the aid of telescopes, the expanding cloud from a type II supernova can be seen for many centuries hence as a nebula (such as the crab nebula). The neutron star left at the cloud's center is too small to be seen with current instruments, but it can be detected by its radio emissions if one of its magnetic poles happens to sweep past the Earth as the star rotates. (Its collapse to such a compact object means it will be spinning very rapidly; its magnetic pole may sweep past the Earth hundreds of times a second. It would thus appear to a radio telescope to be a very rapidly, regularly pulsating radio source called a pulsar.)

Heavyweight Stars

The rare class O main-sequence stars start the end of their lives as the middleweight stars do, bloating, forming energy-producing shells around the core, and fusing heavier and heavier elements together until the core becomes iron. And, once again, when the core attempts to fuse iron into something heavier, it loses its energy support and collapses, crossing the Chandrasekhar Limit and squeezing itself into a ball of neutrons.

There is, however, a theoretical limit on how heavy even a neutron star can become. Past about three solar masses, even neutron degeneracy can't support the core's weight. In fact, no force known can support its weight. The core continues to collapse until it is an infinitely small, infinitely dense point called a singularity. Its gravity will be so strong that neither the material from the original core's outer layers, nor the energy from the core's collapse, nor even a beam of light directed straight outward can escape it. Nothing that comes within the Schwarzchild Radius (3 kilometers times the mass of the singularity in solar masses) can escape it. As far as the outer layers of the star are concerned, the core has merely fizzled out, removing its energy support and letting them fall; these outer layers too will fall within the singularity's gravitational grip never to be seen again. The whole star swallows itself, leaving only its gravity behind; it's now called a black hole.

A word about novae and X-ray bursters

In a binary star system, one star will usually be more massive than the other, meaning that the heavier star of the pair may end its main-sequence lifetime millions or thousands of millions of years before its lighter companion does. Many white dwarfs, for instance, have been detected because of oddities in the movement or appearance of their main-sequence companion -- Sirius B being the most famous example, discovered by accident over a century ago when a new telescope lens resolved Sirius's companion during a test. Sometimes, due to orbital decay or the fact that the longer-lived companion star has reached the end of its lifetime and is turning into a red giant, a white dwarf , neutron star, or black hole can come so close to its binary host-star that its strong gravity begins drawing (or "accreting") material off its host. Such a system is called a mass-exchange binary.

This sucked-up gas swirls around the white dwarf or neutron star, forming an accretion disk as it siprals in toward its new owner's surface. In the case of a neutron star or black hole, the accretion disk will be the only feature of the companion star visible from the Earth. Material accreted "onto" a black hole essentially goes down the event-horizon drain and is gone forever. Material accreted onto a neutron star or white dwarf, however, will accumulate on that star's surface, forming thicker and thicker layers of super-compressed hydrogen. If the infalling material is moving fast enough, this accreted hydrogen can gain sufficient heat and pressure for thermonuclear reactions to occur.

Depending on how fast the incoming material is moving, several things can happen to a white dwarf. Very rapidly infalling material will ignite all at once, causing the white dwarf to shine several times more brightly than its companion for a few days, then taper off back down to its original brightness. Years or centuries later, the process may repeat itself. This phenomenon is called a nova (the Latin word for "new") because, to the unaided eye, it looks like a new star has appeared in the sky where before there was none. If the accreted material is trickling in more slowly, it will only ignite in small spurts, turning the white dwarf into a cataclysmic variable. If the accreted material accumulates very slowly, the white dwarf can heat up as a whole, until the entire star blows itself apart in one massive thermonuclear fireball called a type I supernova.

A neutron star whose accreted layers ignite will burn all its available newfound hydrogen into helium in a matter of seconds. This is only visible as an intense burst of X-rays lasting for, at most, a minute or two. The process repeats itself sporadically every few hours as new material is accreted. Not surprisingly, such phenomena are called X-ray bursters.

Interactive Tour: Stellar Evolution

The Milky Way galaxy contains several hundred billion stars of various ages, sizes and masses. A star forms when a dense cloud of gas collapses until nuclear reactions begin deep in the interior of the cloud and provide enough energy to halt the collapse.

Many factors influence the rate of evolution, the evolutionary path and the nature of the final remnant. By far the most important of these is the initial mass of the star. This interactive piece illustrates in a general way how stars of different masses evolve and whether the final remnant will be a white dwarf, neutron star, or black hole.

Click link below for an intereactive tour on Stellar Evolution... (also available in pdf form)

Carl Sagan "Pale Blue Dot"

From the source:

From the Carl Sagan's Pale Blue Dot. There are several different versions of "The Pale Blue Dot" on-line. The actual words were taken from Carl Sagan's "Pale Blue Dot" audio-book, the music was performed by Vangelis but was extracted from the Cosmos DVD (English audio track 2 has no narration, just the background sounds and the music.) All the pictures inserted into the video portray what I feel Carl Sagan was trying to say.

If you can afford to purchase the Cosmos television series, please do so and support those who made it available so that they can continue to make it available to those of this generation and those who will come in later generations. Buy it at http://www.carlsagan.com or from any major DVD retailer. If you cannot afford to buy the DVD set, and would still like to educate yourself, it is available for free rental at most public libraries. Thank you for your interest.

First Black Holes May Have Incubated in Giant, Starlike Cocoons

BOULDER, CO (Nov. 23, 2009) – The first large black holes in the universe likely formed and grew deep inside gigantic, starlike cocoons that smothered their powerful x-ray radiation and prevented surrounding gases from being blown away, says a new study led by the University of Colorado at Boulder.

The formation process involved two stages, said Mitchell Begelman, a professor and the chair of CU-Boulder's astrophysical and planetary sciences department. The predecessors to black hole formation, objects called supermassive stars, probably started forming within the first few hundred million years after the Big Bang some 14 billion years ago. A supermassive star eventually would have grown to a huge size -- as much as tens of millions of times the mass of our sun -- and would have been short-lived, with its core collapsing in just in few million years, he said.

In the new study to be published in Monthly Notices of the Royal Astronomical Society in London, Begelman calculated how supermassive stars might have formed, as well as the masses of their cores. These calculations allowed him to estimate their subsequent size and evolution, including how they ultimately left behind "seed" black holes.

Begelman said the hydrogen-burning supermassive stars would had to have been stabilized by their own rotation or some other form of energy like magnetic fields or turbulence in order to facilitate the speedy growth of black holes at their centers. "What's new here is we think we have found a new mechanism to form these giant supermassive stars, which gives us a new way of understanding how big black holes may have formed relatively fast," said Begelman.

The main requirement for the formation of supermassive stars is the accumulation of matter at a rate of about one solar mass per year, said Begelman. Because of the tremendous amount of matter consumed by supermassive stars, subsequent seed black holes that formed in their centers may have started out much bigger than ordinary black holes -- which are the mass of only a few Earth suns -- and subsequently grew much faster.

After the seed black holes formed, the process entered its second stage, which Begelman has dubbed the "quasistar" stage. In this phase, black holes grew rapidly by swallowing matter from the bloated envelope of gas surrounding them, which eventually inflated to a size as large as Earth's solar system and cooled at the same time, he said.

Once quasistars cooled past a certain point, radiation began escaping at such a high rate that it caused the gas envelope to disperse and left behind black holes up to 10,000 times or more the mass of Earth's sun, Begelman said. With such a big head start over ordinary black holes, they could have grown into supermassive black holes millions or billions of times the mass of the sun either by gobbling up gas from surrounding galaxies or merging with other black holes in extremely violent galactic collisions.

The quasistar phase was analyzed in a 2008 paper published by Begelman in collaboration with CU Professor Phil Armitage and Research Associate Elena Rossi.

"Until recently, the thinking by many has been that supermassive black holes got their start from the merging of numerous, small black holes in the universe," he said. "This new model of black hole development indicates a possible alternate route to their formation."

Black holes are extremely dense celestial objects believed to be formed by the collapse of stars and which have such a strong gravitational field that nothing, not even light, can escape. While black holes are not directly detectable by astronomers, the movement of stellar matter swirling around them and powerful jets of gas blasting outward provides evidence for their existence. Ordinary black holes are thought to be remnants of stars slightly larger than our sun that used up their fuel and died, he said.

The supermassive black holes created early in the history of the universe may have gone on to produce the phenomenon of quasars -- the very bright, energetic centers of distant galaxies that can be a trillion times brighter than our sun. There also is evidence that a supermassive black hole inhabits the center of every massive galaxy today, including our own Milky Way, said Begelman.

"Big black holes formed via these supermassive stars could have had a huge impact on the evolution of the universe, including galaxy formation," he said. Begelman is collaborating with University of Michigan astrophysicist Marta Volonteri, comparing the possible formation of supermassive black holes from supermassive stars and quasistars versus their creation by the merging of ordinary black holes left behind by the collapse of the universe's earliest stars.

Scientists may be able to use NASA's James Webb Space Telescope, slated for launch in 2013, to look back in time and hunt for the cocoon-like supermassive stars near the edges of the early universe, which would shine brightly in the near infrared portion of the electromagnetic spectrum, said Begelman.

Begelman has authored several books, including "Gravity's Fatal Attraction" with Martin Rees, a member of the British House of Lords and president of the Royal Society of London and who is the British Astronomer Royal, in 1996. The second edition of the book is due out early next year. Begelman also authored "Turn Right at Orion: Travels Through the Cosmos" in 2000.

-CU-

Contact

Mitchell Begelman, 303-492-7856
Mitchell.begelman@colorado.edu
Jim Scott, 303-492-3114
Jim.scott@colorado.edu

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Mars News

News about Mars from Science Daily

Baffling Galactic Bulge

GARCHING, GERMANY (Nov. 18, 2009) – Just as many people are surprised to find themselves packing on unexplained weight around the middle, astronomers find the evolution of bulges in the centres of spiral galaxies puzzling. A recent NASA/ESA Hubble Space Telescope image of NGC 4710 is part of a survey that astronomers have conducted to learn more about the formation of bulges, which are a substantial component of most spiral galaxies.

When targeting spiral galaxy bulges, astronomers often seek edge-on galaxies, as their bulges are more easily distinguishable from the disc. This exceptionally detailed edge-on view of NGC 4710 taken by the Advanced Camera for Surveys (ACS) aboard Hubble reveals the galaxy's bulge in the brightly coloured centre. The luminous, elongated white plane that runs through the bulge is the galaxy disc. The disc and bulge are surrounded by eerie-looking dust lanes.

When staring directly at the centre of the galaxy, one can detect a faint, ethereal "X"-shaped structure. Such a feature, which astronomers call a "boxy" or "peanut-shaped" bulge, is due to the vertical motions of the stars in the galaxy's bar and is only evident when the galaxy is seen edge-on. This curiously shaped puff is often observed in spiral galaxies with small bulges and open arms, but is less common in spirals with arms tightly wrapped around a more prominent bulge, such as NGC 4710.

NGC 4710 is a member of the giant Virgo Cluster of galaxies and lies in the northern constellation of Coma Berenices (the Hair of Queen Berenice). It is not one of the brightest members of the cluster, but can easily be seen as a dim elongated smudge on a dark night with a medium-sized amateur telescope. In the 1780s, William Herschel discovered the galaxy and noted it simply as a "faint nebula". It lies about 60 million light-years from the Earth and is an example of a lenticular or S0-type galaxy – a type that seems to have some characteristics of both spiral and elliptical galaxies.

Astronomers are scrutinising these systems to determine how many globular clusters they host. Globular clusters are thought to represent an indication of the processes that can build bulges. Two quite different processes are believed to be at play regarding the formation of bulges in spiral galaxies: either they formed rather rapidly in the early Universe, before the spiral disc and arms formed; or they built up from material accumulating from the disc during a slow and long evolution. In this case of NGC 4710, researchers have spotted very few globular clusters associated with the bulge, indicating that its assembly mainly involved relatively slow processes.

Notes for editors:

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image credit: NASA & ESA

These observations were obtained by a team led by Paul Goudfrooij from the Space Telescope Science Institute in Baltimore, Maryland, USA.

Contacts:

Colleen Sharkey
Hubble/ESA, Garching, Germany
Tel: +49 89 3200 6306
Cell: +49 151 153 73591
E-mail: csharkey@eso.org

Radio Galaxies: Early Universe

Radio galaxies are cosmic beacons, with the brightest ones beaming nearly a trillion solar-luminosities of radiation into space at radio wavelengths. The origin of this intense emission is the environment of the massive black hole at the galaxy's nucleus -- a so-called active galactic nucleus (AGN). It is thought that electrons moving rapidly in strong magnetic fields produce the radio emission, but at the same time high temperature regions near the AGN also radiate intensely at other wavelengths. Astronomers are interested in understanding the physics underway in these extreme cosmic radio sources, and whether they are cosmic oddities or a normal evolutionary stage of galaxies like our own Milky Way.

SAO astronomers Giovanni Fazio and Steve Willner, along with nine of their colleagues, used the Spitzer Space Telescope to study two well known radio galaxies whose light has been traveling for over eleven billion years -- more than 80% of the lifetime of the universe. Formed when the universe was still relatively young, these objects demonstrate that whatever physical processes are at work in radio galaxies, they also were effective in the early universe. Vigorous star formation in local galaxies, for example, is usually accompanied by emission from small, carbon-rich grains called polyaromatic hydrocarbons, or PAHs. The scientists report finding the first evidence for PAHs in distant radio galaxies, a clear indication that in addition to their luminous AGN, these ancestral galaxies also are busy making new stars. The results help to show that these early radio galaxies look quite similar to modern ones despite the youth of the cosmos. Because they are particularly bright (and hence detectable by us), their presence also suggests that there may be many more, less dramatic but nonetheless still active, radio galaxies contributing to this early epoch of cosmic development.

Sun: Magnetic Fields

Solar flares, prominences, and so-called coronal mass ejections are three different manifestations of stored magnetic energy near the sun's surface being released in sudden eruptions. The energy for these dramatic events comes ultimately from the motions of the charged particles in the hot gas. There is considerable interest in understanding these events because of their potentially disruptive effects on earth via the solar wind.

In the traditional explanation, called the "storage model," the stressed magnetic field is suddenly realigned, something like a rubber band snapping, but remains in tact. The problem with this explanation is that it predicts that the magnetic field strength following eruptive events should (to a substantial degree) remain unchanged, while a recent series of observations implies a much more complex picture with magnetic field changes that have seriously challenged the storage model. SAO astronomer Jun Lin and his student have published a new paper showing that these objections can be resolved with a more sophisticated understanding of the processes at work in the sun. They calculate that previously uncorrected line-of-sight effects can seriously distort the observations and must be removed, and that key processes originate from a series of layers in the solar surface, not a single shell. Together, these and some other effects can successfully explain the observations in the context of the storage model. The work strengthens the case for the storage model, but the understanding of solar magnetic eruptions is still a work in progress.

Seven Billion Year-old Galaxies

As modern telescopes peer more and more deeply into the universe, they are seeing older and older galaxies. The current record is a galaxy whose light has been traveling towards us for well over 12.5 billion years, 90% of the age of the universe. Astronomers are hard at work trying to understand what these objects are like, both because they are ancestors of our own Milky Way galaxy, and because they form from the seeds sown in the primordial big bang period and so offer clues into those primitive epochs.

Astronomical models use the observations of faint, distant galaxies to look for self-consistency and to refine the models' parameters. One of the key properties of galaxies is clustering -- the way in which hundreds or even thousands of galaxies can be bound together by their mutual gravitational attractions. Clustering not only influences how a particular member galaxy evolves, it also reflects the larger cosmic structures from which all the members form. The task of deciphering clustering in the early universe is difficult to do because distant galaxies are faint and only the brightest ones can be seen. This leaves one of the most crucial parameters of a cluster -- its total mass -- very uncertain indeed.

SAO astronomers Mark Birkinshaw and B. Maughan together, with eight colleagues, have used the Chandra X-ray Observatory and another X-ray satellite, XMM-Newton, to study in unprecedented depth a galaxy cluster that is about seven billion years old, far enough away to probe the cosmological nature of galaxy evolution yet close enough to be measurable. The very hot gas in the cluster emits at X-ray energies, and provides a measure of the total cluster mass because it traces the entire system of galaxies. In this case, the team finds that the total mass of the cluster is equivalent to about 5000 Milky Ways. The main significance of the research, however, is that it confirms for the first time the accuracy of simple models that predict how galaxy clusters evolve from the earliest times, at least for clusters out to a distance of about seven billion light years.

Supermassive Black Hole at Center of Milky Wa

There is now overwhelming evidence that the center of our Milky Way galaxy contains a giant black hole with a mass of about four million suns. The most convincing data come from the motions of stars near the object. Their orbits, traced over sixteen years of observations, show them looping around an unseen mass of this size. Moreover, the data imply that the huge mass is concentrated into less than only 100 AU (one AU - astronomical unit - is the average distance of the earth from the sun). Finally, the stars are observed moving faster than 5000 km/s while an extremely bright radio source associated with the unseen mass appears motionless at the 1 km/s level or less, implying that it must contain much more mass than the stars swinging around it.

Recent measurements of the size of the radio source make it smaller than one AU. Combining the mass and radius of the radio source yields an incredibly high density that can only be achieved by a black hole. The formation and development of our galaxy was enormously influenced by this supermassive black hole (SMBH), and astronomers are therefore trying to understand as many of its properties as they can. It is, furthermore, also by far the closest such dramatic object to us, making it much easier to study than than its cousins at the centers of distant galaxies.

Astronomers think that a disk of very hot material surrounds most SMBHs, and that the disk is likely to have a hot spot (or spots) that rotates around the black hole. A team of CfA astronomers, Mark Reid, Avery Broderick, and Avi Loeb, along with two colleagues, used ultra-precise radio astronomy techniques to try to trace the motions of any hot spot via the apparent location of its radio emission over a few hours, the time it might take for such a spot to move enough to be detected. The measurement is extremely difficult because the radiation is faint yet the observation must be relatively brief (less than an hour), and because the hot disk is expected to have other processes that can confuse the result. Despite the difficulties, the team succeeded in setting a limit of less than about 0.6 AU for any motion of a hot spot - a remarkable precision that comes close to testing some of the fundamental relativistic theories of SMBH behavior. Further research, probably at millimeter or submillimeter rather than radio wavelengths, can extend this result into the regime where models predict hot spots should be detected on these short timescales.

First Stars

New stars are continually forming in clouds of gas and dust in our galaxy. Astronomers at the CfA and elsewhere who watch these births have a very good (though not perfect) understanding of how and why they happen. The natal regions, however, are all rich in elements like carbon and oxygen whose properties facilitate the birth process. These elements, however, did not exist in the early universe - only hydrogen and helium (and a trace of some others) were made in the big bang processes of creation. All the other elements in our world were fabricated in the fusion furnaces of stars, and later ejected into space in supernovae or winds. How, then, did the very first generation of stars in the cosmos come to be without this facilitating material? Answering this fundamental question has long been a goal of astronomy, yet the first stars -- however they came to be -- must have existed so long ago and be so far away that observing any individual ones is out of the question for today's technology.

Theoretical models of the first stars, however, designed using complex computer simulations, have made considerable progress in answering the question. They show that because the first stars could contain only hydrogen and helium, they must have been much more massive than our sun, perhaps one hundred or more times bigger, in order for gravitational collapse to lead to nuclear ignition.

CfA astronomer Lars Hernquist, together with two of his colleagues, has published a new paper in last week's journal of Science that carries these simulations to new levels of precision. Starting with basic cosmological information about the distribution of matter after the big bang, the new computations track the evolution of the primordial clumps of material on spatial scales from hundreds of thousands of light-years down to a small fraction of a stellar radius, a remarkable dynamic range of about ten trillion, and the first time computations have been so detailed. The computations also follow the steadily increasing density of the material, and do so over an even broader range, a factor of nearly a billion trillion, from its state in the diffuse gas until stellar ignition is imminent.

The team's results show that the earliest onset of stellar behavior can occur even when these protostars are much less massive than our sun (as little as 1% of a solar mass). These objects can then act as seeds onto which additional material accretes to create more mature, and much more massive stars. Apparently these small protostars can form in part because disk-like structures develop that allow such small masses to emerge, in contrast to purely spherical collapse that results in much larger protostars. The results are an important advance in our understanding of the nature of the very first stars and how they develop from the minute density ripples left a few hundred million years after the big bang.

Hubble Expansion

Perhaps the most astonishing and revolutionary discovery in cosmology was Edwin Hubble's observation that galaxies are moving away from us. It provides the underpinning of the big bang picture of creation in which the universe is expanding, and has been for 13.7 billion years. But astronomers in the last century were quick to point out to Hubble, and to the theoreticians like Einstein and Lemaitre who modeled his data, that the observations really only find that galaxies appear red. While relativity does predict that galaxies in an expanding universe will appear red, other causes of redness might be at work -- for example, a radical idea called "tired light" in which light in a static universe just grows redder as it travels over cosmic distances towards us.

For over sixty years scientists have tried to determine whether tired light, or perhaps some other effect, might be responsible for the redness of galaxies rather than expansion. One method they used was to watch supernovae. If motion of the object (that is, expansion) is responsible for red galaxies, then these fast moving objects will manifest other effects of their relativistic speeds. Not only the frequency of their light but also the frequency of all their phenomenon will appear to us to be "red," that is, to be happening more slowly. Supernovae, for example, will appear to glow for longer times in galaxies with larger redshifts. And indeed, all of the early studies found that supernovae behaved consistently with this notion, and the idea of tired light gradually lost favor.

Supernova measurements are difficult, however, and subject to numerous uncertainties. For example, the brightest supernovae -- those seen at the farthest distances -- might naturally glow for longer times as a consequence of their extreme luminosities. Indeed, researchers have found that this and other effects do influence supernovae lifetimes, meaning that not all supernovae are exactly identical with each other. CfA astronomers Stephane Blondin, Michael Wood-Vasey, Peter Challis, Bob Kirshner, and Chris Stubbs, along with 27 of their colleagues, have now completed a definitive study that addresses all of these issues and unambiguously excludes the tired-light hypothesis. They watched changes in the spectra of thirteen supernovae in very red galaxies as these supernovae faded away. The time-varying spectral details of the supernovae enabled the team to calibrate the intrinsic ages and luminosities of the supernovae, and provided an accurate measure of the age of the supernovae. The scientists find that red galaxies have supernovae whose timing does indeed appear to be slow, consistent with relativity and the rapid motion of the host galaxies. Their result, which unambiguously rules out the tired-light hypothesis, is the most direct confirmation of the reality of relativistic expansion that has ever been made.

Black Hole Confirmed

In 1967, an X-ray sounding rocket discovered a fantastically bright source of X-ray emission coming from the direction of the constellation of Cygnus. Named Cyg X-3, it was soon identified as coincident with a variable source known to be bright as well at radio wavelengths. Astronomers have since been able to conclude that this object is really a binary star (that is, two objects orbiting around each other) in our galaxy, that it lies about 25,000 light-years away, and that one of the objects is a hot, massive star (soon to become a supernova) with strong winds. But what is the companion object, and why does it cause the pair to emit such intense X-ray emission? Astronomers have been trying to solve this question ever since.

There are two likely possibilities. The first is that the companion is a neutron star - the ultra-dense ash left behind after a supernova explosion. The second possibility is that the companion was originally so massive - more than about eight solar-masses - that its supernova explosion left behind a black hole. As material blowing from the hot star encounters the region around either dense companion, it will be heated to millions of degrees and emit X-rays.

SAO astronomer Michale McCollugh, together with two colleagues, has published an analysis of archival multi-wavelength data of Cyg X-3. Their analysis tries, for the first time, to account for the full behavior of the time-varying source -- its strong, weak, and intermediate phases of flaring emission, as well as the time-varying spectral character of the radiation. When the team compared its results with models and observations of known black hole and neutron binaries, they found that the Cyg-X-3 emission closely corresponds with that seem in black hole systems, both at X-ray and radio wavelengths, and that it differs from the emission seen in neutron star binaries. Although some additional analysis remains to be done, the results appear to have resolved at last one of the important lingering mysteries from the early days of X-ray astronomy.

Super Massive Black Hole at Center of Milky Way

Black holes are by far the "simplest" objects in the universe because they can be completely characterized by just three numbers: their mass, electric charge, and spin. Although they are simple - or perhaps because of it - they are remarkably mysterious, in part because they are impossible to see directly. They are irresistible sinks for matter and energy, surrounded by a zone (the "event horizon") within which anything that ventures will inevitably fall and disappear, even light. Despite their reputation for being pitiless devourers of matter and radiation, however, the environments of black holes are often sources of powerful radiation. Infalling matter can form a disk of material around the event horizon, and when these disks become hot from friction, they radiate copiously. Astronomers are trying to understand black holes because they are fundamental to our understanding of gravity, because they usually form in the final stages of a massive star's life, and because they are thought to be relatively common objects in the universe. Not least, very massive black holes are thought to reside at the centers of most galaxies, and to play a key role in the development of such galaxies.

The center of our Milky Way galaxy, about twenty-five thousand light-years from earth, harbors a four million solar-mass black hole whose environment emits very intense radiation. The event horizon of this black hole is calculated to be one-tenth of an astronomical unit in size, or four times smaller than the distance of the planet Mercury's orbit from the sun. If the bright radiation arises from near this event horizon, then effects of the powerful gravitational fields (so-called gravitational lensing) will make it appear to us as if it were coming from a larger region, about the size of Mercury's orbit.

A team of three SAO astronomers, Jonathan Weintroub, Jim Moran, and Ken Young, together with a team of twenty-five of their colleagues, has pioneered powerful (and very challenging) new technologies that coordinated the Submillimeter Array's (SMA) developments with other submillimeter and millimeter telescopes located in Hawaii, Arizona, and California to enable these telescopes to work together. By doing so, they were able to achieve dramatically improved resolution of the spatial images of the galactic center's black hole region. In fact, the new techniques enabled the system to image sizes as small as the expected, Mercury-orbit-sized event horizon (presuming it radiates with sufficient intensity at the millimeter wavelengths used in the observations).

Writing in last week's issue of Nature, the team reports that the measurements indicate that the radiation is coming from a region smaller than the putative event horizon, by about 30%. But that should be impossible, according to our current understanding, if it really does come from the edge of the event horizon. The implication is that for some as yet unknown reason the brightest portion of the radiation must instead be coming from somewhere else nearby. The team speculated that it could be arising in the flow of material that is accreting onto the disk. The results demonstrate the power of the new interferometric technology, open a new window on the mysterious environment of black holes, and mark the start of a new era probing even finer scale structures around these simplest of cosmic objects.

Galaxies in the Early Universe

About ten years ago, astronomers using new submillimeter wavelength facilities discovered the existence of a new class of very distant galaxies. These objects are located so far away that their light has been traveling towards us for over ten billion years - more than 70% of the lifetime of the universe. Although today they are old, we see them as they were only a few billion years after they formed, when they were relatively young.

These galaxies were undetected in the visible but emit strongly at submillimeter wavelengths because they have an abundance of warm dust. What heats the dust is still controversial - probably either massive star formation, or an active black hole at the galactic nucleus, or perhaps both. Our Milky Way galaxy, or at least the region where the sun resides, probably formed between seven and ten billion years ago, and so understanding these remote systems can also help us understand our own origins.

Fortunately, the Infrared Array Camera on the Spitzer Space Telescope (IRAC; SAO astronomer Giovanni Fazio is the PI of the IRAC team) is sensitive enough to have detected these submillimeter galaxies in the infrared. The IRAC images have led to a breakthrough because of IRAC's spatial precision, which is much higher than that of the submillimeter instruments. Since numerous distant galaxies can appear crowded together in the sky, IRAC's resolution enables scientists to identify which galaxies are the unique submillimeter ones by measuring their infrared emission and infrared color - the submillimeter galaxies are very red. But astronomers still have not been able to figure out what heats the dust. Conventional wisdom holds that the infrared colors are unable to sort out whether star formation or black hole activity dominates the heating.

Three SAO astronomers, Matt Ashby, Giovanni Fazio, and their student Josh Younger, and a team of eleven other scientists, have analyzed a set of forty-seven relatively well studied submillimeter galaxies and compared them to a larger sample of other kinds of galaxies. All forty-seven were detected by IRAC with a signal high enough to determine their colors. By comparing the data with theoretical models of galaxy evolution, the team reaches the remarkable conclusion that IRAC infrared observations can indeed distinguish the two groups in about 80% of the cases. The result implies that the two mechanisms (star formation or an active nuclear black hole) are typically not both simultaneously at work in these galaxies. That means that as galaxies evolve, transitions between the two stages of life must occur relatively quick in cosmic terms, less than about a few hundred million years. Not least, the team concludes that the new Spitzer "Warm Mission," which begins next spring with only IRAC and two of its detectors working, should be able to make many more such determinations with relative ease.

SUNRISE telescope delivers spectacular pictures of the Sun's surface

KATLENBURG-LINDAU, GERMANY (Nov. 11, 2009) – The Sun is a bubbling mass. Packages of gas rise and sink, lending the sun its grainy surface structure, its granulation. Dark spots appear and disappear, clouds of matter dart up - and behind the whole thing are the magnetic fields, the engines of it all. The SUNRISE balloon-borne telescope, a collaborative project between the Max Planck Institute for Solar System Research in Katlenburg-Lindau and partners in Germany, Spain and the USA, has now delivered images that show the complex interplay on the solar surface to a level of detail never before achieved.

FIGURE CAPTION – The IMaX instrument not only depicts the solar surface, it also makes magnetic fields visible; these appear as black or white structures in the polarised light. SUNRISE enables tiny magnetic fields on the surface of the Sun to be measured at a level of detail never before achieved.

The largest solar telescope ever to have left Earth was launched from the ESRANGE Space Centre in Kiruna, northern Sweden, on June 8, 2009. The total equipment weighed in at more than six tons on launch. Carried by a gigantic helium balloon with a capacity of a million cubic metres and a diameter of around 130 metres, SUNRISE reached a cruising altitude of 37 kilometres above the Earth's surface.

The observation conditions in this layer of the atmosphere, known as the stratosphere, are similar to those in outer space: for one thing, the images are no longer affected by air turbulence; and for another, the camera can also zoom in on the Sun in ultraviolet light, which would otherwise be absorbed by the ozone layer. After separating from the balloon, SUNRISE parachuted safely down to Earth on June 14th, landing on Somerset Island, a large island in Canada's Nunavut Territory situated in the Northwest Passage, the seaway through the Arctic Ocean between the Atlantic and the Pacific.

The work of analysing the total of 1.8 terabytes of observation data recorded by the telescope during its five-day flight has only just begun. Yet the first findings already give a promising indication that the mission will bring our understanding of the Sun and its activity a great leap forward. What is particularly interesting is the connection between the strength of the magnetic field and the brightness of tiny magnetic structures. Since the magnetic field varies in an eleven-year cycle of activity, the increased presence of these foundational elements brings a rise in overall solar brightness - resulting in greater heat input to the Earth.

The variations in solar radiation are particularly pronounced in ultraviolet light. This light does not reach the surface of the Earth; the ozone layer absorbs and is warmed by it. During its flight through the stratosphere, SUNRISE carried out the first ever study of the bright magnetic structures on the solar surface in this important spectral range with a wavelength of between 200 and 400 nanometres (millionths of a millimetre).

"Thanks to its excellent optical quality, the SUFI instrument was able to depict the very small magnetic structures with high intensity contrast, while the IMaX instrument simultaneously recorded the magnetic field and the flow velocity of the hot gas in these structures and their environment," says Dr. Achim Gandorfer, project scientist for SUNRISE at the Max Planck Institute for Solar System Research.

Previously, the observed physical processes could only be simulated with complex computer models. "Thanks to SUNRISE, these models can now be placed on a solid experimental basis," explains Prof. Manfred Schüssler, solar scientist at the MPS and co-founder of the mission.

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In addition to the Max Planck Institute for Solar System Research, numerous other research facilities are also involved in the SUNRISE mission: the Kiepenheuer Institute for Solar Physics in Freiburg, the High Altitude Observatory in Boulder (Colorado), the Instituto de Astrofisica de Canarias on Tenerife, the Lockheed-Martin Solar and Astrophysics Laboratory in Palo Alto (California), NASA's Columbia Scientific Ballooning Facility and the ESRANGE Space Centre. The project is funded by the Federal Ministry of Economics through the German Aerospace Centre (DLR).

[NK / HOR]

Star Formation

Stars form as gravitational forces coalesce the gas and dust in interstellar clouds until the material forms clumps dense enough to become stars. But how this happens, and whether or not the processes are the same for all stars remains very uncertain. Astronomers have been studying those clumps, the stellar wombs called "pre-stellar cores," in an attempt to sort out these questions. But precisely because the cores have no stars in them yet, or at best only very young stars, they are faint and difficult to study.

SAO astronomers Erik Rosolowsky and Phil Myers, together with four of their colleagues, have completed the first unbiased census of 200 cores in three relatively nearby clouds of gas and dust. They combined observations from a millimeter wavelength study with their infrared images from the Spitzer Space telescope. The former observations are able to identify the dense material (dense in this case means about 20,000 molecules per cubic centimeter), while the latter can probe inside the clumps for any evidence of warming, thereby signifying the presence of a young star.

Their findings are striking. First, the cores without embedded stars are not all the same, but come in a least two types. In one cloud they are larger in size but with the same mass as the cores that do have stars, while in the other case they are smaller and have less mass than cores with stars. This presumably means that cores in the second category will one day end up making smaller stars. Even more notable, the scientists report that when considered all together, the starless cores have a distribution of masses that is remarkably similar to the distribution of the masses of stars themselves. This finding strongly suggests that the masses of stars are determined by the masses of the cores from which they form and not, for example, by subsequent processes like random fragmentation that might take place after the cores develop.

The astronomers reach once more significant conclusion. Because the sample is about equal in the numbers of cores that have or do not have a embedded star, the team's analysis concludes that the lifetimes of the two cases should be comparable. Once a star forms in a core, it blows away the placental material, and emerges in a few hundred thousand years, and so the pre-stellar cores must also be only a few hundred thousand or so years old. And that means that late stages of the actual birth process is not slow and gradual ("quasi-static" is the technical term), but instead moves in a dynamic way towards the birth of a new star.

Exoplanet: Atmosphere

An "exoplanet" is an extra-solar planet, that is, a planet orbiting a star other than our own sun. Of the roughly 307 currently known extrasolar planets, about thirty of them transit their star (that is, their orbits take them in front of their star as seen from earth). Because an exoplanet is so faint as compared to its their respective sun, and usually also appear so close to it in the sky, its light is extremely difficult to measure. Astronomers trying to better understand all planets, including the earth, have, however, recently been able to measure useful limits to the reflected light of an exoplanet (see the SAO Science Weekly of 16 July 2008), and thereby to conclude, at least in this case, that its upper atmosphere probably does not contain clouds.

SAO astronomer Joe Hora, together with five of his colleagues, has used the Infrared Array Camera (IRAC) on the Spitzer Space Telescope to probe even further into the nature of the atmosphere of an exoplanet. The team studied the transiting exoplanet known as XO-1b as it passed behind its star in a series of so-called "secondary eclipses." IRAC's resolution is unable to spatially distinguish the planet from the star, but its detectors were able to detect the drop in total flux as the planet disappeared behind the star, and the increase when it emerged. Careful analysis at four infrared wavelengths revealed that the planet has noticeably more infrared emission than would be expected from a cloudless planet. The data are consistent with models in which the stratosphere of XO-1b contains absorbing gas or dust, and in which the atmosphere has a layer with warm vapor emitting in the infrared. The results not only improve our understanding of this particular exoplanet, they demonstrate the power of new infrared technology while helping us understand the nature of the atmospheres of planets far away.

Colliding Galaxies: Double Nuclei

The galaxy Arp 220 is actually two galaxies that have been caught in the act of merging. Astronomers think that many galaxies, including our own Milky Way, have undergone similar collisions during their histories. Although the process of galaxy collision is important and common, what happens during these encounters is not very well understood. For example, it seems likely that massive black holes (or perhaps binary black hole pairs) will form during the interactions, as the two galaxies' nuclei approach each other. Watching the process unfold helps scientists understand the evolution of the Milky Way, and, for that matter, the morphologies and distributions of galaxies throughout the universe. Arp 220, at a distance from earth of only about 250 million light years, and with a luminosity equal to that of about a trillion suns, has become the prototype for studying the merger process.

A team of seven SAO astronomers, Kazushi Sakmoto, Junzhi Wang, Martina Wiedner, Zhong Wang, Alison Peck, Qizhou Zhang, Paul Ho, and David Wilner, and a colleague, used the Submillimeter Array (SMA) to probe the two nuclei in Arp 220. The unequaled spatial resolution of the SMA at submillimeter wavelengths allowed the team to study the gas and dust in regions small enough to discover embedded structures. Indeed, they report that the dual nuclei are surrounded by a disk of gas a few thousand light-years in size, and that one of these nuclei contains warm dust apparently heated by nearby supernovae, consistent with there being active star formation present. The other nucleus, however, is different -- it is more compact, luminous, and its black hole seems to be actively accreting material (although an unusual kind of massive starburst might also explain the observations). The new results are a dramatic demonstration of the power of high spatial resolution studies at submillimeter wavelengths, and reveal the complex interactions, star forming activity, and black hole processes that can occur when galaxies collide.

Double Jets in Young Binary Stars

Most stars the size of the sun or larger (in mass) are part of multiple stellar systems in which two or even three stars orbit around one another. This tendency presumably reflects the conditions that existed when stars were born, since it is unlikely that stars pair up later on in their lives. The local conditions during star formation in turn reveal the complex environments when planets (if there are any) form around these stars. Binary stars might tend to disrupt the formation of any planets around them, for example.

Star birth is typically accompanied by the production of narrow bipolar jets of gas that shoot out perpendicular to the (possibly protoplanetary) disks around the young stars. These jets of material provide important diagnostics of the young stars and their environments, and multiple stars should, it is thought, have multiple jets. But although multiplicity is common in young stellar nurseries, it has been extremely difficult to study multiple jets in such systems -- very high spatial resolution millimeter (or submillimeter) wavelength studies are necessary to disentangle the multiple streams of gas.

The Submillimeter Array (SMA) is uniquely capable of making just such precise spatial measurements of jets, and a team of two SAO astronomers, Xuepeng Chen and Tyler Bourke, along with two colleagues, have now done so. They studied a young binary system about 1200 light-years away; the two stars are separated by about 8700 astronomical units (one AU is equivalent to the average distance of the earth from the sun). Writing in last week's Astrophysical Journal Letters, the team reports mapping two jets, one from each star. They find that the jets are nearly perpendicular to each other, with the two flows apparently independent of each other. They also find that the more massive star in the pair has the more massive outflow, perhaps because it has a more massive disk that helps generate the outflow. Equally interesting, their results demonstrate that jets in binaries -- and so protostellar disks -- are not necessarily co-aligned with each other after the binary stars are produced. Why this should happen remains one of the important questions to be studied in future research.

X-ray Jets

The longest known collimated structures in the universe are the narrow jets that emanate from vicinity of powerful black holes in certain types of galactic nuclei. These narrow beams can stretch across millions of light-years, and they transport huge amounts of energy from the nuclear black hole regions into intergalactic space. The jets were discovered at radio wavelengths, but more recently have been found to emit at X-ray wavelengths as well. The X-ray emission is thought to be produced principally by one of two mechanisms that involve the highly energetic electrons in the jet: either their scattering of the light of the cosmic microwave background radiation (the CMBR - the remnant light of the big bang), or their radiating in the presence of strong magnetic fields. Each mechanism sheds light on the nature of the driving source(s) around the black hole, and the environment in which the jets develop. But so far many aspects of these X-ray jets remain controversial, leaving the nature of the most dramatic cosmic phenomenon very uncertain.

Two SAO astronomers, Dan Harris and Aneta Siemiginowska, together with eight of their colleagues, have used the Chandra X-ray Observatory to probe the X-ray emission from the million-light-year-long bipolar jet in the galaxy 3C353. They have, for the first time, been able to detect the X-ray emission all along the jet and its numerous knots of activity, as well as around the nucleus itself. In particular, they discover X-ray emission from the jet on both sides of the nucleus. Although the predominant view has been that X-ray emission in this object's jets arises from CMBR scattering, the new results strongly disagree with this model because it predicts that the scattering will only be seen from the jet on the near side. The data point instead to the importance of magnetic field effects. When compared with data at radio wavelengths, the results also imply that the several knots could have been ejected from the nucleus, and that the local, small-scale environment of the jet (not just the large-scale environment) is critically important. Although many mysteries remain, these new results have corrected a basic misunderstanding about these dramatic cosmic structures, at least in this one powerful galaxy.

Water in Space

In 1998, a NASA team led by SAO astronomers launched a space mission to study water in space (and some other key molecules and atoms as well). The satellite, the Submillimeter Wave Astronomy Satellite (SWAS), successfully completed its primary mission in 2005. SWAS found water nearly everywhere it looked, and its data prompted SAO scientists to conclude that at least this requirement for life was present throughout the cosmos. But there was one outstanding puzzle lurking in SWAS's discovery of water: there was less of it (in relation to other molecules) than had been expected.

Since water is critical to life, astronomers want to understand not only where it is, but how much exists, and why. One solution to the puzzle subsequently proposed by the team was that considerable amounts of water are frozen out onto the surfaces of cold grains of dust where the molecules could not be detected by SWAS.

SAO astronomers from the SWAS team, Gary Melnick and Volker Tolls, along with six colleagues, have recently obtained new results from the Spitzer Space Telescope that suggest another option for water: it is very hot. Their data are the first detections of extended, hot water vapor with high spatial resolution imaging. SWAS, although it too had concluded there was hot water present, did not have the spatial resolution needed to quantify that conclusion. The astronomers looked at a region of young star formation with fast-moving, bi-polar jets of ejected material. Those jets produce shocks that have two effects on water -- they can evaporate the ice from surfaces of dust grains, and they can heat the water to temperatures as high as 1500 degrees kelvin. The new results show that, at least in some regions, the total amount of water agrees with that predicted by chemical models to within the uncertainties, and lend confidence to our general understanding of this vital constituent of the cosmos.

Epsilon Eridani: a Young Solar System

When the first infrared cosmic survey satellite, IRAS, looked at the nearby star Epsilon Eridani in 1984, it found that the star emitted a large excess of cool infrared radiation. This star is only 10.5 light-years from earth, and had already been carefully examined at optical wavelengths. Those studies had showed that it is quite similar to our sun in mass, but is much younger -- only about 850 million years old versus the sun's age of 4.5 billion years. When the sun was as young as Epsilon Eridani we think it was in the process of forming its system of planets. The discovery of strong excess infrared emission, therefore, immediately suggested that the star had a disk of preplanetary dust around it, and this dust was the source of the excess infrared.

That conclusion has since been confirmed by other observations, and moreover other stars have been discovered with preplanetary, infrared-emitting disks around them. But Epsilon Eridani remains a pivotal example because it is near enough to us to allow close scrutiny. Last week a team of twelve astronomers including CfA astronomers Massimo Marengo, David Wilner, Tom Megeath and Giovanni Fazio announced the results of their combined infrared and submillimeter wavelength study of the dust disk in Epsilon Eridani. They used five different instruments to probe the nature of the emission. They find clear evidence that the disk consists of three separate rings: an "asteroid belt" similar to the one in our solar system about three astronomical units (AU) away from the star, a second "asteroid belt" about seven times farther out than the first and unlike anything in our solar system, and a third, previously-known icy ring of material at 35 to 100 AU away from the star with about 100 times as much material as is in our solar system's outer reservoir ring.

The new results also find gaps between these rings. These gaps were created, the scientists suggest, by the presence of otherwise unseen planets that cleared out the material in their orbits. The overall picture suggests a very early analog to our solar system in which three planets with masses between those of Jupiter and Saturn clear out rings in the young circumstellar disk. The disk is probably made mostly of silicate and ice dust grains that are short lived, and so must be constantly regenerated from collisions between larger, perhaps kilometer-sized, objects in the outer ring. This paper is an important step in our understanding of how the early solar system may have formed and evolved.

'Dropouts' Pinpoint Earliest Galaxies

PASADENA, CA (Nov. 9, 2009) – Astronomers, conducting the broadest survey to date of galaxies from about 800 million years after the Big Bang, have found 22 early galaxies and confirmed the age of one by its characteristic hydrogen signature at 787 million years post Big Bang. The finding is the first age-confirmation of a so-called dropout galaxy at that distant time and pinpoints when an era called the reionization epoch likely began. The research will be published in a December issue of the Astrophysical Journal.

FIGURE CAPTION – This is a composite of false color images of the galaxies found at the early epoch around 800 million years after the Big Bang. The upper left panel presents the galaxy confirmed in the 787 million year old universe. These galaxies are in the Subaru Deep Field. (Credit: These images are created by M. Ouchi et al., which are the reproduction of Figure 3 in the Astrophysical Journal December 2009 issue.)

With recent technological advancements, such as the Wide-Field Camera 3 on the Hubble Space Telescope, there has been an explosion of research of the reionization period, the farthest back in time that astronomers can observe. The Big Bang, 13.7 billion years ago, created a hot, murky universe. Some 400,000 years later, temperatures cooled, electrons and protons joined to form neutral hydrogen, and the murk cleared. Some time before 1 billion years after the Big Bang, neutral hydrogen began to form stars in the first galaxies, which radiated energy and changed the hydrogen back to being ionized. Although not the thick plasma soup of the earlier period just after the Big Bang, this star formation started the reionization epoch. Astronomers know that this era ended about 1 billion years after the Big Bang, but when it began has eluded them and intrigued researchers like lead author Masami Ouchi of the Carnegie Observatories.

The U.S. and Japanese team led by Ouchi used a technique for finding these extremely distant galaxies. “We look for ‘dropout’ galaxies,” explained Ouchi. “We use progressively redder filters that reveal increasing wavelengths of light and watch which galaxies disappear from or ‘dropout’ of images made using those filters. Older, more distant galaxies ‘dropout’ of progressively redder filters and the specific wavelengths can tell us the galaxies’ distance and age. What makes this study different is that we surveyed an area that is over 100 times larger than previous ones and, as a result, had a larger sample of early galaxies (22) than past surveys. Plus, we were able to confirm one galaxy’s age,” he continued. “Since all the galaxies were found using the same dropout technique, they are likely to be the same age.”

Ouchi’s team was able to conduct such a large survey because they used a custom-made, super-red filter and other unique technological advancements in red sensitivity on the wide-field camera of the 8.3-meter Subaru Telescope. They made their observations from 2006 to 2009 in the Subaru Deep Field and Great Observatories Origins Deep Survey North field. They then compared their observations with data gathered in other studies.

Astronomers have wondered whether the universe underwent reionization instantaneously or gradually over time, but more importantly, they have tried to isolate when the universe began reionization. Galaxy density and brightness measurements are key to calculating star-formation rates, which tell a lot about what happened when. The astronomers looked at star-formation rates and the rate at which hydrogen was ionized.

Using data from their study and others, they determined that the star-formation rates were dramatically lower from 800 million years to about one billion years after the Big Bang, than thereafter. Accordingly, they calculated that the rate of ionization would be very slow during this early time, because of this low star-formation rate.

“We were really surprised that the rate of ionization seems so low, which would constitute a contradiction with the claim of NASA’s WMAP satellite. It concluded that reionization started no later than 600 million years after the Big Bang,” remarked Ouchi. “We think this riddle might be explained by more efficient ionizing photon production rates in early galaxies. The formation of massive stars may have been much more vigorous then than in today’s galaxies. Fewer, massive stars produce more ionizing photons than many smaller stars,” he explained.

http://www.ciw.edu/prouchiz7falsecolornotype_jpg

Plot of ionization history http://www.ciw.edu/prouchiz7galaxyionizationhist_jpg

Cosmic star-formation history http://www.ciw.edu/prouchiz7galaxyageplots_jpg

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The work was funded by the Carnegie Institution. The research is based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the Hubble Space Telescope, operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555; the Spitzer Telescope, managed by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

Dusty Gobules

New stars tend to form with disks of gas and dust around them. After a few hundred thousand years or so, the intense ultraviolet radiation from the most massive of these stars has expelled much of the gas in the outer portion of the nearby disks, and scientist think that the escaping gas takes some of the dust along with it. That dust can be seen at infrared wavelengths as cool, comet-shaped globules. Since these disks are the birthplaces of planets, the processes involved in producing globules will impact the formation and subsequent evolution of planets. Hence astronomers are very interested in the diagnostic clues provided by cometary globules.

The Spitzer Space Telescope with its infrared cameras is able to study many of these dim cometary globules for the first time. Three SAO astronomers, Xavier Koenig, Lori Allen, and Scott Kenyon, along with two colleagues, have imaged the giant star forming region called W5 over an area in the sky about the size of four full moons, and discovered four such globules. They report in this week's Astrophysical Journal Letters that their data indicate the dust in these globules was not completely removed with the gas.

Instead, the dust appears to have remained in the disk but only later was blown out by radiation pressure from the nearest massive star. The difference is important because of the new timescale it implies. Rather than being removed from the disk with the gas in tens of thousands of years, as had once been suggested, the new results suggest that the dust can survive in the disk for a few million years. Planets, after they form from these disks, can migrate inward towards their star on a timescale of hundreds of thousands of years. These new results address the environment of planets during this early phase of their evolution.

Colliding Galaxies in the Early Universe

The universe contains many fabulously luminous galaxies, some of them more than a thousand times brighter than our own Milky Way. Most of them are practically invisible at optical wavelengths, however, because their light is predominantly at infrared wavelengths, and comes not from stars but from warm dust. Astronomers are quite sure that the energy to heat the dust comes from giant bursts of star formation that are hidden from optical view by the dust itself, but they do not know what triggers these bursts. These bright objects have been detected in the very early universe, prompting speculation that perhaps our own Milky Way is in some ways descended from galaxies like them.

Galaxies frequently collide with one another, and evidence for their stupendous interactions is found from their distorted shapes and their bright infrared emission. These collisions are thought to trigger the production of massive stars that heat the galactic dust. At least, that is what astronomers conclude from studying nearby interacting galaxies. More distant ones in the early universe, however, are so far away that such interactions are much harder to verify. Perhaps a massive black hole at the nucleus is responsible for the luminosity, in whole or in part?

A team of SAO astronomers, Steve Willner, Mark Gurwell, and Matt Ashby, along with six of their colleagues, have used the Submillimeter Array and other observing facilities to see for the first time the spatial geometry of a bright galaxy so old that its light has been en route to us for over eleven billion years, nearly 80% of the age of the universe. The object had been known because of its powerful radio wavelength emission, thought to be the result of a massive black hole.

The team discovered that the source is actually two bright objects, consistent with the idea of two galaxies in collision. Surprisingly, they found that the two sources are slightly offset from the bright radio source. They concluded that the system consists of two colliding galaxies and a bridge of warm material between them, produced by their collision. Their data reveal one galaxy and the bridge; the other galaxy is hidden even at infrared and submillimeter wavelengths but is seen with the radio data. The results contradict the commonly held view that a black hole nucleus is responsible for both the radio and the luminous infrared emission in distant galaxies -- at least in this case the powerful infrared emission comes from a burst of new stars.

Shedding Light on the Cosmic Skeleton

GARCHING, GERMANY (Nov. 6, 2009) – Astronomers have tracked down a gigantic, previously unknown assembly of galaxies located almost seven billion light-years away from us. The discovery, made possible by combining two of the most powerful ground-based telescopes in the world, is the first observation of such a prominent galaxy structure in the distant Universe, providing further insight into the cosmic web and how it formed.

“Matter is not distributed uniformly in the Universe,” says Masayuki Tanaka from ESO, who led the new study. “In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called ‘cosmic web’, in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure.”

These filaments are millions of light years long and constitute the skeleton of the Universe: galaxies gather around them, and immense galaxy clusters form at their intersections, lurking like giant spiders waiting for more matter to digest. Scientists are struggling to determine how they swirl into existence. Although massive filamentary structures have been often observed at relatively small distances from us, solid proof of their existence in the more distant Universe has been lacking until now.

The team led by Tanaka discovered a large structure around a distant cluster of galaxies in images they obtained earlier. They have now used two major ground-based telescopes to study this structure in greater detail, measuring the distances from Earth of over 150 galaxies, and, hence, obtaining a three-dimensional view of the structure. The spectroscopic observations were performed using the VIMOS instrument on ESO’s Very Large Telescope and FOCAS on the Subaru Telescope, operated by the National Astronomical Observatory of Japan.

Thanks to these and other observations, the astronomers were able to make a real demographic study of this structure, and have identified several groups of galaxies surrounding the main galaxy cluster. They could distinguish tens of such clumps, each typically ten times as massive as our own Milky Way galaxy — and some as much as a thousand times more massive — while they estimate that the mass of the cluster amounts to at least ten thousand times the mass of the Milky Way. Some of the clumps are feeling the fatal gravitational pull of the cluster, and will eventually fall into it.

“This is the first time that we have observed such a rich and prominent structure in the distant Universe,” says Tanaka. “We can now move from demography to sociology and study how the properties of galaxies depend on their environment, at a time when the Universe was only two thirds of its present age.”

The filament is located about 6.7 billion light-years away from us and extends over at least 60 million light-years. The newly uncovered structure does probably extend further, beyond the field probed by the team, and hence future observations have already been planned to obtain a definite measure of its size.

More Information

This research was presented in a paper published as a letter in the Astronomy & Astrophysics Journal: The spectroscopically confirmed huge cosmic structure at z = 0.55, by Tanaka et al.

The team is composed of Masayuki Tanaka (ESO), Alexis Finoguenov (Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany and University of Maryland, Baltimore, USA), Tadayuki Kodama (National Astronomical Observatory of Japan, Tokyo, Japan), Yusei Koyama (Department of Astronomy, University of Tokyo, Japan), Ben Maughan (H.H. Wills Physics Laboratory, University of Bristol, UK) and Fumiaki Nakata (Subaru Telescope, National Astronomical Observatory of Japan).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Rapid supernova could be new class of exploding star

BERKELEY, CA (Nov. 5, 2009) — An unusual supernova rediscovered in seven-year-old data may be the first example of a new type of exploding star, possibly from a binary star system where helium flows from one white dwarf onto another and detonates in a thermonuclear explosion.In a paper first published online Nov. 5 in the journal Science Express, University of California, Berkeley, and Lawrence Berkeley National Laboratory (LBNL) astronomer Dovi Poznanski and his colleagues describe the outburst, dubbed SN 2002bj, and why they believe it is a new type of explosion.

FIGURE CAPTION – Artist's impression of an AM-CVn star system, where helium flows from one star, a helium white dwarf (upper right), onto another, piling up in an accretion disk around a small, dense primary star. Helium from the disk eventually falls onto the star, forming a shell that may end up exploding as a Type .Ia (point one A) supernova.

"This is the fastest evolving supernova we have ever seen," said Poznanski, a UC Berkeley post-doctoral fellow who recently joined LBNL's Computational Cosmology Center. "It was three to four times faster than a standard supernova, basically disappearing within 20 days. Its brightness just dropped like a rock."

This rapid drop, coupled with the supernova's faintness, the strong signature of helium in the spectrum of the explosion, the absence of hydrogen, and the possible presence of vanadium – an element never previously identified in supernova spectra – points toward helium detonation on a white dwarf, the astronomers said.

"We think this may well be a new physical explosion mechanism, not just a minor variation of ones already known," said co-author Alex Filippenko, UC Berkeley professor of astronomy. "This supernova is qualitatively different from the complete disruption of a white dwarf, known as a Type Ia supernova, or the collapse of an iron core and rebound of the surrounding material, so-called 'core-collapse supernovae.'"

Co-author Joshua Bloom, UC Berkeley associate professor of astronomy, also views SN 2002bj as a "new beast" quite different from the two well-known classes of supernovae.

"We have seen great diversity in those two main supernova mechanisms, but even within that diversity, observationally, there is a limited range of variation spectrally and in how events evolve in time," he said. "This object (SN 2002bj) falls outside that range."

The supernova was detected in 2002 in the galaxy NGC 1821, in the constellation Lepus, by Filippenko's Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory near San Jose as well as by amateur astronomers. Due to an unfortunate alignment of circumstances, the supernova was erroneously classified by the astronomical community as a common Type II supernova and filed away.
In June, Poznanski happened upon the spectrum while searching for Type II supernovae he hopes to use as distance indicators to confirm the accelerating expansion of the universe. When he carefully examined a high-quality spectrum of SN 2002bj, he realized that the supernova was not a Type II at all, but an unusual kind of supernova more akin to a Type Ia.

The spectrum had been obtained seven days after its discovery by Filippenko and Douglas Leonard, at the time a UC Berkeley graduate student, now an assistant professor of astronomy at San Diego State University, using the Keck I telescope.

"Its classification was a mistake, which is understandable given the conditions of the data. But, of course, a redress of old data with fresh eyes is not usually this fruitful," Leonard said.

Pulling out follow-up images made by KAIT, Poznanski and UC Berkeley graduate student Mohan Ganeshalingam found that the brightness of SN 2002bj dropped off so rapidly that the supernova disappeared 20 days after its discovery. An image of that area of the sky taken seven days prior to its discovery showed no supernova, so it had brightened and dimmed into obscurity in less than 27 days, whereas most supernovae brighten and dim over three to four months.

Searching through thousands of supernovae spectra, Poznanski and graduate student Ryan Chornock – now a post-doctoral fellow at Harvard University – could find none that had such an awkward composition, but they did come across a theory of fast but faint supernovae that seemed to fit.

Proposed by Lars Bildsten and colleagues – Bildsten is a professor of physics at the Kavli Institute for Theoretical Physics at UC Santa Barbara – the theory involves AM Canum Venaticorum (AM CVn) binary systems, which are composed of two white dwarfs, one of which is primarily made of helium that is being slowly pulled by gravity onto its companion. White dwarfs are the remnants of stars that burned their hydrogen down to carbon and oxygen or, in some particular cases, to helium.

In a 2007 Astrophysical Journal Letters paper, Bildsten and colleagues proposed that in AM CVn systems, when enough helium has been accumulated on the surface of the primary white dwarf, an explosion will occur that can "power a faint … and rapidly rising (few days) thermonuclear supernova."

Christopher Stubbs, chair of the Department of Physics at Harvard University, jokingly dubbed it a ''.Ia'' (point one A) supernova, because it is one-tenth as bright for one-tenth the time as a Type Ia supernova, and the name stuck.

Filippenko noted that this explosion is nothing like a regular Type Ia explosion because the white dwarf survives the detonation of the helium shell. In fact, it has similarities to both a nova and a supernova. Novas occur when matter – primarily hydrogen – falls onto a star and accumulates in a shell that can flare up as brief thermonuclear explosions. SN 2002bj is a "super" nova, generating about 1,000 times the energy of a standard nova, he said.

The explosion would have created heavy elements such as chromium, which decays to vanadium and thence to titanium. Thus, absorption lines of vanadium could be expected, Poznanski said.

Filippenko noted that the past few years have "yielded a bonanza of weird supernovae."

"A lot of us who have studied supernovae for several decades are amazed at the quality and quantity of data coming in recently, showing interesting new subclasses or even strange new physical classes of supernovae," he said. "It whets my appetite for what else we might find out there with these large, wide-sky surveys like the Palomar Transient Factory, Dark Energy Survey and the Large Synoptic Survey Telescope. KAIT has discovered about 800 supernovae, but these new surveys will find thousands or hundreds of thousands of supernovae."

Poznanski, too, is expecting the current Palomar Transient Factory, which uses a wide-field camera to search the sky daily for new objects, to find more supernovae like SN 2002bj. The factory is a project led by Shri Kulkarni, professor of astronomy at the California Institute of Technology (Caltech), and involves many of the co-authors on the Science Express paper, including Peter Nugent, co-leader of the Computational Cosmology Center at LBNL, who runs the search for transients.

"The Palomar survey will be able to find many rare objects, like SN 2002bj, by scanning huge parts of the sky and not limit itself to the big, bright and nearby galaxies," Poznanski said.

Coauthors with Poznanski, Filippenko, Nugent, Ganeshalingam, Leonard, Chornock and Bloom are Rollin C. Thomas, a member of the Computational Cosmology Center, and Weidong Li of UC Berkeley's Department of Astronomy.

The research was funded by the National Science Foundation, the Department of Energy, the Sylvia and Jim Katzman Foundation and the TABASGO Foundation, with observational assistance from the University of California Lick Observatory and the W. M. Keck Observatory in Hawaii.

By Robert Sanders, Media Relations

Ultra-Luminous Infrared Galaxies

Ultraluminous infrared galaxies ("ULIRGs") shine with the luminosity of one hundred or more Milky Way galaxies. Their most striking feature, however, is not their tremendous energy output but the fact that nearly all of their radiation is invisible, lying at infrared wavelengths. The source of this energy is intense star formation, and because that activity takes place within dust-filled clouds, the ultraviolet and visible light generated is absorbed by the dust grains and remitted in the infrared.

ULIRGs are thought to result from collisions between galaxies, and since collisions are common, ULIRGs and the slightly dimmer "luminous infrared galaxies" may represent a period of stellar growth and enrichment that many galaxies (perhaps even our own galaxy) briefly experience, especially at early times in the age of the universe when collisions were common. The connections between galaxy interactions and star formation, however, are poorly understood, in part because the obscuring dust makes it difficult to probe the small nuclei of the two merging galaxies.

SAO astronomers Christine Wilson, Glen Petitpas, Daisuke Iono, Alison Peck, Melanie Krips, and Tom Cox, together with ten colleagues, have just published the first in a landmark series of papers on luminous and ultraluminous galaxies using data obtained with SAO's Submillimeter Array (SMA). The SMA allowed the astronomers to measure for the first time the spatial distribution of the warm gas around luminous galaxies' nuclei.

The scientists reached two surprising conclusions. First, they found that the ratio of the amount of gas to dust is about the same as it is in the Milky Way despite the very different level of star formation activity. Second, they discovered that it is peak gas density, not the peak gas mass, that correlates with the region of maximum brightness. This suggests that the increased rate of star birth is the result of increased availability of molecular gas as the fuel, a conclusion that is in direct contrast to the conventional wisdom that abundant gas increases the efficiency but not the rate of star birth. The new paper, the first in a set that will analyze fourteen nearby galaxies, pioneers new, high spatial resolution diagnostics to provide new insights into these powerful cosmic beacons.

Hot Jupiter Atmospheres

Of the 300 or so extra-solar planets known, twenty-eight have been found because they transit their star (that is, their orbits take them in front of their star as seen from earth). An exoplanet is faint as compared to its respective sun (about one thousand times fainter, depending on the wavelength) and so its light is very difficult to measure. But the sensitive and stable Infrared Array Camera (IRAC) on the Spitzer Space Telescope, and its longer wavelength partner, the Multiband Imaging Photometer (MIPS), can do just that.

David Charbonneau, Heather Knutson, and Lori Allen, along with five colleagues, have used IRAC and MIPS to study the transiting exoplanet system HD 189733b in five infrared wavelength bands. The planet was already known to be a "hot Jupiter," that is, a planet with about the same mass as Jupiter but which orbits so close to its star that (unlike Jupiter in our solar system) its atmosphere is very hot - over 1000K in some cases.

The scientists saw the planet pass behind its star twice in over 23,000 snapshots obtained during the transits. Their analysis shows clear excess radiation in one band, indicating that the atmosphere of the exoplanet probably has water and carbon monoxide gas. They also conclude that the atmosphere has a temperature inversion, meaning that the temperature actually increases with altitude over some range, instead of simply dropping with altitude. An inversion often signals the presence of other gases in the atmosphere and particular kinds of illumination from the sun. The significance of this result is that other hot Jupiters have been found with no signs of inversion. As a result, the new paper establishes that hot Jupiters diverge into at least two classes, and takes a dramatic step in showing that extra-solar planets form a very diverse set, with even the case of hot Jupiters being more complex than originally supposed. The emerging discipline of exoplanet research promises to provide new insights into the atmospheres of all planets.

Circumstellar Gas Shells

The second brightest object in the sky outside of our solar system is the variable star CW Leo, located about 450 light-years away in the direction of the constellation of Leo (the brightest object in the sky is the southern hemisphere star called Eta Carina). CW Leo is barely visible at optical wavelengths, however, because its tremendous luminosity is emitted mostly in the infrared.

CW Leo is famous not only because it is so bright, but because it has already burned most of its hydrogen and much of its helium fuel, and in the process has produced shells of dust around the star rich in molecules, with over sixty species identified, many of them organic. In fact, the well documented, layered cocoons of dust and gas are the result of the star's ejecting about one earth-mass of material per year. CW Leo may be unusually bright, but it is nonetheless representative of the class of evolved stars in our galaxy which astronomers think are responsible for making and disbursing most of the dust and organic molecules in space. This dust is then a catalyst for more complex chemical reactions that occur, and also plays a pivotal role in preparing the interstellar medium for a next generation of stars. Astronomers are still trying to figure out, however, exactly how the star makes and blows away all this material.

SAO's Submillimeter Array (SMA) is the first facility capable of obtaining both very high spatial resolution imaging and precise velocity information at submillimeter wavelengths where many of these molecules emit their radiation. A team of nine SAO astronomers led by Nimesh Patel, along with two colleagues, have just published the first two articles in a pioneering series on the molecular envelope in CW Leo. These first papers report on the previously known sulfur-bearing molecules SiS and CS, and on CO. The first two are found to lie in a shell about sixty astronomical units from star, a distance where the ambient temperature is thought to have cooled enough for dust to solidify but where the stellar wind is still accelerating outward. The CO is discovered in an unusual, excited state indicating that it comes from much closer to the star, perhaps only a few astronomical units which, in the case of this kind of swollen evolved star, puts it very close to the star's photosphere itself. The results help to explain the detailed inner structure of the dust cocoons formed in evolved stars, and mark the beginning of a new probe of evolved stars.

Dark Energy

In 1998 two teams of astronomers, one of them led by CfA scientists, astonished the world with their announcement that the universe would expand forever. They soon added to the amazement by presenting evidence that the universe is not only expanding outward, it is accelerating outward. Their observations studied supernovae in galaxies so far away that their observed motions are primarily due to the expansion properties of the cosmos itself.

Two explanations are commonly advanced to explain the outward acceleration of the universe. The first asserts that, as Einstein once speculated, gravity itself causes objects to repel one another when they are far enough apart. This feature of gravity is described by general relativity with an arbitrary constant term, not fixed by first principles, commonly called the cosmological constant. The second explanation hypothesizes (based on our current understanding of elementary particle physics) that the vacuum has properties that provide energy to the cosmos for expansion. This energy was dubbed "dark energy," in poetic analogy to dark matter, the name given to the mysterious material that does not radiate light but reveals itself (so far at least) only via its gravitational influence on galaxies. (Dark matter is dark because it does not radiate light and is mysterious; dark energy is 'dark' only because it is mysterious.) Each of these two explanations for cosmic acceleration (which are often interchangeably referred to as dark energy) has its own set of ancillary implications that can be used to probe which one (or neither, or both) is correct.

At a news conference this week, CfA astronomers Alexey Vikhlinin, Bill Forman, Christine Jones, and Steve Murray, together with seven colleagues, announced dramatic new evidence for dark energy (their paper will appear in February). They studied the clustering of two sets of distant galaxies using X-ray observations from the Chandra X-ray Observatory and the ROSAT X-ray satellite. The two sets of clusters represent snapshots of the universe taken about four billion years apart, roughly one-third of the age of the universe. The team used sophisticated computer models to calculate how galaxies should cluster together during that time span if the accelerating cosmos were not dragging them apart. They find convincing evidence in their observations that the clustering is actually significantly less than this, but consistent with the presence of dark energy.

The new results provide the first independent, direct evidence for cosmic acceleration since the original discovery, based on distant supernovae, eleven years ago. It now looks increasingly certain that other suggested explanations for the supernova results are improbable; for example, proposals to modify Einstein's theory of relativity. The new results significantly narrow the options for key aspects of the cosmic expansion, including the putative mass of one very abundant but hard to detect particle, the neutrino. The team's results, by helping to confirm and clarify the nature of dark energy, have helped to make dark energy a little less dark.

X-rays from Young Stars

A newly-formed star usually has a disk of gas and dust around it. This disk (the source of possible future planets) can generate intense X-ray radiation as its material falls onto the star's surface. Indeed, X-ray emission from such stars has been seen and studied by the Chandra X-ray Observatory and other X-ray facilities. Besides being a powerful diagnostic of what is going on around the infant star, the radiation affects the chemistry in the disk, and can drive a hot wind that influences the morphology of the disk and its developing planets.

SAO astronomers Barbara Ercolano, Jeremy Drake, John Raymond, and a colleague of theirs have completed the first stage of a detailed computational code that models the hot gas around young stars. The sophisticated computation finds the X-ray emitting gas can reach temperatures of about one million kelvin near the star, and ten thousand kelvin at the distance of one AU (where a putative earth might be). They find that several atomic species are excited in these regions and should be observable with new telescopes, and they predict the intensities so that eventual comparisons can be used to refine their model. They also are able to predict mass-loss rates: about one-thousandth of an earth-mass per year, enough to disburse the disk in a few million years if the wind were to continue unabated.

The calculations were particularly complex because a wide range of temperatures had to be included in the model, from extremely hot to more normal values of a few thousand kelvin; the computations included effects of ultraviolet as well as X-ray radiation. Complicating the calculation, the disk itself rotates and evolves, and has a molecular component mixed in with the dust that must be considered. The team's result, a detailed characterization of the corona-like inner region of the hot disk around young stars, represents an important step in unraveling both the evolving structure of young disks, and how the hot inner regions of a young star affect the solar system under development.

Interview with British born astronaut Michael Foale

Astronomy Now interviews British born astronaut Michael Foale, who provides a fascinating account of "walking" in space, repairing the Hubble Space Telescope and viewing the Milky Way Galaxy from space.

Featured News

Keeping up-to-date with cutting-edge astronomy and space science breakthroughs has just become that much easier, thanks to the Portal To The Universe, the latest Cornerstone project of the International Year of Astronomy 2009 (IYA2009). As a high-tech website embracing Web 2.0 technologies, the Portal To The Universe aims to become a one-stop-shop for astronomy news:

Massive Star Formation

Astronomers think that most stars form in clusters because evidence suggests that a nursery capable of producing one star efficiently is usually capable of birthing many. But precisely how this happens is still unclear. If our own Sun, for example, had formed in such a cluster, where are its siblings? The molecular cloud NGC 6334, located about five thousand light-years from Earth, is apparently in the process of giving birth to two separate clusters of massive stars. Astronomers have reported two regions of activity, each with a total mass of a few hundred solar masses, each about the size of our solar system (measured at its cometary edges), and each with several young stars. Discoveries made by the Submillimeter Array (SMA) last year included small, star forming cores embedded in these regions in NGC 6334; astronomers are now probing these regions with other instruments to try to unravel more clues about how star clusters form.

Two SAO astronomers, Luis Zapata and Paul Ho, together with a colleague, have used radio telescopes to follow up the SMA results. They report finding elongated disks around four of the embedded stars, and are able to estimate the disks' masses. What they find is a surprise: in the few previous cases where disks have been adequately studied around such stars, they are typically ten times smaller in mass than the star itself. But in each of the four objects studied in NGC 6334, the disk appears to be more comparable to the star's mass. The authors note that young stars will grow in mass as they accrete material from the disk, and suggest that perhaps these stars are still very young. Theoretical modeling, while not accounting for all of the likely subtleties, indicates the range of masses seen in the NGC 6334 cores may be reasonable. The new results, therefore, suggest that these very young stars are still early in the process of growing, and that astronomers have succeeded in obtaining what might be considered an analog of a ultrasound scan of the stellar embryos in this interstellar womb.

SETI Search: Optimal Frequency

Not long after the big bang that created our universe, the cosmos had cooled enough for its matter -- mostly hydrogen -- to form neutral atoms. Astronomers know that neutral hydrogen emits characteristic radiation at a wavelength of 21 centimeters, and for over fifty years they have studied neutral gas in our galaxy using this tracer radiation. Now astronomers are planning to build large new radio telescopes to study the neutral hydrogen gas at the remote edges of our known universe, gas that dates back to the early ages of the universe. Such research will provide important information about the shape and character of clusters of matter a few hundred million years after the big bang, when the first stars and galaxies are thought to have developed. But the powerful new telescopes offer an interesting side benefit.

Two CfA astronomers, Avi Loeb and Matias Zaldarriaga, have just published an article showing that the search for extraterrestrial intelligence (SETI) -- that is, intelligent life on other planets in the local universe -- can benefit in important new ways from the new generation of radio telescopes. Up until now, the scientists note, SETI searches have relied on searches at wavelengths where radio technology was most effective, namely, wavelengths with sensitive detectors and very low background noise levels. Frequencies near television or other broadcast stations, for example, where the vast majority of our radio transmissions occur, were avoided.

The two astronomers point out that the telescopes designed to study the primordial neutral hydrogen will by chance be tuned to the wavelengths where our civilization, and so possibly other local civilizations, broadcast loudly. Furthermore, they note that the nature of the cosmological searches, requiring the study of wide swaths of the sky for long periods of time, are fortuitously suitable to locate and identify SETI sources (assuming they arise on planets whose rotation and revolution can be monitored and used to identify the signal as artificial). The astronomers outline some steps that can be taken to insure that the data are properly analyzed for SETI information. The paper is a good illustration of the serendipitous power of astronomical surveys, and the importance of taking creative advantage of powerful new technological tools.

Supernova Explosion

Supernovae, the explosive deaths of massive stars, disburse into space all of the chemical elements that were spawned inside the progenitor stars. Furthermore, these violent explosions themselves generate most of the elements above iron in the periodic table, and scatter them as well. Chemical enrichment alone makes supernovae immensely important contributors to the cosmic ecosystem. The class of supernova called "type Ia" offer yet another powerful advantage. These objects are produced when a dense, evolved star has a large companion star that gradually spills material onto its surface. Once the mass of the compact star exceeds a fixed, relatively well-defined limit, gravity triggers its explosive demise. Type Ia supernovae are thus thought to be "standard candles," and are used by astronomers to estimate the distances to remote galaxies whose supernovae appear faint because they are far away: they calibrate our cosmic distance scale.

Astronomers, precisely in order to get the best possible calibration, want to understand all the possible ways these supernova can erupt. Observers have naturally tended to discover and monitor supernovae near or after they have peaked in brightness, but models suggest that subtle, important differences between kinds of Type Ia progenitor stars are lost after their brightness peaks. A team of five CfA astronomers, Arti Garg, Chris Stubbs, Peter Challis, Michael Wood-Vasey, and Stephane Blondin, together with sixteen colleagues, have now measured the growing brightness of eleven Type Ia supernovae *before* they reached their intensity maxima.

The team has been imaging the Large Magellanic Cloud, a neighboring galaxy of ours, for five years, each season taking about twenty images of the same regions of the galaxy over a three month interval. Using techniques designed especially for discovering small intensity variations, the astronomers found they had data on eleven Type Ia supernovae before their intensities had peaked. These brightness curves show that it takes such an explosion about 17.6 days to reach a maximum brightness in the optical; previous estimates had thought this time frame was 21.1 days. The significance of the discrepancy to the calibration of distances is still uncertain, but what is clear is that the precise new data can help sort out competing models of Type Ia supernova explosions, and thus improve the reliability of the critical calibrations they provide.

Gamma-ray Bursts

Gamma ray bursts (GRBs), the brightest events in the known universe, are flashes of high-energy light that occur about once a day, randomly, from around the sky. While a burst is underway, it is many millions of times brighter than an entire galaxy. Astronomers are anxious to decipher their nature not only because of their dramatic energetics, but also because their tremendous brightnesses should enable them to be seen across cosmological distances and times.

The circumstantial evidence on GRBs to date suggests that radiation from the gigantic explosions is beamed (that is, it is not radiated uniformly in all directions), and that shocks from ultra-fast moving particles produce much of the emission. Some models predict that hours or days after the explosion itself more gamma rays are produced by shock activity; some of this radiation is expected to have particularly high energy, hundreds of thousands of times more than medical X-rays, for example.

Two SAO astronomers, Deirdre Horan and Trevor Weeks, led a team of fifty-nine scientists in a study of gamma-ray bursts using the ten-meter Whipple Telescope on Mt. Hopkins, Arizona, one of the few facilities in the world capable of studying such very high energy radiation. When a GRB event was detected by an orbiting satellite, the email announcement triggered a flurry of telescope activity; bursts fade quickly, after all, and putative aftershocks might only last for a day. The Whipple Telescope is in principal able to slew and stare at any part of the visible sky in only three minutes, and its rapid response makes it ideal for GRB research. Over a seventeen month period spanning 2003, it studied seven different GRBs. While not detecting any very high energy radiation from these seven bursts, its precision was able to set useful constraints on some of the models of GRB, and to refine techniques for future observations. Considering that GRBs produce the most dramatically energetic events in the universe, it is expected that these very high energy investigations will help to refine our understanding of physics and the nature of matter in extreme conditions.

Binary Star Formation

More than about half of all stars roughly similar to the Sun or larger (in mass) are part of multiple systems -- binary stars, or even triplets, that orbit around one another. This tendency reflects the conditions that existed when stars like the Sun were born, since most probably such stars were born as multiplets and did not pair up later on in their lives. The local conditions in turn reveal the prevailing environment when planets (if any) form. If, for example, orbiting binary stars tend to disrupt the formation of any planets around them, then our Sun's family of planets might be a rarer phenomenon than currently envisioned.

SAO astronomers Todd Hunter, David Wilner, Qizhou Zhang, and Paul Ho, along with six of their colleagues, have used SAO's Submillimeter Array (SMA) to probe a newly formed, massive star and its environment. The SMA, which can obtain very sharp images of cool dust and gas in the environment of young stars, revealed the presence of two clumps where a single star was thought to reside. But in principle these two objects might not be physically related.

In order to study the pair more carefully, the scientists had to utilize some clever technical tricks. Normally distant quasars are used as calibration objects for telescope arrays like the SMA that combine the light from multiple telescopes in order to achieve their precision -- but there were no sufficiently bright quasars accessible for this project. Instead, the astronomers calibrated on the emission from water masers present in a relatively nearby region, and they verified the stability of the masers' properties by a second level of checks against hot dust around a bright reference star. With these reliable measurements the team was able to measure the total mass of the gas and dust in the source -- about sixty solar-masses worth, or just about enough to bind the two objects together gravitationally. The results not only help to identify the birth of a possible, massive twin, but also illustrate the success of innovative techniques that are developed to capitalize on as new astronomical instruments used to peer into the heavens.

Exoplanet around Gamma Cephei

The star Gamma Cephei is about thirty-eight light-years from Earth, readily visible in the sky roughly between Polaris (the North Star) and the "chair" in Cassiopeia. Astronomer's have suspected for nearly twenty years that Gamma Cep had a planetary companion. In fact, Gamma Cep was one of the first stars to be be studied with new instruments capable of measuring the slight wobble in the star's motion that signals the presence of an orbiting companion. Today the field of extra-solar planetology is booming, with over 200 confirmed examples, and every example helps scientists studying the Earth's formation and evolution to refine their models. Gamma Cep, however, remains one of the pioneering discoveries of the field.

The story of scientific progress can often make for dramatic reading, and the case of Gamma Cep is a good example. After discovering what appeared to be wobbles in the star's orbit, astronomers began to monitor the star very closely. After a few years they reported that they had been in error. They decided that tiny spectral variations they observed, corresponding to a stellar wobble of only about ninety kilometers per hour (for comparison, the Earth's velocity around the Sun is about 100,000 kilometer per hour) were instead due to periodic flaring activity in the star's photosphere. To cap it off, the astronomers concluded that Gamma Cep was in a binary system, with a companion star orbiting every 30 years or so -- the companion's period and stellar type were very poorly known -- potentially disrupting the orbits of any planets (if there were any). Not everyone was convinced about the retraction, however, and astronomers have continued to try to refine the observations to sort out this puzzle.

SAO astronomer Guillermo Torres, writing in last month's Astrophysical Journal, finally presents a convincing case. By using data from the Hipparcos astrometry satellite, and reviewing many of the ground-based observations as well, he finds that indeed Gamma Cep does have a planetary companion. The planet has a mass of at least 1.4 Jupiter-masses (but less than ten times this amount), and it orbits the star at approximately the distance that Mars orbits our Sun. The companion star, he calculates, is a dwarf star of mass about 0.4 solar-masses, and it orbits the star only ten times further away than the planet; it is the closest companion known for any planet-hosting star. The companion is so faint and so close to Gamma Cep that it has never been directly seen, and it is itself of great interest to astronomers who wonder how such a small, nearby companion can long survive ... and how its gravity might disrupt the path of planets orbiting closer to the primary star. The new paper is a fine example of how careful research can resolve a long-standing mystery while simultaneously offering a peek into more subtle puzzles.

Exoplanet Atmosphere

The hundreds of currently identified extrasolar planets (that is, planets around stars other than our Sun) have known masses and orbits, but they are otherwise rather mysterious objects. For example, although all of them are massive enough to have their own atmospheres, almost nothing is known about these atmospheres. The reason is simple: only a few of these planets have been directly detected at all due to the very bright glare of their nearby stars. Nearly all of them were discovered indirectly from the wobbling motions of their parent stars. Studying a planetary atmosphere is therefore a formidable task, but one which is of tremendous interest to people trying to determine how the Earth's atmosphere formed and evolved.

CfA astronomer David Charbonneau and seven of his colleagues have now succeeded in studying the atmosphere of the planet around the nearby star known as HD189733. The planet, a bit more massive than Jupiter, orbits very close to its star - only 3% of the distance of the Earth from Sun, and so much closer to its star than Mercury is from the Sun. Every 2.2 days the planet completes an orbit that takes it across the face of the star as seen from the Earth (a "transit"). Knowing the orbital parameters very precisely, the astronomers used the Spitzer Space Telescope spectrometer to stare at the star just when the planet was at the center of its transit, and they repeated the observations a month later.

In the infrared this planet shines with about one-half of one percent as much light as does its star -- not much, but enough for modern instruments. Using sophisticated data analysis techniques to insure they were really looking at the planet's light and not at extraneous scattered signal, the scientists obtained an infrared spectrum of the planet at the wavelength where they had expected to see the telltale signature of atmospheric water vapor. But, to their surprise, none was seen, nor was there any indication of methane gas, another atmospheric constituent they had anticipated from theoretical models. It is still too soon to determine the implications of these unexpected results, and whether they imply, for example, that the models of extrasolar planetary atmospheres are more generally in error. The new result, however, emphasizes the dramatic, even astonishing ability of scientists on Earth to study the chemistry of the atmospheres of exotic planets around distant stars.

Oxygen in Space

Oxygen is obviously one of the gases we care most about here on Earth, and so it is not surprising that astronomers have been trying for over fifty years to determine its abundance in the cosmos. Oxygen not only lets us breathe, it is a key chemical constituent in space, combining with many other elements like carbon to form molecules like CO (carbon monoxide) that help to control the temperatures of prestellar, molecular clouds through a variety of thermodynamic processes. What is surprising is that astronomer still cannot find much of the oxygen in space. If the amount of oxygen we see on Earth (relative to other elements) is representative of its cosmic abundance, and scientists think that it is, then huge amounts of oxygen are hiding somewhere in space.

SAO astronomer Gary Melnick is part of a team of eight astronomers that used the Spitzer Space Telescope to search for one particularly promising reservoir for "unseen" oxygen: solid grains of carbon dioxide (CO_2) ice. The scientists observed eight stars buried deep within cold gas and dust in the interstellar medium in the constellation of Taurus. They discovered the absorption signature of CO_2 ice in all of these sources, and by careful modeling of the strength of that signature they determined that about one-quarter of all of the oxygen in space is neither in the form of atomic nor molecular gas, but is bound up in CO_2 ice. They also note that an additional 30% or so of the oxygen is found in interstellar dust particles (silicates for example). So, according to these astronomers, more than half of cosmic oxygen is trapped in solids of one type or another, with another 10% as carbon monoxide (CO) gas. That still leaves about 35% of the expected oxygen unaccounted for, but the scientists suggest ways in which future research can prospect for this most beneficial of gases.

Cygnus Loop Supernova Remnant

When a supernova explodes, its blast sweeps up surrounding gas with a powerful shock wave. A typical supernova shock has more energy in the motions of its material than the Sun will emit in its lifetime. As the shock wave moves outward, the shocked gas that is swept up forms a shell that glows as brightly as a million Suns. Virtually all of the elements essential to life were created in stars or in supernovae, not at time of the big bang; they were dispersed by these supernova remnants (SNRs) into space, where they became available to make new stars and planets. Astronomers are keenly interested in studying the glowing shells of SNRs to determine their chemical composition and properties.

A significant fraction of the elements in space collect in the form of dust grains. Silicon and carbon, especially, coagulate into silicate (i.e., sand) or graphite grains, and these grains in turn act to collect other chemicals on their surfaces. As the SNR shock wave moves outward, it heats and disrupts these dust grains, and ionizes some of the the ejected material. A team of three SAO astronomers, John Raymond, Terrance Gaetz, and Andrew Szentgyorgyi, together with three colleagues, has used the Far Ultraviolet Spectroscopic Explorer satellite to probe the light emitted by the hot gas in one famous SNR, the "Cygnus Loop" nebula. The scientists discovered a set of characteristic atomic features that were never before seen in a SNR. Arising from iron, silicon, and other elements that had been known from other emission features, the new features result from million-degree gas in the shock.

In a typical interstellar medium perhaps 40%-90% of the silicon is locked up in these dust grains. The astronomers calculate from their data that at least 50% of this silicon is liberated from the grains by the shock, thus making it available for other chemical reactions in the interstellar medium. The new research also tracked changes in the state of the ionized gas across the remnant material, and determined the oxygen abundance of the emitting gas. The results also refine our knowledge of many other details of SNRs, shock densities and structure for example, and hence our understanding of the key process in which chemical elements are dispersed into space, perhaps to find their way into future planets. Reference: "Far UV Spectroscopic Explorer spectroscopy of the XA region in the Cygnus Loop Supernova Remnant," R. Sankrit et al., Astronomical Journal, 133, 1383, 2007.

Quasar: Giant Jet

Quasars are galaxies with massive black holes at their cores around which vast amounts of energy are being radiated -- quasars are among the most powerful energy sources known. Streaming out from the center of about 10% of quasars, like cosmic laser beams, are powerful jets of electrons and other subatomic particles that travel at nearly the speed of light. Quasars are mysterious. No one knows for sure how they form, how they develop in time, or how their stupendous energies are produced. Because they are so bright, quasars can be seen even when they are very far away, and this combination of being both highly energetic and located at cosmological distances makes quasars interesting to astronomers who are trying to better understand both the nature of black holes (our own Galaxy has one at its center) and the conditions in the early universe that prompt these monsters to form.

The jets streaming from the regions around black holes typically emit in a wide range of wavelengths, including X-ray wavelengths. SAO astronomers Aneta Siemiginowska and Daniel Harris, along with five colleagues, used the Chandra X-ray Observatory to study one of the longest known X-ray jets. Stretching across about one million light-years -- far longer than the diameter of the Milky Way galaxy -- the jet comes from the center of a quasar so distant that its light has been traveling towards us for 8.2 billion years, almost two-thirds of the age of the universe. The team finds that the jet looks sharply different at X-ray wavelengths than it does at radio wavelengths. From their analysis, the astronomers conclude that the simple models previously suggested for jets do not work: the X-rays appear to arise from the jet proper, while radio emission comes from a different region, a surrounding jet "sheath." Furthermore, there is evidence for intermittent jet activity that produces knots and other structures. The new results not only help to understand what is going on in this dramatic case, they also suggest that similar processes may in fact be at work in many quasar jets.

Globular Cluster: Core

Globular clusters are roughly spherical ensembles of stars, as many as a million stars in some cases, that are gravitationally bound together in groups whose diameters can be as small as only tens of light-years. For comparison, the closest star to our Sun is about four light-years away. Globular clusters are typically located in the outer regions of galaxies. The Milky Way galaxy has about 200 globular clusters orbiting it. The stars in globular clusters are highly concentrated towards the centers, where they swarm around in complex motions determined by gravity. Globular clusters are interesting in their own right as being home to some of the oldest known stars. They also help astronomers decipher how galaxies evolve because collisions between galaxies appear to be relatively commonplace, and globular clusters participate in those interactions from sensitive locations in the galaxies' halos. Globular clusters provide an important laboratory for studies of stellar evolution because their rich isolated population of stars are all about the same age. And not least, because of their very high density of stars, globular clusters are key places to study how stars interact with each other.

Messier 30 is a globular cluster in the Milky Way, and is one of only about twenty-one globular clusters that show evidence for extraordinarily high densities at its core -- perhaps hundreds of thousands of solar masses in a volume about a light-year on a side, one of the highest density environments in the galaxy. In such a crowded space, stars are expected to interact with each other frequently. CfA astronomers Jonathan Grindlay and Peter Edmonds, together with three colleagues, have combined new Chandra X-ray Observatory data with optical images from the Hubble Space Telescope and ground-based facilities to discover and study three stars only a few tenths of a light-year from the central core, and another six only about one and one-half light-years from the core.

The astronomers find that one of these sources is actually a binary in which one of the two stars is a neutron star: the small, compact object remaining after a certain type of massive star explodes as a supernova. Made up predominantly of neutrons, neutron stars are about a hundred trillion times more dense than water. Models of globular clusters suggest that as stars whiz past each other in the crowded central regions they occasionally join into a binary. The newly discovered binary may be just such a couple. The results, besides providing remarkable new information on the innermost parts of a globular cluster's core, also help to confirm and extend models of how stars interact with one another, and with their environments.

Brown Dward Twins

The small star with the long name of 2MASS-J1207334-393254 is about 179 light-years from Earth. It has a mass of only about twenty-four Jupiters, too little to be able to ignite hydrogen burning in its core. It is what astronomers call a brown dwarf star, a star that burns dimly by the power of deuterium fusion. Astronomers interested in how stars like the Sun and planets like the Earth formed and evolved are naturally interested in brown dwarfs because these objects bridge the gap in mass between stars and planets. But 2MASS-J1207334-393254 is interesting for another reason as well: it has a companion, an even smaller, eight-Jupiter-mass-size body orbiting it, and furthermore it appears that both objects have protostellar disks surrounding them as they orbit each other.

Scientists over the past few years have concluded that the companion in this binary does not fit the expected behavior of brown dwarf stars. In particular, its inferred temperature is entirely inconsistent with its luminosity - at least as far as the models can determine. SAO astronomers Subhanjoy Mohanty and Eric Mamajek, together with two colleagues, have obtained new data that resolve these and some other discrepancies as well. From sensitive new optical observations and careful modeling, they conclude that the companion is actually surrounded by a disk of material that is seen nearly edge-on; the total mass of that disk is about the same as the mass of our Moon. The primary star also has a disk of material, making this object a binary system with two disks. The astronomers hypothesize that these conclusions, if correct, suggest that about eight million years ago both stars formed together from a large disk of material that was perhaps as much as ten times more massive than it is now. If even brown dwarf stars can have disks this large, then they might also have asteroids or other even smaller bodies in their midst. The new results help to resolve most of the inconsistencies that had been worrying astronomers, and help to illustrate the rich complexity of stellar development in the cosmic cycle of stellar birth.

Exoplanet: Water

An "exoplanet" is an extra-solar planet -- a planet orbiting a star other than our own Sun. Over 120 exoplanets have been discovered in the past decade in a scientific revolution that has been led to a very significant degree by SAO. Astronomers trying to identify the key processes involved in the formation of the Earth look to these extra-solar examples to test their models and refine their understanding of our home.

CfA astronomer (and past CfA student) David Charbonneau, together with seven of his colleagues, has used the Spitzer Space Telescope to obtain an infrared spectrum of the the planet orbiting the nearby star (63 light-years distant) HD 189733. This star has a Jupiter-sized planet orbiting very close by, at only 3.1% of the distance of the Earth from the Sun, and so much closer than even Mercury from our Sun. As as result of its proximity to the star, this exoplanet's atmosphere is thought to be quite hot, more than about 1000 kelvin, making it easier to see in the infrared than most other known exoplanets. Easier maybe...but certainly not easy. The infrared light from this exoplanet is still only about 0.5% of the flux from its parent star. Using meticulous data acquisition and analysis techniques, however, the team was able to extract the light of the planet from starlight.

To their surprise the astronomers did not see any evidence for the atmospheric molecules that virtually all the models had predicted: water, and methane. In fact, the spectrum of the atmosphere showed no molecular features at all. The reason for the absence of water is a mystery. Indeed, the scientists point out that simply reducing the quantity of water predicted to be in the atmosphere will not solve the problem because then the models predict other characteristics that are not observed. The intriguing result needs confirmation, and the team plans to repeat their measurements, but it also suggests that there is a fundamental gap in our understanding of the formation of planetary atmospheres around exoplanets.

Black Hole Neighborhood

Astronomers have come to realize that black holes are fairly common in the universe. Massive black holes -- ones that contain millions or even billions of solar masses of material -- are thought to reside at the centers (nuclei) of most galaxies, including our own Milky Way. These stupendous objects help to determine the behavior of galaxies through their powerful gravitational force and so are of fundamental importance, yet astronomers do not understand their nature, how they develop, or how they affect the subsequent evolution of a galaxy and its stars.

Active galactic nuclei (AGN) have massive black holes which are vigorously accreting material in a process that typically results in the ejection of jets of particles, and the stimulation of the environment to radiate brightly at many wavelengths, most notably in the X-ray and the infrared. SAO astronomers Guido Risaliti, Martin Elvis, Pepi Fabbiano, Alessandro Baldi, and Andreas Zezas, together with a colleague, report using the Chandra X-ray Observatory to study one such AGN that was known to vary in X-ray brightness on a timescale of weeks. Because such rapid variations are difficult to explain via changes in the X-ray emitting gas, the scientists argue instead that the variability is produced by occultation of the AGN by intervening clouds of gas and dust that move into or out of our line-of-sight to the X-ray emitting region. Writing in the Astrophysical Journal Letters, the team reports that careful monitoring and analysis of the variable X-ray light shows that the emission originates in a region whose size is remarkably small -- corresponding roughly to less than the diameter of our solar system proper, i.e., twice the distance of Pluto from our Sun. Furthermore, they calculate from their measurements that the obscuring cloud itself lies only about a hundred times farther away from the X-ray emitting region, possibly as part of a circumnuclear torus of material. If so, this torus is much more compact than had been previously imagined, and may also play a role in feeding the accretion process. The new results provide some of the first direct measurements of the environments of these exotic, supermassive black holes.

White Dwarf Star: Lowest Mass

When a star like our Sun gets very old, after another seven billion years or so, it will no longer be able to burn its nuclear fuel. With only about half of the its mass remaining, it will shrink to a fraction of its radius and become a white dwarf star. White dwarfs are common, the most famous one being the companion to the brightest star in the sky, Sirius. But although they are common, and although they represent the final stage of our own Sun, astronomers still do not understand their full range of character, or the parameters that determine what they become. One reason is that many white dwarfs are, like the companion of Sirius, located in binary systems that are likely to influence the details of how they age.

SAO astronomer Warren Brown and three of his colleagues announced this week that they have discovered the lowest mass white dwarf known: a Saturn-sized ball of helium containing only about one-fifth the mass of the Sun. The new-found object lies about 7,400 light-years from Earth near the border of the constellations Lynx and Ursa Major. Although small in terms of mass, it is about nine times larger in dimensions than a typical white dwarf star.

Using SAO's MMT telescope at the Fred L. Whipple Observatory in Arizona, the astronomers conducted a survey of forty-two candidate low mass white dwarfs. From a meticulous analysis of their data, the team identified one candidate as being the lowest mass white dwarf known. The scientists predicted the reason why this white dwarf has so little mass: it has an unseen companion (probably another white dwarf) that has sucked away much of its material. Finally, the team measured a telltale wobble in the movement of the white dwarf that demonstrated this prediction was correct. The results not only shed light on the geriatric community which our Sun will someday join, they also help to explain certain other astronomical phenomena, like pulsars; these objects also seem to have low mass white dwarfs as companions.

Luminous Infrared Galaxies

Our Milky Way home galaxy, like most galaxies, shines brightly in visible light because its stars are hot and emit at optical wavelengths. But twenty years ago the Infrared Astronomy Satellite, IRAS, discovered that the universe contained many fabulously luminous galaxies -- some more than a thousand times brighter than our galaxy -- that are practically invisible at optical wavelengths. The reason is that their infrared light comes not from stars, but from dust that is heated by starlight (although only up to frosty temperatures of about 70 kelvin, about 200 degrees below zero Celsius). At these temperatures very little optical light is emitted, while the dust absorbs most of the visible stellar radiation. IRAS galaxies are luminous because they contain so much of this dust. Astronomers are quite sure that the energy to heat the dust to even these temperatures comes from giant bursts of star formation that are hidden from optical view by the dust itself, but they do not know what triggers these bursts, nor whether our Milky Way might someday erupt in a similar way.

Two mechanisms have been suggested for triggering massive starbursts in a galaxy: collisions with another galaxy, and/or processes associated with a massive black hole at the galaxy's center. Most luminous infrared galaxies are so far away, however, that telescopes have been unable to sort out which of these two mechanisms is correct, or more precisely, when one mechanism predominates over the other. Five CfA astronomers, Sukanya Chakrabarti, Thomas Cox, Lars Hernquist, Philip Hopkins, and Brant Robertson, and a colleague, have performed detailed computer simulations of interacting galaxies using a code that they developed over several years. In a new paper out this month, they use their results to calculate the luminosity of these interacting systems, to uncover how that luminosity evolves with time as a galaxy ages, and to determine the relative contributions of starburst activity and nuclear activity to the infrared emission.

Their comprehensive calculations offer persuasive answers to several key problems. They find, contrary to previous thinking, that the most critical element in determining the temperature and luminosity of a galaxy is not the illumination from the source (either a starburst or the nucleus). Instead, it is injection of winds or jets into the galaxy, or other disruptive activity from the starburst or nucleus, that is responsible because this feedback stimulates the gas in the galaxy to produce more stars. They also find that the black hole nucleus produces warmer dust because it tends to deposit its energy in a much shorter time frame (only tens of millions of years versus hundreds of millions of years for starbursts). The new results not only shed important light on these cosmic beacons, they point to continued productive use of computer simulations in the study of how galaxies are born and age.