Sun: Middle Age
Sun: Middle Age
| Topics: |  Stellar Evolution Stars Sun |
Introduction
Once our sun began to produce energy in its core by fusing hydrogen into helium, it embarked on a long 'middle age' . As the nuclear fires became more efficient, the infant sun began to expand very slowly. At first the sun only shone with 70% of its modern brightness. But as it continued to evolve over eons of time, its brightness grew by 7% every billion years. When trilobites first crawled on shallow ocean bottoms 500 million years ago, the sun was much fainter in the sky than it is today. Earth would have been in a deep-freeze had it not been for the warming actions of an atmosphere laced with trace gases like water and carbon dioxide.
Our sun today as it appears in the light of hydrogen-alpha.(Courtesy: Institute for Astrophysics, Gottingen.)
Our sun has already spent 4.5 billion years as a star, and will continue to shine normally for at least another 6 billion years as a middle-aged star before becoming a red giant.
4.0 billion years ago
According to standard models of stellar evolution, 4 billion years ago the sun was about 25% cooler than it is today, and terrestrial and Martian temperatures were below freezing. Because the faint, young sun could not have melted ice into liquid water until about 1 billion years ago, Earth should have been lifeless for billions of years. But geological evidence shows that there was plenty of liquid water as far back as about 4 billion years ago. One alternative model for solar evolution, with a brighter, slightly more massive, younger sun, invokes mass loss (5%-10%) through a declining solar wind. But Gaidos et al. [501] use results of deep radio observations of a nearby 0.3 billion-year-old solar-mass star, selected on the basis of its analogy to the early Sun, and find that the early solar wind for this young Sun would not produce enough mass loss as required by the alternative model [Gaidos et al, 2000].
3.5 billion years ago
Based on studies of stellar activity and rotation, stars like the sun will continue to spin slower as the age. By 1 billion years after formation, the suns rotation period will probably have dropped from once per day, to about once per 15 days. 3 billion years ago. Solar luminosity is 20 % less than today. 2 billion years ago. Solar luminosity is 15 % less than today. 1 billion years ago. Solar luminosity is 10 % less than today.
References
- "The Faint Young Sun Paradox: An Observational Test of an Alternative Solar Model" Gaidos, E. J.; Güdel, M.; Blake, G. A, 2000. University of Washington, Space Physics and Aeronomy in Geophysical Research Letters - Volume 27, Issue 4, Paper Number 2000GL010740,
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Preview Image
"Orion Nebula, M42, NGC 1976" - This dramatic image offers a peek inside a cavern of roiling dust and gas where thousands of stars are forming. The image, taken between 2004 and 2005 by the Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope, represents the sharpest view ever taken of this region, called the Orion Nebula. More than 3,000 stars of various sizes appear in this image. Some of them have never been seen in visible light. These stars reside in a dramatic dust-and-gas landscape of plateaus, mountains, and valleys that are reminiscent of the Grand Canyon.
The Orion Nebula is a picture book of star formation, from the massive, young stars that are shaping the nebula to the pillars of dense gas that may be the homes of budding stars. The bright central region is the home of the four heftiest stars in the nebula. The stars are called the Trapezium because they are arranged in a trapezoid pattern. Ultraviolet light unleashed by these stars is carving a cavity in the nebula and disrupting the growth of hundreds of smaller stars. Located near the Trapezium stars are stars still young enough to have disks of material encircling them. These disks are called protoplanetary disks or "proplyds" and are too small to see clearly in this image. The disks are the building blocks of solar systems.
The bright glow at upper left is from M43, a small region being shaped by a massive, young star's ultraviolet light. Astronomers call the region a miniature Orion Nebula because only one star is sculpting the landscape. The Orion Nebula has four such stars. Next to M43 are dense, dark pillars of dust and gas that point toward the Trapezium. These pillars are resisting erosion from the Trapezium's intense ultraviolet light. The glowing region on the right reveals arcs and bubbles formed when stellar winds - streams of charged particles ejected from the Trapezium stars — collide with material.
The faint red stars near the bottom are the myriad brown dwarfs that Hubble spied for the first time in the nebula in visible light. Sometimes called "failed stars," brown dwarfs are cool objects that are too small to be ordinary stars because they cannot sustain nuclear fusion in their cores the way our Sun does. The dark red column, below, left, shows an illuminated edge of the cavity wall.
The Orion Nebula is 1,500 light-years away, the nearest star-forming region to Earth. Astronomers used 520 Hubble images, taken in five colors, to make this picture. They also added ground-based photos to fill out the nebula. The ACS mosaic covers approximately the apparent angular size of the full moon. View full-size image. (Source: NASA,ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team.)
Citation
Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Sun: Middle Age." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published November 26, 2007].
<http://www.cosmosportal.org/articles/view/138658/>
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