Introduction
The Universe is home to numerous exotic and beautiful phenomena, some of which can generate almost inconceivable amounts of energy.
Supermassive black holes, merging neutron stars, streams of hot gas moving close to the speed of light ... these are but a few of the marvels that generate gamma-ray radiation, the most energetic form of radiation, billions of times more energetic than the type of light visible to our eyes.
What is happening to produce this much energy? What happens to the surrounding environment near these phenomena? How will studying these energetic objects add to our understanding of the very nature of the Universe and how it behaves?
![The GLAST instrument after arriving at Cape Canaveral in May 2008.]()
The GLAST instrument after arriving at Cape Canaveral in May 2008.
The Fermi Gamma-ray Space Telescope, formerly GLAST, will open this high-energy world to exploration and help us to answer these questions.
With Fermi, astronomers will at long last have a superior tool to study how black holes, notorious for pulling matter in, can accelerate jets of gas outward at fantastic speeds. Physicists will be able to study subatomic particles at energies far greater than those seen in ground-based particle accelerators. And cosmologists will gain valuable information about the birth and early evolution of the Universe.
For this unique endeavor, one that brings together the astrophysics and particle physics communities, NASA is collaborating with the U.S. Department of Energy and science communities and institutions in France, Germany, Japan, Italy and Sweden. General Dynamics was chosen to build the spacecraft. Fermi was launched June 11, 2008.
Mission Objectives Overview
- Explore the most extreme environments in the Universe, where nature harnesses energies far beyond anything possible on Earth.
- Search for signs of new laws of physics and what composes the mysterious Dark Matter.
- Explain how black holes accelerate immense jets of material to nearly light speed.
- Help crack the mysteries of the stupendously powerful explosions known as gamma-ray bursts.
- Answer long-standing questions across a broad range of topics, including solar flares, pulsars and the origin of cosmic rays.
The Mission
The Fermi Gamma-Ray Space Telescope is the latest high energy gamma-ray observatory launched by NASA. It is designed to study energetic phenomena from a variety of celestial sources.
Key Scientific Objectives of Fermi
- Understand how particles are accelerated in pulsars, supernovae, and active galaxies.
- Identify currently unidentified gamma-ray sources in the sky.
- Determine the high energy behavior of gamma-ray bursts.
- Study phenomena which may shed light on dark matter and particle physics.
While under development, the satellite was known as the Gamma-ray Large Area Space Telescope (GLAST).
With the release of its first-light image of the gamma-ray sky, NASA renamed the satellite to honor Enrico Fermi.
Instruments
Fermi uses two instruments to observe the gamma-ray Universe:
- the Large Area Telescope and
- the Gamma-ray Burst Monitor.
Large Area Telescope (LAT)
The primary instrument on Fermi is the Large Area Telescope, or LAT, built at Stanford University. It has a wide field-of-view, allowing it to see about 20% of the sky at the same time. It will detect gamma rays with energies ranging from 20 MeV to 300 GeV (10 million to 150 billion times the energy of the light detected by the human eye). With the resolution and sensitivity of its imaging capabilities, the LAT represents a major advancement over previous gamma-ray telescopes.
The LAT detects gamma rays by using a technique known as pair-conversion. When a gamma ray slams into a layer of tungsten in the detector, it creates an electron and positron pair.
cutaway of the Fermi LAT instrument
These particles in turn hit another, deeper layer of tungsten, each creating further particles and so on. The direction of the incoming gamma ray is determined by tracking the direction of these cascading particles back to their source using high-precision silicon detectors. Furthermore, a separate detector counts up the total energy of all the particles created. Since the total energy of the particles created depends on the energy of the original gamma ray, counting up the total energy determines the energy of that gamma ray. In this way, Fermi is able to make gamma-ray images of astronomical objects, while also determining the energy for each detected gamma ray.
A cut-away of the Fermi LAT instrument.
A gamma-ray enters at the top of the stack, and electron-positron pairs form within the stack. The LAT has 16 such stacks.
Gamma-ray Burst Monitor (GBM)
![Fermi Gamma-ray Burst Monitor]()
Fermi Gamma-ray Burst Monitor
The secondary instrument onboard is the Gamma-ray Burst Monitor, or GBM, built by Marshall Space Flight Center and the Max-Planck-Institut for extraterrestrische Physik in Germany. The GBM is designed to observe gamma ray bursts (GRBs), which are sudden, brief flashes of gamma rays that occur about once a day at random positions in the sky. While NASA's Swift satellite has been studying gamma-ray bursts since 2004, there is still much to learn about them. Fermi is adding to our knowledge by studying GRBs to a much higher energy than Swift. The GBM has such a large field-of-view that it will be able to see bursts from over 2/3 of the sky at one time, providing locations for follow-up observations of these enigmatic explosions. The GBM is composed of two sets of detectors - 12 sodium iodide (NaI) scintillators and two cylindrical bismuth germanate (BGO) detectors. When gamma rays interact with these crystalline detectors, they produce flashes of visible light, which the detector can use to locate the gamma-ray burst on the sky. The GBM works at a lower energy range than the LAT, so together they provide the widest range of energy detection in the gamma-ray regime for any satellite ever built.
Observing Plan
Since the LAT can see 20% of the sky at any time and can cover the sky every three hours, the primary observing objective of Fermi is to conduct a detailed survey of the entire sky. Fermi is devoting its first year to conducting this survey,and will release this data to astronomers all around the world. Fermi will then begin a program of observations which will be proposed by astronomers.
During its first year, Fermi is also observing gamma-ray bursts, and using the LAT to study bursts in detail. This will continue throughout the mission.
Science Areas that Fermi will Study
Fermi will study not only a wide array of objects, but also attempt to solve some fundamental unsolved issues.
The EGRET gamma-ray sources.
Unidentified Objects – Plot of the location of the EGRET sources in the sky.
Note the number (and locations) of the unidentified sources (green circles).
In the 1990s, the EGRET instrument aboard the Compton Gamma-Ray Observatory observed 271 gamma-ray sources. Interestingly, two-thirds of them have not been identified because their positions in the sky were not known precisely enough. That is, we don't know whether these gamma-rays objects are stars or black holes or neutron stars or supernovae or distant galaxies. Astronomers expect many of them could be in other galaxies. The LAT on Fermi will observe thousands of sources (including the ones seen by EGRET), and will be able to pinpoint their locations well enough so other telescopes can look at them. These observations should help to identify these objects. Some may be pulsars or supernova remnants in our galaxy, while others may be in other galaxies. And some may hold suprises!
Looking for Dark Matter
Fermi will also look for annihilations of postulated weakly-interacting massive particles (WIMPs) in the halo of the Milky Way, and around other galaxies. These particles could possibly be the dark matter, which so far makes its presence known only by its gravitational pull on matter that we can see. Recent theoretical work suggests that annihilation of WIMPs could be detectable with Fermi. The signature would be spatially diffuse, narrow line emission peaked toward the Galactic center, and around other galaxies. It would not be detected as a point source, but from an area possibly as large as the full moon. In addition, the gamma-ray light would be continuous, not short like a gamma-ray burst.
(Source: NASA's Imagine the Universe - "Satellite Showcase: Fermi Gamma-Ray Space Telescope.")
Observatory Launched 2008
WASHINGTON — NASA's newest observatory, the Gamma-ray Large Area Space Telescope, or GLAST, has begun its mission of exploring the universe in high-energy gamma rays. The spacecraft and its revolutionary instruments passed their orbital checkout with flying colors. NASA announced August 2008 that GLAST has been renamed the Fermi Gamma-ray Space Telescope.
The new name honors Prof. Enrico Fermi (1901 - 1954), a pioneer in high-energy physics.
Logo credit for the Fermi Gamma-ray Space Telescope – NASA/Sonoma State University/Aurore Simonnet.
Other Fermi Science Topics
(from the Fermi web site)
Logo for Fermi Gamma ray Space Telescope
Click link below right for more information on the Fermi Gamma-ray Space Telescope »
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Introduction
The Universe is home to numerous exotic and beautiful phenomena, some of which can generate almost inconceivable amounts of energy.
Supermassive black holes, merging neutron stars, streams of hot gas moving close to the speed of light ... these are but a few of the marvels that generate gamma-ray radiation, the most energetic form of radiation, billions of times more energetic than the type of light visible to our eyes.
What is happening to produce this much energy? What happens to the surrounding environment near these phenomena? How will studying these energetic objects add to our understanding of the very nature of the Universe and how it behaves?
![The GLAST instrument after arriving at Cape Canaveral in May 2008.]()
The GLAST instrument after arriving at Cape Canaveral in May 2008.
The Fermi Gamma-ray Space Telescope, formerly GLAST, will open this high-energy world to exploration and help us to answer these questions.
With Fermi, astronomers will at long last have a superior tool to study how black holes, notorious for pulling matter in, can accelerate jets of gas outward at fantastic speeds. Physicists will be able to study subatomic particles at energies far greater than those seen in ground-based particle accelerators. And cosmologists will gain valuable information about the birth and early evolution of the Universe.
For this unique endeavor, one that brings together the astrophysics and particle physics communities, NASA is collaborating with the U.S. Department of Energy and science communities and institutions in France, Germany, Japan, Italy and Sweden. General Dynamics was chosen to build the spacecraft. Fermi was launched June 11, 2008.
Mission Objectives Overview
- Explore the most extreme environments in the Universe, where nature harnesses energies far beyond anything possible on Earth.
- Search for signs of new laws of physics and what composes the mysterious Dark Matter.
- Explain how black holes accelerate immense jets of material to nearly light speed.
- Help crack the mysteries of the stupendously powerful explosions known as gamma-ray bursts.
- Answer long-standing questions across a broad range of topics, including solar flares, pulsars and the origin of cosmic rays.
The Mission
The Fermi Gamma-Ray Space Telescope is the latest high energy gamma-ray observatory launched by NASA. It is designed to study energetic phenomena from a variety of celestial sources.
Key Scientific Objectives of Fermi
- Understand how particles are accelerated in pulsars, supernovae, and active galaxies.
- Identify currently unidentified gamma-ray sources in the sky.
- Determine the high energy behavior of gamma-ray bursts.
- Study phenomena which may shed light on dark matter and particle physics.
While under development, the satellite was known as the Gamma-ray Large Area Space Telescope (GLAST).
With the release of its first-light image of the gamma-ray sky, NASA renamed the satellite to honor Enrico Fermi.
Instruments
Fermi uses two instruments to observe the gamma-ray Universe:
- the Large Area Telescope and
- the Gamma-ray Burst Monitor.
Large Area Telescope (LAT)
The primary instrument on Fermi is the Large Area Telescope, or LAT, built at Stanford University. It has a wide field-of-view, allowing it to see about 20% of the sky at the same time. It will detect gamma rays with energies ranging from 20 MeV to 300 GeV (10 million to 150 billion times the energy of the light detected by the human eye). With the resolution and sensitivity of its imaging capabilities, the LAT represents a major advancement over previous gamma-ray telescopes.
The LAT detects gamma rays by using a technique known as pair-conversion. When a gamma ray slams into a layer of tungsten in the detector, it creates an electron and positron pair.
cutaway of the Fermi LAT instrument
These particles in turn hit another, deeper layer of tungsten, each creating further particles and so on. The direction of the incoming gamma ray is determined by tracking the direction of these cascading particles back to their source using high-precision silicon detectors. Furthermore, a separate detector counts up the total energy of all the particles created. Since the total energy of the particles created depends on the energy of the original gamma ray, counting up the total energy determines the energy of that gamma ray. In this way, Fermi is able to make gamma-ray images of astronomical objects, while also determining the energy for each detected gamma ray.
A cut-away of the Fermi LAT instrument.
A gamma-ray enters at the top of the stack, and electron-positron pairs form within the stack. The LAT has 16 such stacks.
Gamma-ray Burst Monitor (GBM)
![Fermi Gamma-ray Burst Monitor]()
Fermi Gamma-ray Burst Monitor
The secondary instrument onboard is the Gamma-ray Burst Monitor, or GBM, built by Marshall Space Flight Center and the Max-Planck-Institut for extraterrestrische Physik in Germany. The GBM is designed to observe gamma ray bursts (GRBs), which are sudden, brief flashes of gamma rays that occur about once a day at random positions in the sky. While NASA's Swift satellite has been studying gamma-ray bursts since 2004, there is still much to learn about them. Fermi is adding to our knowledge by studying GRBs to a much higher energy than Swift. The GBM has such a large field-of-view that it will be able to see bursts from over 2/3 of the sky at one time, providing locations for follow-up observations of these enigmatic explosions. The GBM is composed of two sets of detectors - 12 sodium iodide (NaI) scintillators and two cylindrical bismuth germanate (BGO) detectors. When gamma rays interact with these crystalline detectors, they produce flashes of visible light, which the detector can use to locate the gamma-ray burst on the sky. The GBM works at a lower energy range than the LAT, so together they provide the widest range of energy detection in the gamma-ray regime for any satellite ever built.
Observing Plan
Since the LAT can see 20% of the sky at any time and can cover the sky every three hours, the primary observing objective of Fermi is to conduct a detailed survey of the entire sky. Fermi is devoting its first year to conducting this survey,and will release this data to astronomers all around the world. Fermi will then begin a program of observations which will be proposed by astronomers.
During its first year, Fermi is also observing gamma-ray bursts, and using the LAT to study bursts in detail. This will continue throughout the mission.
Science Areas that Fermi will Study
Fermi will study not only a wide array of objects, but also attempt to solve some fundamental unsolved issues.
The EGRET gamma-ray sources.
Unidentified Objects – Plot of the location of the EGRET sources in the sky.
Note the number (and locations) of the unidentified sources (green circles).
In the 1990s, the EGRET instrument aboard the Compton Gamma-Ray Observatory observed 271 gamma-ray sources. Interestingly, two-thirds of them have not been identified because their positions in the sky were not known precisely enough. That is, we don't know whether these gamma-rays objects are stars or black holes or neutron stars or supernovae or distant galaxies. Astronomers expect many of them could be in other galaxies. The LAT on Fermi will observe thousands of sources (including the ones seen by EGRET), and will be able to pinpoint their locations well enough so other telescopes can look at them. These observations should help to identify these objects. Some may be pulsars or supernova remnants in our galaxy, while others may be in other galaxies. And some may hold suprises!
Looking for Dark Matter
Fermi will also look for annihilations of postulated weakly-interacting massive particles (WIMPs) in the halo of the Milky Way, and around other galaxies. These particles could possibly be the dark matter, which so far makes its presence known only by its gravitational pull on matter that we can see. Recent theoretical work suggests that annihilation of WIMPs could be detectable with Fermi. The signature would be spatially diffuse, narrow line emission peaked toward the Galactic center, and around other galaxies. It would not be detected as a point source, but from an area possibly as large as the full moon. In addition, the gamma-ray light would be continuous, not short like a gamma-ray burst.
(Source: NASA's Imagine the Universe - "Satellite Showcase: Fermi Gamma-Ray Space Telescope.")
Observatory Launched 2008
WASHINGTON — NASA's newest observatory, the Gamma-ray Large Area Space Telescope, or GLAST, has begun its mission of exploring the universe in high-energy gamma rays. The spacecraft and its revolutionary instruments passed their orbital checkout with flying colors. NASA announced August 2008 that GLAST has been renamed the Fermi Gamma-ray Space Telescope.
The new name honors Prof. Enrico Fermi (1901 - 1954), a pioneer in high-energy physics.
Logo credit for the Fermi Gamma-ray Space Telescope – NASA/Sonoma State University/Aurore Simonnet.
Other Fermi Science Topics
(from the Fermi web site)
Logo for Fermi Gamma ray Space Telescope
Click link below right for more information on the Fermi Gamma-ray Space Telescope »
Are you absolutely sure you want to delete this article? This process cannot be undone and is permanent.
Yes, Delete This Article
Are you absolutely sure you want to remove this article? This process cannot be undone and is permanent.
Yes, Remove This Article
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