Compton Gamma-ray Observatory
CGRO
NASA
Launch Year: 1991
Agency: NASA
For more information: http://cossc.gsfc.nasa.gov/
Compared to Explorer XI's weight of roughly 82 pounds, CGRO was a behemoth
at 17 tons, making it the largest astrophysical payload of its time. Gamma-ray
instruments comprised almost half of the satellite's bulk. By using these larger
telescopes, CGRO could gather more gamma-ray photons than previous satellites.
The instruments studied photon energies ranging from 20,000 electron volts (20
keV) to more than 30 billion electron volts (30 GeV). CGRO's productive career
lasted until 2000, when NASA directed the satellite into Earth's atmosphere.
Before its death, CGRO showed us that our universe is a violent and rapidly
changing place with its detection of gamma rays, identification of gamma-ray
bursts, and the discovery of a new class of quasars. A number of European countries
in association with the ESA contributed to this mission's success.
Initially, Gamma-rays appeared to come primarily from the Milky Way galaxy.
Generalized Gamma-ray emission from the galaxy would be produced by cosmic ray
interactions with the dust and gas in the galactic plane. Some pulsars and supernova
remnants were also identified as Gamma-ray sources. The Compton Gamma-ray Observatory
(CGRO) discovered point sources of Gamma-rays outside the plane of the galaxy.
These sources were identified with a special type of active galaxy now known
as blazars. CGRO ultimately detected several dozen blazars associated with faint
optical sources. It is also now realized that there is a uniform background
Gamma-ray emission from the entire sky. At the present time (2004) the source
of this emission is unknown.
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