Gamma-Ray All-Sky Survey
Gamma-Ray All-Sky Survey
| Group Name | mwGamma |
| Reference | Compton Gamma-Ray Observatory |
| Prepared by | Brian Abbott (AMNH/Hayden) |
| Labels | No |
| Files | mw-gamray.speck |
| Dependencies | 08-gamma-512.sgi |
| Wavelength | 4.17e-15 m |
| Frequency | > 7.2 x 1013 GHz |
Gamma-ray light is the highest energy radiation in the electromagnetic spectrum. Gamma-rays have very short wavelengths and high frequencies and it can penetrate solid objects. Radioactive decay of atoms produce high-energy particles, such as alpha, beta, and gamma particles. An alpha particle is a positively-charged helium nucleus. It is the least energetic radioactive particle and is stopped by a sheet of paper or the skin. Beta particles are similar to electrons and can travel in air for a few feet before losing their energy. They are shielded by aluminum or glass and penetrate only a fraction of an inch in our skin. Gamma particles are the most energetic, requiring several inches of lead or concrete for protection from burns, cancer, and genetic mutations.
Because our atmosphere shields us from cosmic gamma-ray light, gamma-ray astronomy did not develop until we were able to place balloons or satellites above the atmosphere. The first gamma-ray space telescope was carried aboard the Explorer XI satellite in 1961. Subsequent missions detected gamma-rays in the Galaxy and in the Universe. Gamma-rays are produced in massive explosions and high-speed collisions, suggesting the Universe is more violent than astronomers once thought.
A breakthrough came in the late 1960s and early 1970s when the United States placed a series of satellites in orbit to detect gamma-rays from nuclear explosions. They detected flashes of bright gamma-ray radiation, but these were coming from space. In April 1991, NASA's Compton Gamma-Ray Observatory (CGRO) was launched into space by the Space Shuttle Atlantis. Before being de-orbited in June 2000, the telescope discovered gamma-ray bursts, cataloged gamma-ray sources, and surveyed the sky.
This all-sky survey is from the Energetic Gamma-Ray Experiment Telescope (EGRET) on the CGRO. The rainbow-colored map indicates gamma-ray bright areas (white, red) and dimmer areas (blue, indigo). The brightness along the Galactic plane is due to gamma-rays interacting with interstellar gas. Several bright sources appear as white spots on the map. These include the Crab, Geminga, and Vela pulsars in the Galactic plane. The brightest source above the plane, 3C 279, is a quasar that lies about 4 billion light-years away.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott