Saturday, October 8, 2016
Gamma Ray Astronomy International Gamma Ray Astrophysics Laboratory
Gamma Ray Astronomy International Gamma Ray Astrophysics Laboratory
Gamma-Ray Astronomy, field of astronomy involving the observation of gamma rays from outer space. A gamma ray is a very-high-energy form of electromagnetic radiation with a wavelength even shorter than that of an X ray. Gamma rays are produced by changes in atomic nuclei and are also decay products of collisions between cosmic rays and interstellar matter. Their study aids in understanding the high-energy processes Although highly energetic, most gamma rays are absorbed by Earth’s atmosphere. Gamma-ray astronomy did not really begin until the space age provided satellite-borne detecting devices (see Satellite, Artificial). In 1991 NASA launched the 17-ton Compton Gamma Ray Observatory (GRO) into orbit high above Earth. GRO’s observations added a quasar, called 3C279, to the list of known gamma-ray sources, which also include the pulsar in the Crab Nebula and the binary star system Cygnus X-3.
Within only a few months of operation, GRO’s four telescopes had already detected over 100 gamma-ray bursters, brief bursts of energy at gamma-ray wavelengths. The origin of these bursts was unknown. The GRO was unable to pinpoint the location of a burst, so astronomers did not even know whether the bursters originated in Earth’s galaxy or in distant galaxies. In 1996 the Italian Space Agency launched an Italian-Dutch gamma-ray and X-ray space telescope called BeppoSAX into orbit around Earth. BeppoSAX was able to locate the origin of gamma-ray bursts in the sky. In 1997 American astronomers using the Palomar Observatory on Mount Palomar near San Diego, California, and the Keck II telescope on Mauna Kea in Hawaii discovered an afterglow of visual light in a spot that BeppoSAX had found a gamma-ray burst. By studying the way that the light from the object had changed as it traveled to Earth, the astronomers were able to estimate the distance to the object. They concluded that the burst occurred about 12 billion light-years, more than half of the size of the observable universe, from Earth.
In 1998 astronomers studying data from the initial BeppoSAX observation and the afterglow of the burst concluded that, for a few seconds, the burst was brighter than the rest of the entire observable universe. This brightness means the event was more energetic than any other known event besides the big bang, the explosion at the very beginning of the universe. Since 1998 astronomers have matched the locations of several gamma-ray bursts with explosions of massive stars called supernovas.
In 2002 the European Space Agency and Russia launched the International Gamma-Ray Astrophysics Laboratory (INTEGRAL). INTEGRAL can better discriminate between different gamma-ray wavelengths and can more finely determine the locations of gamma-ray sources than previous satellites. X-ray and visible light detectors will allow INTEGRAL to observe gamma-ray sources simultaneously at a range of different wavelengths.
occurring in outer space, such as those associated with neutron stars, quasars, and black holes. Because positrons (antimatter electrons) produce gamma rays when they are annihilated, gamma-ray astronomy also serves as a means of measuring the presence of antimatter. See also Astronomy.
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