VII.

Gamma-Ray Telescopes

Gamma rays are electromagnetic radiation with wavelengths even shorter than X rays. Some of the most catastrophic events in the universe, such as neutron star collisions and black holes, blast high-energy gamma rays across space. Since gamma rays cannot penetrate Earth’s atmosphere, they must be observed from space. In the early 1990s the Compton Gamma Ray Observatory (GRO) found that mysterious gamma-ray bursts are evenly distributed across the sky. Because of their even distribution, astronomers believe that these bursts are extraordinarily powerful events that occur in normal galaxies. Many astronomers believe collisions between two neutron stars or between a neutron star and a black hole produce these bursts.

Gamma-ray telescopes consist of two or more gamma-ray detectors in a line. A detector is triggered by any gamma ray that passes through it, no matter what direction the gamma ray is traveling. To observe gamma rays from a particular source, then, at least two detectors are placed in a line pointing to the source. Only a gamma ray from the targeted source will pass through both detectors.