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GAMMA-RAY BURSTS: THE LIGHT FANTASTIC

The most titanic explosions in the universe take the form of gamma-ray bursts. These bright bursts of energy appear from random regions in space and typically last a few seconds. United States Air Force Vela satellites first discovered them in the 1960s. Since then, numerous theories of their origins have been proposed, but the causes of gamma-ray bursts remain unknown.

NASA's Hubble Space Telescope has helped astronomers trace these bursts back to distant galaxies. The principal limitation in understanding the bursts was the difficulty in pinpointing their direction in the sky. Unlike visible light, gamma rays are exceedingly difficult to observe with a telescope, and the burst's short duration exacerbates the problem.

Hubble has teamed up with several observatories, including X-ray satellites, to collect information on bursts. Among the most energetic was the gamma-ray burst labeled GRB971214, detected Dec. 14, 1997. Astronomers measured the distance to a faint galaxy from which the burst originated. Using the Italian/Dutch satellite BeppoSAX, astronomers pinpointed the direction of the burst, which permitted follow-up observations with the world's most powerful telescopes. These follow-up observations tracked the burst's "afterglow" in radio waves and X-ray, visible, and infrared light. While gamma-ray bursts last only a few seconds, their afterglows can be studied for several months. By analyzing these afterglows, astronomers have discovered that the bursts do not originate within our own galaxy, the Milky Way, but rather are associated with extremely distant galaxies.

The Hubble telescope images of GRB971214 confirmed the association of the burst's afterglow with a faint galaxy.

Astronomers still don't understand the origins of bursts. Theories suggest they happen where vigorous star formation takes place. Gamma-ray bursts may be created by the mergers of a pair of neutron stars or black holes or a hypernova, a theorized type of exceptionally violent exploding star.


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