GAMMA RAY BURSTS

Until recently, little had been known about the "fireballs" known as gamma ray bursts. Since their discovery about 30 years ago by defense satellites, these intense cosmic outbursts seem to occur randomly around the sky about once per day.

In 1997, a team of astronomers using a pair of NSF radio telescopes made the first measurements of the size and expansion of gamma ray bursts. These scientists have learned the fireball is actually debris that expands at very nearly the speed of light. In these events enormous amounts of energy are released within a very small region which is considered much less than the typical distance separating stars.

The cause of gamma ray bursts is still unknown. One burst in 1997 lasted for only 15 seconds, but emitted an afterglow that lasted for several days. Study of the afterglow reveals the initial explosion released more energy during 15 seconds than the sun will release in its entire 10-billion year lifetime, making it one of the most energetic events known to have occurred since the Big Bang.

Optical studies reveal the 1997 gamma ray burst was at least seven billion light-years away. Because of their short duration, gamma ray bursts are difficult to "catch." Astronomers are devising clever techniques in order to learn the cause, frequency and role these events play in the evolution of the universe.