By early 2000, astronomers had made considerable progress in understanding one of the universe's most puzzling phenomena: gamma-ray bursts. These intense flashes of radiation, which come from all points of the sky, are the most powerful emissions of energy in the universe since the big bang, the explosive event that most astronomers believe gave birth to the universe. For 30 years, researchers using instruments on satellites and powerful ground-based telescopes had scanned the skies for the sources of gamma-ray bursts in a vain attempt to explain them. Finally, in the 1990's, the mysterious bursts began to give up their secrets.
Gamma ray bursts (GRB's) appear without warning about once a day from random directions in the heavens. Gamma rays are the highest-energy form of light in the electromagnetic spectrum, the range of electromagnetic waves that includes visible light as well as ultraviolet rays, X rays, infrared rays, and radio waves. Earth's atmosphere blocks gamma rays from reaching the ground. However, they can be detected by satellites in space that orbit above Earth's atmosphere.
GRB's were discovered in 1967 by United States Vela satellites, which had been launched to monitor global compliance with the nuclear test-ban treaty. By early 2000, astronomers had recorded more than 2,500 such bursts.