The Farthest Gamma-Ray Burst

Scientists running the Interplanetary Network--a cluster of spacecraft from the U.S. and Europe patrolling the skies--described yesterday at a conference in Rome the farthest gamma-ray burst ever observed. (These bursts are fairly frequent, as the animation at right shows.) The stunningly powerful explosion occurred on January 31 this year in the southern constellation of Carina some 11 billion light-years away. The scientists believe that the burst, christened GRB 000131, emanated from the death of an enormous star more than 30 times as massive as the sun. That event, they say, most likely took place when the universe was only one tenth its current age.

"Although this distant burst was observed on January 31, 2000, it has taken scientists eight months to study its source," says Kevin Hurley, a physicist at the University of California, Berkeley, who runs the Interplanetary Network of probes. "The flash of high-energy gamma radiation appeared at first to be relatively normal. It was neither very faint, which might indicate that it had traveled a long way from its source, nor very bright, which would hint at a somewhat closer origin." The fact that this burst was the farthest on record became apparent only when Finnish and Danish astronomers witnessed its source through the European Southern Observatory's Very Large Telescope in Chile. The exceedingly dim afterglow they saw indicated that GRB 000131 was indeed coming from a great distance.

Hurley and his colleagues suggest that perhaps they only glimpsed such a far-off event because it flashed a sharply focused beam of gamma-ray radiation--like a headlight in the dark--right at them. "If this were the Olympics, we'd have the gold medal now," Hurley says. "Still, the fact that such a faint, distant source can produce a burst of gamma rays that appears to be of more or less average intensity from Earth hasn't been explained yet."