Four space-based detectors have picked up what might be a statistical fluke--or a vital clue in what Bonnard Teegarden of NASA's Goddard Space Flight Center in Greenbelt, Maryland, calls "the biggest puzzle in modern astronomy." Teegarden is a member of a U.S.-Russian team that announced this week that over the space of 2 days in October, the detectors picked up four gamma-ray bursts from the same small patch of sky. Gamma-ray bursts are short-lived blasts of energy for which astronomers have no explanation, because no burst has ever been correlated with any visible sources. And until now, no burst has ever been seen to repeat itself.
The new observation, reported on the Internet, may give astronomers their first break in the gamma-ray mystery. Astronomers are fairly certain that the first two spikes, on 27 October, represent two distinct bursts. But the two spikes that appeared 2 days later were just 23 minutes apart. "We are convinced those two...are one real long burst," says Charles Meegan of NASA's Marshall Space Flight Center in Huntsville, Alabama. And all of the bursts, he and his colleagues think, came from the same source.
A repeating gamma-ray burst would allow astronomers to eliminate some of the rival explanations for these events. One popular theory, for instance, holds that gamma-ray bursts are caused by coalescing neutron stars, an idea that would be ruled out by repeated bursts. "It could not make something that would burst again 2 days later," says Meegan.
Another possibility is that the triple burst is simply a statistical coincidence. "It seems to be unlikely to be due to chance, although we still need to work real hard to make sure that's the case," Meegan says. The bottom line, however, is that astronomers still have no idea what the source of the bursts is. Says Meegan, "It makes the enigma of gamma-ray bursts even stranger than we thought."