Even more importantly, the new satellite will relay very accurate positions of the bursts within one or two minutes of initial detection. In a few months NASA will launch a gamma-ray detecting satellite known as Swift, which is expected to localize about 100 gamma-ray bursts each year. The mystery we need to confront at this point, Kulkarni adds, is why the energy in some explosions chooses a different escape route than in others.Īt any rate, adds Dale Frail, an astronomer at the VLA and coauthor of the Nature manuscript, astrophysicists will almost certainly make progress in the near future. "By relying on gamma rays or X rays to tell us when an explosion is taking place, we may be exposing only the tip of the cosmic explosion iceberg." This means that cosmic explosions are beasts with different faces but the same body."Īccording to Shri Kulkarni, MacArthur Professor of Astronomy and Planetary Science at Caltech and Berger's thesis supervisor, these findings are significant because they suggest that many more explosions may go undetected. "In all cases we found that the total energy of the explosion is the same. "The insight gained from the burst of March 29 prompted us to examine previously studied cosmic explosions," says Berger. X-ray flashes were thought to occupy the middle ground. On the other hand, the more numerous supernovae of type Ic in our local part of the universe seem to be weaker explosions that produce only slow particles. Until now it was generally assumed that the explosions are so titanic that the accelerated particles rushing out in antipodal jets always give off prodigious amounts of gamma radiation, sometimes for hundreds of seconds. Gamma-ray bursts, first detected accidentally decades ago by military satellites watching for nuclear tests on Earth and in space, occur about once a day. "This stumped me," Berger adds, "because gamma-ray bursts are supposed to produce mainly gamma rays, not radio waves!" "By monitoring all the escape routes, we realized that the gamma rays were just a small part of the story for this burst," Berger says, referring to the nested jet of the burst of March 29, which had a thin core of weak gamma rays surrounded by a slow and massive envelope that produced copious radio waves.
The burst, which at 2.6 billion light-years is the closest classical gamma-ray burst ever detected, allowed Berger and the other team members to obtain unprecedented detail about the jets shooting out from the dying star. This insight was made possible by radio observations, carried out at the National Radio Astronomy Observatory's Very Large Array (VLA), and Caltech's Owens Valley Radio Observatory, of a gamma-ray burst that was localized by NASA's High Energy Transient Explorer (HETE) satellite on March 29 of this year. In the November 13 issue of the journal Nature, Caltech graduate student Edo Berger and an international group of colleagues report that cosmic explosions have pretty much the same total energy, but this energy is divided up differently between fast and slow jets in each explosion. The main difference between them is the "escape route" used by the energy as it flees from the dying star and its newly born black hole. A new study this week demonstrates that all three flavors of these cosmic explosions-gamma-ray bursts, X-ray flashes, and certain supernovae of type Ic-are in fact connected by their common explosive energy, suggesting that a single type of phenomenon, the explosion of a massive star, is the culprit. PASADENA, Calif.-For the past several decades, astrophysicists have been puzzling over the origin of powerful but seemingly different explosions that light up the cosmos several times a day.