Astronomers have detected one more clue to the origins of gamma-ray bursts, those highly energetic explosions that occur in distant galaxies. The gas cloud radiating from the source of one burst carried with it the telltale by-products of a supernova explosion. The finding, published today in Nature, strengthens the tie between supernovae and gamma-ray bursts and suggests that a burst occurs just a few days after a supernova.
There are currently two leading theories regarding the formation of gamma-ray bursts. The first posits that they result from the collapse of an extremely massive star to a black hole, which prompts a supernova (see image)--an explosion that ejects a spherical fireball of material. The second holds that the bursts are formed by a neutron star falling into a black hole. To further investigate the origins of these phenomena, James N. Reeves of the University of Leicester and colleagues studied the x-ray spectrum of the burst known as GRB011211. The Beppo-SAX satellite located the event, which lasted for 270 seconds, on December 11, 2001. Eleven hours after the burst, the XMM-Newton telescope began observing GRB011211's so-called afterglow.
The telescope detected a mixture of elements in the afterglow, including magnesium, silicon, sulfur, argon and calcium racing away from the source of the burst at a speed one tenth of the speed of light. Such elements are typical of a supernova. The researchers report that the supernova probably occurred between 10 to 100 hours before the gamma-ray burst. "Our understanding of gamma-ray bursts becomes clearer with the new observations," writes Herman L. Marshall of the Massachusetts Institute of Technology in an accompanying commentary. He notes, however, that "there is evidently a great deal yet to be discovered about [gamma-ray bursts]."