For decades scientists have struggled to explain the origins of gamma-ray bursts, huge blasts of energy that occur daily in far-off galaxies. Now it appears they may have an answer. The results of two studies of recent gamma-ray bursts, published today in the journal Science, indicate that exploding stars called supernovae may spawn some of these blasts.
The teams studied x-ray spectra, which are emitted by the bursts, using the Chandra X-Ray Observatory and the BeppoSAX satellite. Examinations of these spectra revealed characteristic "fingerprints" indicating that, in each case, as the burst expanded it passed through a dense, iron-rich cloud of gas. That cloud, the researchers say, probably resulted from a supernova explosion. As a star evolves it produces increasingly heavy elements, and by the time it reaches supernova status, the star is producing iron, the heaviest element possible for it to make.
Initial estimates from the spectra data seemed to indicate that the supernova spat out the cloud just before the gamma-ray burst. According to calculations of cloud density, however, the teams estimate a 10-year lag between the supernova explosion and the burst. They thus propose what they have dubbed the "supranova" model, in which a burst results not directly from a supernova explosion but from the delayed collapse of a neutron star created by the supernova. "We cannot rule out other scenarios yet," remarks Filippo Frontera of the University of Ferrara, one of the lead authors, "but this one is the simplest, and the most consistent with our results."