Astronomers think they may have finally resolved the mystery of the most powerful explosion ever detected in the universe. On March 26, 1998, a European satellite recorded a flash of gamma rays estimated to rival the big bang in energy. The eruption, astronomers now say, was probably generated during the abrupt and violent transition between the death of a massive star and the resulting birth of a black hole.
Since 1967, astronomers have observed and studied brilliant flashes of gamma radiation in the sky. These gamma-ray bursts have been seen all over the sky at seemingly random times. No one knew what caused them, or if they were a part of the local universe or lay at cosmological distances.
Recently, with the help of the Italian-Dutch satellite BeppoSAX, astronomers for the first time were able to determine that the bursts originate in remote galaxies. Given the brightness of the bursts and their great distance, astronomers concluded that gamma-ray bursts are the most powerful in the universe.
In a paper appearing in this week's science journal Nature, an international team led by astronomers from the California Institute of Technology present evidence that the March 1998 gamma ray burst, known as GRB 980326, was associated with a supernova explosion in a remote galaxy. If confirmed, it would be the first direct evidence for a mechanism that produces gamma-ray bursts.
Whether supernovae or neutron stars are involved, black holes are thought to be at the bottom of the gamma-ray phenomenon.
Two theoretical scenarios describe how a gamma-ray burst might be produced. In one scenario, two neutron stars or black holes collide, generating the burst and leaving in its place a single massive black hole.
In the second scenario, the catastrophic explosion of a massive star creates a black hole. As the black hole collapses, concentrated jets of intense radiation are sent beaming out of the black hole's polar axis. If the axis is not pointed toward Earth, we see a supernova. If it is, however, we see a gamma-ray burst and a supernova.
The search for the source of the GRB 980326 burst was carried out at the W. M. Keck Observatory's 10-meter telescope located atop Mauna Kea, Hawaii. The team not only found a visible gamma-ray afterglow, they also detected a never-before-seen rebrightening at optical wavelengths of an apparent host galaxy located at the position of the gamma-ray burst. Eight months later, the galaxy vanished entirely, which was also unprecedented. Nevertheless, the unexpected rebrightening and subsequent fading of the source corresponds to the behavior of a supernova, from its initial brilliance to its gradual diminution in brightness. Spectra taken of the object at different times also reinforce this theory.
Joshua S. Bloom, a graduate student at Caltech and lead author of the paper says, "This appears to be the smoking gun for the origin of some gamma-ray bursts, a perfect marriage of the two brightest events in the universe. It is wonderful to be a part of such a discovery."
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