These infrared images of GRB 050724 and its host galaxy were taken with the Carnegie Observatories’ Magellan telescopes. The red color of the elliptical host galaxy shows that no new stars have been forming for several billion years, implicating old neutron stars, or a neutron star and a black hole, as the source of short gamma-ray bursts (Image courtesy Edo Berger / Carnegie Observatories)
Cosmic gamma-ray bursts, the most powerful explosions in the universe, have the extreme brilliance of a billion billion Suns and occur several times a day. But they are not all created equal. For several decades astronomers have known that two types exist--long ones that last for tens or hundreds of seconds, and short bursts, which last a few milliseconds to a second. Intense research over the last decade has shown that long bursts are the death throes of massive stars in distant, young, and vigorously star forming galaxies. The origin of the short gamma-ray bursts, however, has been shrouded in mystery until now. Edo Berger, a Hubble post-doctoral fellow at the Carnegie Observatories, is lead author of the first study that accurately pinpoints a short gamma-ray burst to an old dead galaxy, implicating a population of old neutron stars as the sources of these explosions. The study appears in the December 15, 2005, issue of Nature.
"We had no idea if they explode in nearby galaxies, or the farthest reaches of the universe, or even what kind of object was producing them," stated Berger. "Now, after eluding us for years, we have finally found out what objects are giving rise to these explosions." he added.
Because short gamma-ray bursts are fainter than the long bursts, they have been very difficult to localize until recently, with the advent of NASA’s Swift satellite and rapid follow-up by telescopes on the ground. Swift detects and observes gamma-ray bursts in multiple wavelengths and alerts astronomers who quickly point ground-based telescopes to catch the fading afterglow--the dying ember that glows for hours or days after the burst of gamma-rays.
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