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Yet the legacy of supernovas is as close as our own bodies. The carbon in our cells, the oxygen in the air, the silicon in rocks and computer chips, the iron in our blood and our machines—just about every atom heavier than hydrogen and helium—was forged inside ancient stars and strewn across the universe when they exploded billions of years ago. Eager to understand our origins and, in some cases, simply wild about things that go bang, astronomers have been struggling for decades to understand why stars that shine peacefully for millions of years suddenly blow up.

Lately they've had two big breaks. One is a revelation about potent blasts of high-energy gamma rays that come from distant points in the heavens. For decades astronomers have puzzled over their origins, but space probes recently clinched the answer, which Woosley proposed more than a decade ago: Many gamma-ray bursts are the early warning signals from supernovas, emitted minutes before the explosion.

The link offers a glimpse of events leading up to the actual explosion—another mystery. There, too, researchers have made headway. Looking not at the heavens but at computer models of supernovas, some think they have figured out what may trigger the final cataclysm. The missing element may be unimaginably powerful reverberations—the sound of a star singing its own swan song.

For astronomers, there's usually no rush to study something before it vanishes. "The universe usually evolves as slowly as watching paint dry," says one. But these days, hundreds of astronomers keep cell phones and beepers close by so they can rush to work like doctors on call. They're waiting for word from a spacecraft called Swift.

Swift, launched in 2004, scans the skies for gamma rays. When it detects a burst, it swivels its telescopes toward the source to get a good fix and detect the afterglow—the lingering point of light that marks the spot where a burst originated. It also sends an alert to earthbound astronomers, who can take a closer look with bigger telescopes.

Early on February 18, 2006, Swift recorded an outpouring of gamma rays from somewhere toward the constellation Aries. Within three minutes, the satellite had determined the position of the burst and broadcast an alert. Two days later, astronomers at a telescope in Arizona reported that the burst came from a small, nearby galaxy, only a fraction as far away as usual.

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