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Cosmic Explosions
MARCH 2007
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By Ron Cowen
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Massive stars die in the biggest explosions since the big bang. Now scientists are deciphering the stories of these doomed suns.
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Ever since he was a teenager, Stan Woosley has had a love for chemical elements and a fondness for blowing things up. Growing up in the late 1950s in Texas, "I did everything you could do with potassium nitrate, perchlorate, and permanganate, mixed with a lot of other things," he says. "If you mixed potassium nitrate with sulfur and charcoal, you got gunpowder. If you mixed it with sugar, you got a lot of smoke and a nice pink fire." He tested his explosive concoctions on a Fort Worth golf course: "I screwed the jar down tight and ran like hell."
Woosley, now an astronomer at the University of California at Santa Cruz, has graduated to bigger explosions—much bigger. Woosley studies some of the most powerful explosions since the birth of the universe: supernovas, the violent deaths of stars.
The universe twinkles with these cataclysms. They happen every second or so, usually in some unimaginably remote galaxy, blazing as bright as hundreds of billions of stars and creating a fireball that expands and cools for months.
We're lucky that they rarely strike close to home. The last supernova in our own galaxy exploded in 1604, rivaling Jupiter's brightness in the night sky and deeply impressing Johannes Kepler, the pioneering astronomer. A nearby supernova—within a few light-years—would bathe the Earth in lethal radiation.
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.
Subscribe to National Geographic magazine.
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