For first time, astronomers witness a star explode and die

WASHINGTON — For the first time, astronomers have witnessed the death throes of a massive star as it was blowing up in a violent explosion called a supernova.

The remnants of thousands of supernovae have been seen before, but only days or weeks after they occurred. Now, thanks to a lucky break, they've witnessed the birth of a supernova while it was happening.

The star-burst lasted only five minutes, but it shone brighter than a billion normal stars combined, according to a paper to be published in Thursday's edition of the journal Nature.

This type of supernova occurs when a star burns up its nuclear fuel and collapses under its own weight, compresses and explodes, shattering it to smithereens. The cataclysm flings out elements like oxygen, iron and calcium that are necessary to make planets like Earth.

This event began at 9:33 a.m. (EST) on Jan. 9 of this year. Astronomers using NASA's Swift X-ray satellite were studying an older supernova in a galaxy named NGC 2770, when they spotted a brilliant flash of light nearby.

They realized it was probably a supernova and immediately alerted astronomers around the world. Other telescopes in space and on the ground, using ultraviolet light, X-rays and radio waves, confirmed the finding.

"We were in the right place, at the right time, with the right telescopes, and witnessed history," said Alicia Soderberg, an astronomer at Princeton University in Princeton, N.J., and lead author of the Nature paper.

"For years we have dreamed of seeing a star just as it was exploding, but actually finding one is a once-in-a-lifetime event," said Soderberg, leader of the Swift team that observed the event.

The new supernova has been named SN 2008D. It's 90 million light years away in the constellation Lynx. A light year is about 5.9 trillion miles.

Its parent star was about the same size as our sun but 30 times heavier, according to Maryam Modjaz, an astronomer at the University of California at Berkeley, co-author of a separate paper submitted to the Astrophysical Journal.

After the star exploded, its outer layers were ejected at velocities up to 70 percent of the speed of light, said Peter Meszaros, an astrophysicist at Penn State University in University Park, Pa., and a member of the Swift team.

"The death of a massive star marks the birth of its explosion, along with the creation and ejection of heavy elements like oxygen and calcium necessary for life as we know it," said Alex Filippenko, a Berkeley astronomy professor who discovered one of the first supernovae of this type in 1985.

"It was a gift of nature for Swift to be observing that patch of sky when the supernova exploded," said Neil Gehrels, Swift's chief scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

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