A long time ago, in a galaxy far, far away, a giant star exploded in a supernova so enormous and violent that it blew itself entirely out of existence. At a news briefing at NASA headquarters in Washington, D.C., today, astronomers told stunning tales of Supernova 2006gy, the largest such event ever recorded and one so extreme it existed only in theory up to now. They also linked the event to a similar display that could be cooking right in Earth's own neighborhood of the Milky Way.
Up to now, all known supernovae have begun in one of two ways. First, if a star grows massive enough, its nuclear fires can no longer overcome the crushing force of its gravity, in which case it runs out of fuel and collapses. The collapse creates so much heat and pressure that the star forges the heaviest elements known and blasts them and most of its outer layers back out into space, along with blinding radiation. Second, when a sunlike star has ripped off enough material from a nearby binary companion, it likewise collapses and explodes. In both cases, depending on the initial mass and temperature of the exploding star, the supernova will create either a tiny but extremely dense object called a neutron star or an infinitesimal but even more massive object known as a black hole.
SN 2006gy is something else entirely. Astronomers using both space-based and ground-based telescopes, including the Chandra X-Ray Observatory, have analyzed the destruction of the giant star, located in the galaxy NGC 1260 about 240 million light-years away. The original star is estimated to have been at least 100 times heavier than the sun, placing it in an extremely rare weight class. The team has discovered that the explosion was at least 100 times more luminous than any previously observed supernova. "It really is different from anything we've seen before," said team leader Nathan Smith of the University of California, Berkeley, at the news briefing. "It's freakishly massive."
Smith said the event seems to be the first observation of a phenomenon called a pair-instability supernova. According to theory, the enormous accumulated mass of the star ignites a special type of reaction that creates both electrons and their antimatter counterparts, called positrons. These particles annihilate one another with so much energy that when the supernova begins, they eject the star's constituent elements entirely, with no neutron star or black hole left behind. "In this type of supernova," Smith said, "you're taking 20 times the mass of the sun and blowing it out into space."
The discovery is "extremely important in terms of understanding the evolution of the most massive stars," says x-ray astronomer Michael Corcoran of NASA's Goddard Space Flight Center in Greenbelt, Maryland. The results are particularly important, he says, because astronomers are watching a star of similar mass within the Milky Way. That star, called Eta Carinae, could explode like SN 2006gy, which "probably wouldn't be good for Earth," Corcoran says, because the event could destroy communications satellites and damage the planet's healing ozone layer.
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