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Oversize supernova

Although they can't fully explain why a star blows up, astronomers thought that they had accurately determined the maximum mass that a star could have before exploding as a common type of supernova. Now, they've found a star that breaks the rule.

According to prevailing theory, a type 1a supernova is triggered by a compact star called a white dwarf piling up matter stolen from a bloated companion star. When the white dwarf becomes as heavy as 1.4 times the mass of the sun, the high density and heat generated by the matter spark a thermonuclear explosion.

Researchers have found a type 1a supernova so luminous that it must have been produced by a much heavier star than the standard theory allows. Andy Howell of the University of Toronto and his colleagues report in the Sept. 21 Nature that the supernova, called SNLS-03D3bb, is 2.2 times as bright as expected and that the star that exploded had to be 50 percent heavier than the 1.4-solar-mass limit.

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