Most big old stars at the end of their lives tend to go out in a fairly mundane way - either exploding with incredible violence as supernovae, or collapsing into ultradense universe-warping unfeasiblo-gunge as a black hole.

But now astronomers say they have seen evidence of a long-hypothesised third path for a large star; that of brewing up huge amounts of antimatter within one's own guts and blowing up with such outrageous force as to make a supernova seem like a beetle farting.

The star in question is known as "Y-155", which blinked very dimly into visibility just over two years ago in the constellation Cetus and was spotted by the Blanco telescope in Chile. According to astronomer Peter Garnavich, Y-155's death throes are unimpressive from here, but that's only because it lies no less than seven billion lightyears away.

“In our images, Y-155 appeared a million times fainter than the unaided human eye can detect, but that is because of its enormous distance,” says the stargazing prof. “If Y-155 had exploded in the Milky Way [our home galaxy] it would have knocked our socks off.”

Y-155 was discovered as part of the international astroboffinry alliance known as "Equation of State: SupErNovae trace Cosmic Expansion", or ESSENCE. Garnavich is a member of the ESSENCE team, and announced the Earth-shattering (had it been near enough) hypernova spotting at a conference in Washington DC yesterday.

“ESSENCE found many explosions in our six years of searching, but Y-155 stood out as the most powerful and unusual of all our discoveries,” says Garnavich.

The possibility that stars 150 to 300 times the mass of our Sun might expire as antimatter-driven hypernovae rather than dull black holes or regular supernovae was calculated more than 40 years back, but only recently has it even been possible to observe them. It's thought that such unusual, galaxy-shaking blasts can occur only in "pristine" regions of space where the ur-hydrogen of the universe has not been much contaminated with heavy elements by earlier generations of stars. ®