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Huge Explosion Reveals the Most Massive Star Known

All supernova explosions are violent affairs, but this onetakes the cake. Astronomers have spotted a new type of extremely bright cosmicexplosion they think originates from an exceptionally massive star.

This breed of explosion has been long predicted, but neverbefore seen. Like allsupernovas, the blast is thought to have marked the endof a star's life. But in this case, that star may have started out with 200times the mass of the sun.

The supernova in question, SN2007bi, was observed in 2007 ina nearby dwarf galaxy. Scientists knew at once it was somethingdifferent because it was about 50 to 100 times brighter than a typicalsupernova.

"It was much brighter, and it was bright for a verylong time," said researcher Paolo Mazzali of the Max-Planck Institute forAstrophysics in Germany. "We could observe this thing almost two yearsafter it was discovered, where you normally don?t see anything anymore."

After analyzing its signature, astronomers published a paperin the Dec. 3 issue of the journal Nature confirming that it matchestheoretical predictions of a so-called pair-instability supernova.

"There were some doubts that they existed," saidastronomer Norbert Langer of the University of Bonn in Germany, who did notwork on the project. Langer wrote an opinion essay on the finding in the sameissue of Nature. "There were severe doubts that stars that massive couldever form in the universe. Now we seem to be very sure that there was a starwith 200 solar masses."

In a pair-instability supernova, the star has neared the endof its life and exhausted its main supplies of hydrogen and helium, leaving ita core of mostly oxygen. In smallerstars, the core continues to burn until eventually it is all iron, thencollapses in a Type II supernova, leaving behind a remnant black hole orneutron star.

But in the case of an extremely massive star, while its coreis still made of oxygen, it releases photons that are so energetic, they createpairs of electrons and their anti-matter opposites, positrons. When the matterand antimatter meet, they annihilate each other. This reaction reduces thestar's pressure, and it collapses, igniting the oxygen core in a runawaynuclear explosion that eats up the whole star, leaving no remnant at all.

The discovery of this rare type of supernova suggests that afew stars actually can grow into such large behemoths ? which has long been atopic of debate.

"I was never a believer in very massive stars,"Mazzali told SPACE.com. "Seeing something like this explode means thesethings exist. This is a fairly new development in the formation of stars."

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