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> Record-busting supernova prompts new ideas on death of stars -
NGC 1260 (Persei):
about one-fifth of the way from Algol to Nu Persei,
at 28 Taurus 15.
Mark A. Holmes
Record-busting supernova prompts new ideas on death of stars
Wed Nov 14, 2:33 PM ET
PARIS (AFP) - Astronomers analysing the brightest supernova ever
detected say the titanic flare has reshaped thinking about the death
struggle of gigantic stars.
Supernova SN2006gy, located 240 million light years away in galaxy NGC
1260, entered the record books in September last year when it
dramatically brewed into an explosion 50 billion times brighter than
It was about 100 times brighter than the flash of a typical supernova,
as a dying star is called.
Poring over this extraordinary event, US stargazers said on Wednesday
that the SN 2006gy was probably caused by a truly enormous star, a
behemoth at least 100 times more massive than the Sun.
And, they theorise, the star did not blow up just once -- but several
"We usually think of a supernova as the death of a star, but in this
case the same star can blow up half a dozen times," said Stan Woosley
of the University of California at Santa Cruz, who led the study
published in the journal Nature.
Woosley's hypothetical model starts with what happens when an
exceptionally big star -- something 90-130 solar masses -- nears the
end of its life.
The temperature in the stellar core gets so hot that some of the
star's gamma radiation converts into electrons and their anti-matter
counterparts, called positrons.
The conversion causes the blast of radiation to suddenly fall, and the
star begins to shrink.
"As the core contracts it goes deeper into instability until it
collapses and begins to burn fuel explosively," Woosley said.
"The star then expands violently, but not enough to disrupt the whole
star. For stars between 90 and 130 solar masses you get pulses.
"It hits this instability, violently expands, then radiates and
contracts until it gets hotter and hits the instability again. It
keeps going until it loses enough mass to be stable again."
Eventually, the star shrinks to about 40 solar masses, but even then
the celestial fireworks aren't over, said Woosley. It contracts to an
iron-rich core that collapses, ending with a searing gamma-ray burst
Stars that are between 90 and 30 times the mass of the Sun are rare
beasts, especially in our own galaxy, the Milky Way. But Woosley
believes they may have been more common in the infancy of the Universe.
A rival theory, meanwhile, is offered in Nature by Dutch astronomers
Simon Portegies Zwart and Edward van den Heuvel of the University of
They suggest that SN 2006ga could not have been created from a single
star, but from two very large stars that collided.
Their calculations are based on what happens in a young, dense cluster
of stars that are commonly seen at the centre of galaxies.