Star Dies in Monstrous Explosion
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A star about 150 times more massive than our sun has exploded in a nearby
galaxy in what could be a long-sought new type of supernova, according
to NASA scientists.
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The discovery indicates that
violent explosions of extremely
massive stars were relatively
common in the early universe,
and that a similar explosion
may be ready to go off in our
own galaxy.
"This was a truly monstrous
explosion, a hundred times more
energetic than a typical supernova,"
said Nathan Smith of the University
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of California at Berkeley, who led a
team of astronomers from California
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Artist's illustration of supernova SN 2006gy
(courtesy of NASA/CXC/M.Weiss).
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and the University of Texas in Austin.
"That means the star that exploded might have been as massive as a star can
get, about 150 times that of our sun. We've never seen that before," Smith said.
Astronomers think many of the first generation of stars were this massive, and
this new supernova may thus provide a rare glimpse of how the first stars died.
It is unprecedented, however, to find such a massive star and witness its
death. The discovery of the supernova, known as SN 2006gy, provides
evidence that the death of such massive stars is fundamentally different from
theoretical predictions.
"Of all exploding stars ever observed, this was the king," said Alex Filippenko,
leader of the ground-based observations at the Lick Observatory at Mt.
Hamilton, Calif., and the Keck Observatory in Mauna Kea, Hawaii. "We were
astonished to see how bright it got, and how long it lasted."
The Chandra observation allowed the team to rule out the most likely
alternative explanation for the supernova: that a white dwarf star with a mass
only slightly higher than the sun exploded into a dense, hydrogen-rich
environment. In that event, SN 2006gy should have been 1,000 times brighter
in X-rays than what Chandra detected.
"This provides strong evidence that SN 2006gy was, in fact, the death of an
extremely massive star," said Dave Pooley of the University of California at
Berkeley, who led the Chandra observations.
The star that produced SN 2006gy apparently expelled a large amount of mass
prior to exploding. This large mass loss is similar to that seen from Eta
Carinae, a massive star in our galaxy, raising suspicion that Eta Carinae may
be poised to explode as a supernova.
Although SN 2006gy is intrinsically the brightest supernova ever, it is in the
galaxy NGC 1260, some 240 million light years away. However, Eta Carinae is
only about 7,500 light years away in our own Milky Way galaxy.
"We don't know for sure if Eta Carinae will explode soon, but we had better
keep a close eye on it just in case," said Mario Livio of the Space Telescope
Science Institute in Baltimore, who was not involved in the research. "Eta
Carinae's explosion could be the best star-show in the history of modern
civilization."
Supernovas usually occur when massive stars exhaust their fuel and collapse
under their own gravity. In the case of SN 2006gy, astronomers think that a very
different effect may have triggered the explosion. Under some conditions, the
core of a massive star produces so much gamma ray radiation that some of
the energy from the radiation converts into particle and anti-particle pairs. The
resulting drop in energy causes the star to collapse under its own huge gravity.
After this violent collapse, runaway thermonuclear reactions ensue and the star
explodes, spewing the remains into space. The SN 2006gy data suggest that
spectacular supernovas from the first stars - rather than completely collapsing
to a black hole as theorized - may be more common than previously believed.
"In terms of the effect on the early universe, there's a huge difference between
these two possibilities," said Smith. "One pollutes the galaxy with large
quantities of newly made elements and the other locks them up forever in a
black hole.
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