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May
7, 2007: The brightest stellar explosion ever recorded
may be a long-sought new type of supernova, according to observations
by NASA's Chandra X-ray Observatory and ground-based optical
telescopes. This 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
of California at Berkeley, who led a team of astronomers from
California 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."
Above:
An artist's illustration of supernova SN 2006gy. [More]
Astronomers
think many of the first stars in the Universe were this massive,
and this new supernova may thus provide a rare glimpse of
how those first generation 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.
Above:
Optical (left) and X-ray (right) images of SN 2006gy. The
dimmer source at lower-left is the nucleus of the host galaxy.
The brighter source at upper-right is the stellar explosion.
The supernova was as bright as the entire core of a galaxy!
[More]
"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."
 Right:
eta Carinae--a supernova waiting to happen in our own galaxy?
The giant star is highlighted by diffraction spikes in this
astrophoto taken by Brad Moore. [More]
Supernovas
usually occur when massive stars exhaust their fuel and collapse
under their own gravity. In the case of SN 2006gy, however,
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 that spew their remains - 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 [sprinkles] the galaxy with large quantities of
newly made elements and the other locks them up forever in
a black hole."
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The
results from Smith and his colleagues will appear in The Astrophysical
Journal. NASA's Marshall Space Flight Center, Huntsville,
Ala., manages the Chandra program for the agency's Science
Mission Directorate. The Smithsonian Astrophysical Observatory
controls science and flight operations from the Chandra X-ray
Center in Cambridge, Mass. Additional information and images
are available at http://chandra.nasa.gov .
Source: NASA Press Release | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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