| 
Artist's illustration of supernova SN 2006gy
Credit: Illustration: NASA/CXC/M.Weiss; X-ray: NASA/CXC/UC Berkeley/N.Smith et al.; IR: Lick/UC Berkeley/J.Bloom & C.Hansen
|
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."
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."
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
US $164.99
