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November
28, 2007: Astronomers using NASA's Chandra X-ray
Observatory have discovered one of the fastest stars ever
seen. It's a "cosmic cannonball" that is challenging
theories to explain its blistering speed.
 The
name of the star is RX J0822-4300. It's a neutron star created
by the Puppis A supernova explosion about 3700 years ago.
Three Chandra observations clearly show the neutron star moving
away from the center of the blast. Speed: 3 million mph! At
this rate, RX J0822-4300 is destined to escape the Milky Way
just millions of years from now.
Right:
Chandra X-ray Observatory images of "cannonball star"
RX J0822-4300. [More]
"This
neutron star has got a one-way ticket out of the Galaxy,"
says Robert Petre of NASA's Goddard Space Flight Center in
Greenbelt, Md, one of the study's co-authors. "Astronomers
have seen other stars being flung out of the Milky Way, but
few as fast as this."
Although
the star is moving extremely rapidly, its motion is not easy
to see, notes lead author Frank Winkler of Middlebury College
in Vermont. "The star is so far away that the motion
we see in five years is less than the height of the numerals
in the date on a penny held 100 yards away. It's remarkable,
and a real testament to the power of Chandra, that such a
tiny angle can be measured."
This
isn't the first time astronomers have found million-mph stars.
So-called "hypervelocity stars" have been previously
discovered shooting out of the Milky Way with speeds around
one million miles per hour. One key difference between RX
J0822-4300 and these other reported galactic escapees is the
source of their speed. Hypervelocity stars are thought to
have been ejected by interactions with a supermassive black
hole in the Galaxy's center, which can act as a sort of "gravitational
slingshot." This
neutron star, by contrast, was flung into motion by a supernova.
Data suggest the explosion was lop-sided, kicking the neutron
star in one direction and the debris from the explosion in
the other.
Above:
A composite image showing the off-center location of RX J0822-4300
in the Puppis A supernova remnant. [More]
The
breakneck speed of the Puppis A neutron star is not easily
explained, however, by even the most sophisticated supernova
explosion models. "The puzzle about this cosmic cannonball
is how nature can make such a powerful cannon," says
Winkler. "The velocity might be explained by an unusually
energetic explosion," but researchers remain unsure.
It's
a high-speed mystery—courtesy of Chandra.
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The research by Winkler and Petre
was published in the November 20 issue of 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.
Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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Other
recent work on RX J0822-4300 was published by C.Y. Hui
and Wolfgang Becker, both from the Max Planck Institute
for Extraterrestrial Physics in Munich, in the journal
Astronomy and Astrophysics in late 2006. Using two of
the three Chandra observations reported in the Winkler
paper and a different analysis technique, the Hui group
found a speed for RX J0822-4300 that is about two-thirds
as fast, but with larger reported margins of error.
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