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NASA Chandra X-ray Observatory Discovers Cosmic Fireball
11/28/2007
Press Release
Source:
Marshall Space
Flight Center
One of the fastest moving stars ever
seen has been discovered with NASA's Chandra X-ray Observatory. This
cosmic cannonball is challenging theories to explain its blistering
speed.
Astronomers used Chandra to observe a neutron star, known as RX
J0822-4300, over a period of about five years. During that span,
three Chandra observations clearly show the neutron star moving away
from the center of the Puppis A supernova remnant. This remnant is
the stellar debris field created during the same explosion in which
the neutron star was formed about 3700 years ago.
By combining how far it has moved across the sky with its distance
from Earth, astronomers determined the neutron star is moving at
over 3 million miles per hour. At this rate, RX J0822-4300 is
destined to escape from the Milky Way after millions of years, even
though it has only traveled about 20 light years so far.
"This star is moving at 3 million miles an hour, but it's so far
away that the apparent motion we see in five years is less than the
height of the numerals in the date on a penny, seen from the length
of a football field," said Frank Winkler of Middlebury College in
Vermont. "It's remarkable, and a real testament to the power of
Chandra, that such a tiny motion can be measured."
"Just after it was born, this neutron star got a one-way ticket out
of the Galaxy," said co-author Robert Petre of NASA's Goddard Space
Flight Center in Greenbelt, Md. "Astronomers have seen other stars
being flung out of the Milky Way, but few as fast as this."
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. The
hypervelocity stars are thought to have been ejected by interactions
with the supermassive black hole in the Galaxy's center.
This neutron star, by contrast, was flung into motion by the
supernova that created Puppis A. The data suggest the explosion was
lop-sided, kicking the neutron star in one direction and the debris
from the explosion in the other.
The supernova was precipitated when the core of a massive star
imploded to form a neutron star. Computer simulations show that the
infall of the outer layers of the star onto a neutron star releases
an enormous amount of energy. As this energy propagates outward, it
can reverse the infall and eject the outer layers of the star at
speeds of millions of miles per hour. Due to the complexity of the
flow, the ejection is not symmetric, leading to a rocket effect that
propels the neutron star in the opposite direction.
The breakneck speed of the Puppis A neutron star, plus an apparent
lack of pulsations from it, is not easily explained by even the most
sophisticated supernova explosion models.
"The puzzle about this cosmic cannonball is how nature can make such
a powerful cannon," said Winkler. "The high speed might be explained
by an unusually energetic explosion, but the models are complicated
and hard to apply to real explosions."
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.
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.
Additional information and images are available at:
http://chandra.harvard.edu
http://chandra.nasa.gov
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