Nov. 30, 2007 -- Astronomers have spotted and clocked a star ripping through the Milky Way at more than 3,000,000 miles per hour. That sort of excessive speed -- one of the fastest ever measured -- is certain to kick the star out of the Milky Way.
The star itself is a neutron star dubbed RX J0822-4300. It's the dead, very dense remnant of what was once a large star. It has been observed over the last five years by the Chandra X-ray Observatory as the star has shot away from the 3,700-year-old remnant of a supernova, or exploding star, known as Puppis A.
In fact, the supernova is precisely what sped up the neutron star.
The pair was once a set of companion stars, then one blew up, apparently in a very lopsided manner, and shot RX J0822-4300 out just like a cannonball out of a cannon.
"The analogy is not bad," said astronomer Frank Winkler of Middlebury College in Vermont. Winkler is the coauthor of a paper on the cannonball of a neutron star in the Nov. 20 issue of The Astrophysical Journal.
By putting together three Chandra observations over five years that show the changing position of the neutron star, along with measurements of the star's distance, it was a straightforward matter to calculate its speed.
Previous measurements in X-rays had hinted at a lopsided supernova explosion, Winkler told Discovery News. They had detected shards of the exploding star's core, which are still-intact lumps of pure oxygen created by nuclear fusion, shooting off in one direction in Puppis A. So it wasn't entirely surprising to find the neutron star being kicked.
It's the speed that is a surprise.
At three million miles per hour RX J0822-4300 has ample velocity to escape the Milky Way forever. However, even at such a great speed, it will take millions of years to travel all the way out of the galaxy.
"When you have an exceptional speed, it's bye-bye baby," said Winkler of RX J0822-4300's galactic escape velocity.
Ten other "hypervelocity" stars, as astronomers call them, have been observed, but they are associated with the supermassive black hole at the center of the galaxy, said stellar researcher Scott Kenyon of the Smithsonian Astrophysical Observatory.
The tremendous gravity of the black hole helps to speed up the stars and sling them away.
"This (neutron star) is a different phenomenon than what we call hypervelocity stars," said Kenyon.
Stars kicked by supernova are more often referred to as "run-away stars," he said. What's more, both kinds of fast-moving stars are probably not as rare as they appear. "For every one we see there are many we don't."
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