"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.

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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Chandra X-ray Observatory
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