One of the fastest moving stars ever seen is challenging theories to explain its blistering speed.

The cosmic cannonball, a neutron star known as RX J0822-4300, was discovered with NASA's Chandra X-ray Observatory.

Astronomers used five years of Chandra observations to show that the rogue star is careening away from the Puppis A supernova remnant, leftovers of a star that exploded about 3,700 years ago. The neutron star is racing out of our Milky Way Galaxy at about 3 million mph (4.8 million kph).

"Just after it was born, this neutron star got a one-way ticket out of the galaxy," said co-author Robert Petre, an astronomer at 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."

Other hypervelocity stars known to be exiting the Milky Way move at speeds about one-third as great—likely shot toward interstellar space by an aggressive, supermassive black hole at our galaxy's center.

In the case of RX J0822-4300, however, a tremendous lopsided supernova explosion rocketed the neutron star to its blinding speed. It has traveled 20 light-years thus far, and will take millions of years to escape the clutches of the Milky Way.

Despite using advanced computer models to simulate how such a stellar rocket could form, astronomers are at a loss of words.

"The problem with discovering this cosmic cannonball is we aren't sure how to make the cannon powerful enough." said Frank Winkler, an astronomer at Middlebury College in Vermont. "The high speed might be explained by an unusually energetic explosion, but the models are complicated and hard to apply to real explosions."

Winkler and Petre's research is detailed in a recent issue of the Astrophysical Journal.