http://science.nasa.gov/headlines/y2007/28nov_cosmiccannonball.htm?list924016

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.