Neutron stars are what's left over when a star goes nova. About the size of a good-sized city (20 miles in diameter or so), but containing all the mass of a normal-sized star, they are incredibly dense. A teaspoon of neutron star matter would weigh as much as several World War II-era battleships.

Frank Winkler of Middlebury College in Vermont and Robert Petre of NASA's Goddard Space Flight Centre used NASA's orbiting Chandra X-ray Observatory, taking pictures of the neutron star labeled RX J0822-4300 five years apart. Based on the estimated distance of 6500 light years, they calculated that the object was traveling at an astonishing 932 miles per second - faster than any such object yet seen.

"It’s a great measurement," says Shami Chatterjee of Cornell University, who has led similar studies in the past. "It shows that high velocity neutron stars may be even more common than we think." He adds that uncertainty about the distance to the neutron star's velocity means that the measurement could be flawed.