Faster Than a Speeding Bullet

UNLIKE THE WANDERING PLANETS, the stars appear to be fixed in the sky. Astronomers know, though, that this is only an illusion. The stars are moving too, floating lazily through space. At least, most of them are floating: careful observations from a land-based telescope of a star known as PSR 2224+65, in the constellation Cepheus, have revealed that this particular object is virtually shooting through the galaxy. Now 6,000 light-years from Earth and zipping along at more than 2 million m.p.h., it is going 10 times as fast as the speediest star ever seen, and 100 times as fast as most stars. At this rate, it will almost certainly escape the Milky Way altogether.

Not that PSR 2224+65 is in any sense an ordinary star. It is a pulsar, the superdense ash left behind when a star exploded -- about a million years ago -- in the phenomenon known as a supernova. The blast blew off the star's outer layers and flung the 3,000 trillion trillion ton, Manhattan-size pulsar through space. The dead star generates an enormous magnetic field, which in turn sends out powerful radio pulses (hence the name pulsar).

It also emits radiation that plows through the sparse gases of interstellar space. The radiation, says Cornell astronomer James Cordes, who co-authored a report on the pulsar in this week's Nature, "creates a wake, like a boat going across a choppy lake." Seeing how the wake, which appears to be shaped roughly like a guitar, interacts with other matter will help scientists understand what lies in the spaces between the stars. The very existence of one high-velocity pulsar implies that there must be others, some of which have undoubtedly escaped into deep space. Scientists hope to use the Hubble telescope to spot and study more superfast pulsars -- if NASA's mission to fix the hobbled instrument succeeds.