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Astronomers estimate the newly discovered pulsar has streaked across about a third of the night sky since it was created in a supernova 2.5 million years ago (Image: Bill Saxton/NRAO/AUI/NSF)

Astronomers have spotted the fastest moving stellar corpse to date – and it appears to be headed straight out of our galaxy.

A team from the US National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico, and the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, US, clocked the dead star at 1100 kilometres per second.

The object, called B1508+55, is a rotating neutron star, or pulsar. It is the superdense core of a massive star that exploded as a supernova about 2.5 million years ago. The explosion seems to have ejected the pulsar with such force that it will eventually escape the Milky Way entirely, says team member Shami Chatterjee, an astronomer with NRAO and CfA.

However, current simulations of supernovae have never produced such breakneck speeds. In the models, the newly formed neutron star starts out fast but soon slows down when material from the outer layers of the exploded star crashes back onto it. In 2004, the first 3D model of a supernova found that the blast could send a neutron star flying at about 200 kilometres per second - nearly six times slower than the new record holder.

Kick velocities

"I think everyone believes that supernova explosions do in nature provide these [higher] kick velocities," Chatterjee told New Scientist. "It's just that our simulations are not quite there yet."

The researchers watched this pulsar for two years with the Very Long Baseline Array – a collection of 10 radio-telescopes scattered from Hawaii to the US Virgin Islands. They determined the pulsar lies 7700 light years away and gauged its speed by observing how its position on the sky changed in that time.

From this, they traced its route backwards to its likely birthplace 2.5 million years ago in a region full of huge stars in the constellation Cygnus. The stars are so massive that they will eventually blow up as supernovae, potentially spawning other speedy stellar corpses.

Journal reference: Astrophysical Journal Letters (vol 630, p L61)

# posted by dark master : 9/06/2005 09:22:00 AM