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"Undead" Star Torpedoes Current Theories

August 26, 1999
CSIRO Australia
Using CSIRO data a West Australian PhD student has found a star that is not supposed to exist.

Using CSIRO data a West Australian PhD student has found a star that is not supposed to exist. His discovery is published in today's issue of the journal Nature.

Matthew Young of the University of Western Australia studies pulsars - small spinning stars which send out beams of radio waves. As a pulsar spins its beam sweeps over the Earth and we see a radio 'blip'. By taking the pulsar's pulse astronomers measure how fast the star is spinning.

The new pulsar, called PSR J2144-3933, spins only once every eight seconds. "This is supposed to be way too slow," explains Mr Young.

"The theory says pulsars that spin slower than once every few seconds don't have the energy to put out pulses - their heartbeat stops and they die. This pulsar is on the slab, so to speak, but its heart is still beating. By rights it should be a corpse."

As a pulsar gets older its spinning slows down. So the new pulsar is quite aged, about 280 million years old.

The new pulsar's data was recorded in a large hunt for pulsars made with CSIRO's Parkes radio telescope, which has found well over half of all known pulsars.

Mr Young discovered the pulsar's long pulse period while looking for something else.

"I was looking for missing pulses, points at which the pulsar skips a beat. At first glance it seemed that this pulsar was missing two beats out of three. Then it became clear that it was really only beating a third as fast as we'd thought."

"This is a bit of a problem for the theories," says CSIRO's Dr Dick Manchester, co-leader of many pulsar searches with the Parkes telescope.

"For almost thirty years we've thought that pulsar beams are powered by an exotic process that makes matter and anti-matter. The theory also says that this pulsar spins too slowly for that process to occur - that it shouldn't be putting out radio waves. But it is."

There are a few things that could be wrong, he says.

"Perhaps the matter and anti-matter process is going on, but it can happen at lower spin rates than we thought. Or perhaps the pulses are powered by something else. Whatever the case, the theory needs a rethink."

Finding this pulsar implies that the pulsar population is a lot 'greyer' than was thought.

"We found this pulsar only because it's relatively nearby - about 600 light-years away," says Mr Young. "It has a small beam and a fairly weak signal. This means there could be a lot more slow, old pulsars lurking out there undetected. Our best guess is about 100 000 in the Galaxy - as many as all the other pulsars put together."

Astronomers are interested in pulsars for a number of reasons. "The matter that makes up pulsars is in the most condensed state it can be without turning into a black hole," Dr Manchester explains. "It's an extreme state and we don't fully understand it."

"As well, astronomers just love having these super-accurate clocks flying around in space, because they can be used to work out all sorts of things about the stars they orbit and even the space between the stars. One pulsar has been used to show that gravity waves are real."

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