January 07, 1993

Article at Reuters

Astronomers find closest pulsar to Earth

The pulsar PSR J0437-4715, a spinning husk of the collapsed star

By Wilson da Silva

SYDNEY – Astronomers in Australia have discovered a pulsar about 25 times closer to Earth than any other star of its kind and possibly visible from the ground with telescopes, they said on Thursday. 

The pulsar, a spinning husk of the collapsed star PSR J0437-4715, was found in July by a group of Australian, British, American and Italian astronomers using the Parkes radio telescope in outback New South Wales. 

The pulsar is the spinning core of an exploded sun, British astronomer and team leader Simon Johnston told Reuters. It emits a narrow radio beam which, because of the rotation, sweeps across Earth’s line of sight causing the observed pulses. 

Light from the newly-discovered pulsar takes about 400 years to reach Earth, he added. Light from the sun takes about eight minutes to reach Earth. 

The pulsar spins 175 times a second and is about 10 km (16 miles) wide but weighs 1.5 times as much as our sun, he said. 

“A teaspoon of the millisecond pulsar would weigh 100,000 tonnes,” Johnston said. “We’re hoping to see it optically but it’s a very hard to do.” 

The pulsar has a companion sun, a collapsed white dwarf star, which is bright and spins around it every six days. 

The group found the dwarf companion star on old photographic plates of the night sky but say capturing the elusive and faint pulsar will be difficult. 

The astronomers submitted a paper to the British scientific journal Nature and will now try to photograph the pulsar. 

Fast-spinning pulsars are on average found by radio telescopes about 10,000 light years away, too far and too dim for optical telescopes. 

The only other close pulsar is an old star which spins once a second and has no companion star. 

Johnston said the find conforms to theories that millisecond pulsars are old dying neutron stars which are recycled back to life when matter ejected by its companion sun is dumped on its core, rekindling its ancient heart. 

A pulsar is an ageing sun that runs so low on stellar fuel it collapses into itself, eventually triggering a cataclysmic explosion that blows most of its mass away. 

The neutron core left behind continues to compress itself until it is so heavy that a coffee cup if brought to Earth would weigh millions of tonnes. 

Johnston’s group has found 50 new pulsars in the last year, adding to the 600 already identified in our Milky Way galaxy, a group of about 100 billion stars that makes up our stellar backyard. There are only 20 known millisecond pulsars.