Astronomers baffled by weird, fast-spinning pulsar

WASHINGTON Thu May 15, 2008 10:18pm BST

A diagram shows a comparison of the sizes and strangely elliptical shapes of the orbits of the pulsar J1903+0327 and its apparently Sun-like companion star with the orbit of the Earth around the Sun. The sizes of the Sun and the possible companion star have been exaggerated by a factor of about 10, while that of the Earth has been exaggerated by a factor of about 1,000. The pulsar, with its magnetic field and beams of radiation, is too large by a factor of about 100,000. REUTERS/Bill Saxton, NRAO/AUI/NSF/Handout

A diagram shows a comparison of the sizes and strangely elliptical shapes of the orbits of the pulsar J1903+0327 and its apparently Sun-like companion star with the orbit of the Earth around the Sun. The sizes of the Sun and the possible companion star have been exaggerated by a factor of about 10, while that of the Earth has been exaggerated by a factor of about 1,000. The pulsar, with its magnetic field and beams of radiation, is too large by a factor of about 100,000.

Credit: Reuters/Bill Saxton, NRAO/AUI/NSF/Handout

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WASHINGTON (Reuters) - Astronomers are baffled after finding an exotic type of star called a pulsar apparently locked in an elongated orbit around a star much like the sun -- an arrangement defying what had been known about such objects.

The rapidly spinning pulsar -- an extraordinarily dense object created when a massive star exploded as a supernova -- is called J1903+0327 and is located about 21,000 light years from Earth, the astronomers said.

A light year is about 6 trillion miles, the distance light travels in a year.

"The big question is -- how in the heck did this thing form, because it doesn't follow our standard models of how these things form," astronomer Scott Ransom of the National Radio Astronomy Observatory in Charlottesville, Virginia, said in a telephone interview on Thursday.

This object is known as a millisecond pulsar because of its speedy whirl -- it spins on its axis 465 times per second.

Until now, all of the ones found orbiting with another star have been doing so with a white dwarf, another type of dying star. In each case, they shared a perfectly circular orbit. But this one has a very elongated orbit around a star similar in size and composition to our sun.

"What we have found is a millisecond pulsar that is in the wrong kind of orbit around what appears to be the wrong kind of star," astronomer David Champion of the Australia Telescope National Facility said in a statement. "Now we have to figure out how this strange system was produced."

It was detected using a radio telescope in Puerto Rico.

Pulsars are a rare type of neutron star whose strong magnetic fields channel lighthouse-like beams of light and radio waves that whirl around as the star spins.

Typical pulsars spin once a second to about 10 or 20 times a second. But millisecond pulsars spin far more rapidly.

The understanding had been that these started out as typical, slower-spinning pulsars, then built up speed after material expelled from another star reached the pulsar's surface, giving it momentum.

"If you were to ask any astronomer if we would have found a system like this, they would have said no. So this is a very big surprise," Ransom said.

The scientists, writing in the journal Science, speculate a third star -- perhaps a neutron star or white dwarf -- might be orbiting with the other two. Scientists know of about 100 pulsars in two-star, or binary, systems, and this might be the first in a triple-star system, Ransom said.

(Editing by Vicki Allen)

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