Strange, Super-Sized Pulsar Stumps Scientists

by Nancy Atkinson on May 16, 2008


Astronomers have discovered a fast-spinning, super-sized pulsar in a stretched-out orbit around an apparent Sun-like star. This combination (as well as that many hyphenated words in one sentence) has never seen before, and astronomers are puzzled about how this bizarre system developed. “Our ideas about how the fastest-spinning pulsars are produced do not predict either the kind of orbit or the type of companion star this one has,” said David Champion of the Australia Telescope National Facility. “We have to come up with some new scenarios to explain this weird pair.”

Pulsar J1903+0327, a rotating neutron star, is unusually massive for its type. It spins on its axis 465 times every second, while typical pulsars spin a few times a second. Located nearly 21,000 light-years from Earth, its elongated orbit takes it around its companion star once every 95 days. And the companion star is quite unusual as well: many pulsars pair up with a white dwarf star or another neutron star, but infrared images of the system show a Sun-like star along with the pulsar.

“This combination of properties is unprecedented. Not only does it require us to figure out how this system was produced, but the large mass may help us understand how matter behaves at extremely high densities,” said Scott Ransom of the National Radio Astronomy Observatory.

The image above shows the size and shape of Earth’s orbit around the sun compared to the orbits of Pulsar J1903+0327 and its possible Sun-like companion star. 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 1000. The pulsar, with its magnetic field and beams of radiation, is too large by a factor of about 100,000.

This pulsar was first detected in 2006 with the Arecibo radio telescope in Puerto Rico, with subsequent observations by the Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, the Westerbork radio telescope in the Netherlands, and the Gemini North optical telescope in Hawaii.

It’s possible that the pulsar may be part of a triple, not a double, star system. In this case, the pulsar’s 95-day orbit is around a neutron star or white dwarf that’s not been detected yet, not the Sun-like star seen in the infrared image. The Sun-like star would then be in a more-distant orbit around the pulsar and its close companion. But this, too would be highly unusual.

“We’ve found about 50 pulsars in binary systems. We may now have found our first pulsar in a stellar triple system,” Ransom said.

Further studies are underway to get a better understanding of what seems to be a highly unusual system.

“This is a fascinating object that has a lot to teach us about physics. It’s going to be exciting to peel away the mystery of how this thing came to be,” Champion said.

Original News Source: National Radio Astronomy Observatory

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Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

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