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Some pulsars lose their steady beat

New discoveries hint at hidden population of neutron stars

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9:00am, January 6, 2017
Arecibo Observatory

IRREGULAR PULSARS  Two pulsars discovered by the Arecibo Observatory (shown) spend most of their time not pulsing, suggesting a large population of undiscovered pulsars in the Milky Way.

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GRAPEVINE, TEXAS — A pair of cosmic radio beacons known as pulsars keep switching off and on, suggesting that there might be vast numbers of undiscovered pulsars hiding in our galaxy.

Pulsars are rapidly spinning neutron stars, the ultradense cores left behind after massive stars explode. Neutron stars are like lighthouses, sweeping a beam of radio waves around the sky. Astronomers see them as steady pulses of radio energy.

But at least two in the Milky Way seem to spend most of their time turned off, Victoria Kaspi, an astrophysicist at McGill University in Montreal, reported January 4 at a meeting of the American Astronomical Society. One, first detected at Arecibo Observatory in Puerto Rico in November 2011, only pulses about 30 percent of the time. Another, also discovered at Arecibo, laid down a steady beat just 0.8 percent of the time when observed in 2013 and 2015. Then starting in August 2015, it abruptly jumped to being on 16 percent of the time for several months.

When sending out pulses, the pulsars seem to behave like any other pulsar, Kaspi said. “You wouldn’t know that they have this dual personality.” Researchers don’t yet know why some pulsars behave this way. But Kaspi said that it’s probably tied to changes in their magnetic fields, which astronomers think help control the radio beacons.

These two intermittent pulsars join three others that had been previously observed. Given that most spend much of their time off, Kaspi said, astronomers might be missing a large population of pulsars in the Milky Way.

Citations

V.M. Kaspi. Part-time pulsars. 229th meeting of the American Astronomical Society, January 4, 2017, Grapevine, Texas.

Further Reading

A. Grant. Pulsar pair ripples spacetime. Science News. Vol. 189, January 23, 2016, p. 16.

C. Crockett. Pulsar pulverizes an asteroid. Science News Online, February 24, 2014.

N. Drake. Weird pulsars debut at Beijing astronomy meeting. Science News Online, August 21, 2012.

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