The Mystery of the Vanishing Pulsar 23,000 Light Years Distant

                 Vanishing-pulsars-PSR-J1841-0500 (1)

While studying the globelike supernova remnant, astronomers discovered a new pulsar spinning once every 0.9 seconds, orbiting 22.8 light-years from the sun in the Scutum-Centaurus spiral arm of our Milky Way galaxy. After shining for at least a year, the pulsar, located inside the white circle in the image above, suddenly vanished. 


In 1967, regular pulses of radiation were detected coming from space – so regular that their discoverers thought they could be signals from an extraterrestrial civilization. That hypothesis was soon abandoned and the source was named a pulsar, or pulsing, fast-spinning stars that emits regular beams of light known for its clocklike regularity. Since then, the metronomic emissions of gamma rays, X-rays or radio waves from pulsars has made them cosmic lighthouses.

Yet, despite more than forty years of study, astronomers still can't determine what causes these stars to pulse. Of the 2,000 known pulsars, less than 100 have been known to stop pulsing completely. For most, the cessation is on the order of only a few minutes. But when one, called PSR J1841, turned off for 580 days, it gave astronomers a glimpse of how pulsars behave when the go into a fade phase.

Enter Fernando Camilo, an astronomer at Columbia University in New York, was astounded when the radio pulsar he had discovered and had been observing for a year – PSR J1841-0500 – suddenly stopped beaming its regular bursts. 

"At first I had a hard time believing what I was seeing," he told New Scientist. "For the past year, the pulsar had been so reliable, pulsing brightly once every 0.9 seconds. I thought there must be an error with the equipment."

Camilo continued observing the star at 5-minute intervals once a month either at the CSIRO Parkes Observatory in New South Wales, Australia, where it had been discovered, or at the National Radio Astronomy Observatory in Green Bank, West Virginia. A year and a half later, his hard work paid off when the star came back to life, pulsing brightly as well as adding to the mystery of what makes pulsars "tick."

The rotating magnetic field accelerates charged particles on the netron star's surface, somehow producing a beam of radiation along the magnetic field axis, which is at an angle to the pulsar's rotational axis, so it sweeps through space with a regularity similar to the light in a lighthouse. 
The beam of some X-ray-emitting pulsars is so regular that they rival atomic clocks for precision. This property is useful when searching for the effects of gravitational waves and in satellite navigation.

In the 1970s, some regular pulsars were spotted switching off for a few seconds to a few minutes, a phenomenon known as "nulling". In the past decade, a new class of pulsars –rotating radio transients, or RRATs. –has been found , in which the silences can range from minutes to a few hours. Around the same time, a pulsar was found that pulsed for about a week and then switched off for about a month before repeating the cycle.

Jodrell Bank Observatory in England continually catalogs known pulsars in the northern hemisphere, and astronomers there have not observed other pulsars vanish after a week or a year, implying that such disappearances are rare.

"Is it possible that some pulsars can turn off for decades or centuries at a time? Is it possible that pulsars that we know and love, those that we have known since 1967 and those that are important for the study of all sorts of phenomena, will turn off at some point? A pulsar like this one makes you wonder," Camilo said.

The unpredictability of pulsars may be due to old age, Camillo says. As they get older, the rate at which they rotate gradually slows down as their energy vanishes into space. This makes it harder for the charged particles to be accelerated to the high speeds needed to maintain the light beam.

The Daily Galaxy via New Scientist, space.com and arxiv.org/abs/1111.5870

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