Pulsars are fast-spinning stars that emit regular beams of light known for their clocklike regularity. So, when one strangely turned off for a year and a half, astronomers were surprised to find that this abnormality could help them solve the longstanding mystery of what makes these flashing stars tick.
Despite more than forty years of study, astronomers still can't nail down what causes these rapidly rotating stars to pulse. But when one, called PSR J1841, turned off for 580 days, it gave astronomers a glimpse of how pulsars behave when they can't be seen.
In December 2008, Fernando Camilo, of Columbia University in New York, was using the Parkes telescope in Australia to search for a known object when he found a steadily flashing star in his field of view. He quickly identified it as a pulsar that was spinning once every 0.9 seconds — a fairly standard rotation.
"I wasn't too excited," Camilo admitted to SPACE.com.
"At first, I thought there was something wrong with my equipment," Camilo said.
"I realized, it's really off now."
"Pulsars generally are steady emitters of radio pulses," Camilo said.
But "for a few rotations, some turn off."
Only one other pulsar has been found to vanish for more than a few minutes at a time — PSR B1931+24 turns on for a week at a time and then shuts off for a month.
The stars' spin causes their light to appear to pulse. Over their 30-million-year life spans, the pulsation slows gradually, until they finally burn out. [Supernova Photos: Great Images of Star Explosions]
"When it's off, we literally don't see anything," Camilo said.
Instruments can't capture that information with precision for pulsars that turn off for only a few minutes.
Massive currents in the magnetospheres of the neutron stars provide some of the torque that slows their spin. When the currents stop flowing, the pulsing gradually slows down. But astronomers still don't know what is stopping the currents from flowing.
"These are extremely massive stars — the mass of the sun, jam-packed into the size of a city," Camilo said. "They need a lot of energy to change their rotation. It's something energetic happening near the surface of the pulsar and its magnetosphere."
Furthermore, the discovery hints at the possibility that other known pulsars could be in the midst of their own long "on" period.
Camilo notes, however, that pulsars live for 30 million years, while they've only been studied since the 1970s.
"We are just sampling a short portion of [a pulsar's] life," he said.
A pulsar could have an "on" period of a hundred years.
"Some of the pulsars we know and love, and have been studying for 40-odd years, and consider to be reliable standards, maybe one of these years or decades one of them will just turn off."
