Pulsar shows puzzling behavior

Posted by Emma Woollacott

Astronomers are baffled by the discovery of a pulsar - a tiny spinning stars, heavier than the sun and smaller than a city - that emits different types of radiation at different times.

In just a few seconds, PSR B0943+10 can damp down its radio waves, while at the same time making its X-ray emissions much brighter - something that 'challenges all proposed pulsar emission theories', says the team.

Rather like lighthouses, pulsars shine paired beams of radio waves and other radiation for trillions of miles, showing up as flashes or pulses in telescopes on Earth. This one was already known to flip on and off every few hours between strong and weak radio emissions.

But by monitoring it simultaneously in X-rays and radio waves, the team has found that this pulsar shows the same behaviour, only in reverse, when observed at X-ray wavelengths.

"As well as brightening in the X-rays we discovered that the X-ray emission also shows pulses, something not seen when the radio emission is bright," says University of Vermont astrophysicist Joanna Rankin. "This was completely unexpected.”

No current model of pulsars can explain this behavior, with all theories to date suggesting that X-ray emissions would follow radio emissions.

By studying the emission from the pulsar at different wavelengths, the team had hoped to discover which of various possible physical processes take place in the vicinity of the magnetic poles of pulsars. Instead, however, their observations challenge all existing models for pulsar emission.

Recent studies indicate that the switch between 'radio-bright' and 'radio-quiet' states is linked to the pulsar's dynamics. As pulsars rotate, their spinning period slows down gradually, and in some cases this seems to happen in conjunction with the pulsar switching between bright and quiet states.

This correlation has led astronomers to suggest a connection between the star’s surface and the much-larger surrounding magnetosphere, which may extend up for 30,000 miles. The new observations suggest that a temporary ‘hotspot’ may be appearing close to the pulsar’s magnetic pole and switching on and off with the change of state.

In order for the radio emission to vary so radically in  such short timescales, the pulsar's global environment must undergo a very rapid – and reversible – transformation.

"If that is true, it means the entire magnetosphere is alive and connected in very important ways," says Rankin.