Scientists perplexed by unprecedented radio pulses coming from dormant star

‘We had never seen anything like this before,’ says researcher

Scientists have been left perplexed by unprecedented radio signals coming from a previously dormant star.

The star, known as XTE J1810-197, is a magnetar – a type of neutron star that are also the strongest magnets in the universe. It is the closest magnetar to Earth that we know of, at a relatively close 8,000 light years away.

Now scientists say that it appears to be sending out radio pulses that do not fit with expectations.

​”Unlike the radio signals we’ve seen from other magnetars, this one is emitting enormous amounts of rapidly changing circular polarisation. We had never seen anything like this before,” said Marcus Lower, a postdoctoral fellow at Australia’s national science agency, CSIRO, who led the work.

It is already surprising to detect radio signals from a magnetar at all, and XTE J1810-197 was already of interest as one of only a few to do so. But now scientists have found that those pulses are emitting a kind of spiralling light that was completely unexpected.

Light from magnetars is usually polarised. But the light from this magnetar is circularly polarised, meaning that it appears to form a spiral as it moves through space.

​XTE J1810-197 was the first known magnetar to send out radio signals, in 2003. But it then went silent for more than a decade – and now has woken back up.

The pulses suggest that there is more happening on the star than we had realised. It could change our understanding of intense magnetic fields and the environments around them, scientists said.

​”The signals emitted from this magnetar imply that interactions at the surface of the star are more complex than previous theoretical explanations,” said Manisha Caleb from the University of Sydney, a co-author on the study.

Scientists do not know why it is happening.

​“Our results suggest there is a superheated plasma above the magnetar’s magnetic pole, which is acting like a polarising filter,” Dr Lower said.

​“How exactly the plasma is doing this is still to be determined.”

A study describing the findings, ‘Linear to circular conversion in the polarized radio emission of a magnetar’, is published in Nature Astronomy.