Unusual radio signal from a nearby star has scientists perplexed

An unusual radio signal, coming from the magnetar XTE J1810-197, the “magnetic star” closest to Earth, is causing scientists to discuss because the waves transmitted by this extreme celestial body are as “never seen before”. The first to be surprised were the researchers using the Murriyang, the 64-metre radio telescope at the Parkers Observatory in Australia, managed by the Commonwealth Scientific and Industrial Research Organization (CSIRO), who detected the radio emission, detailed in an article just published on Nature Astronomy.

What is the XTE J1810-197 magnetar and why its signal is different

XTE J1810-197, the scholars explain, is one magnetar (from the English terms magnettic And star, literally “magnetic star”), a type of neutron star that has an enormous magnetic field, billions of times greater than Earth’s. About 8,000 light years away from Earth, this magnetar it remained dormant for about 10 years, but recently it has returned to emitting radio pulses. However, compared to the signals of other magnetars, XTE J1810-197 emits completely unexpected bright radio pulses, because highly circularly polarizeda sort of spiral light that propagates in space.

To date, only six magnetars capable of emitting radio pulses are known, of which the majority emit polarized light. However, none of them, with the exception of XTE J1810-197, have ever been documented a circular polarizationsuggesting the possibility that “interactions on the surface of the star are more complex than previous theoretical explanations” says Dr Manisha Caleb of the University of Sydney and co-author of the study, which paves the way for insights into the physics of intense magnetic fields and the environments surrounding these extreme objects.

While it’s unclear why this magnetar behaves so differently, the team hypothesizes that above its magnetic pole “there is superheated plasmawhich acts as a polarizing filter – says Dr. Marcus Lower, a CSIRSO postdoctoral researcher who coordinated the analysis – . However, the exact way the plasma can exert this action has yet to be determined”.

XTE J1810-197 was first observed emitting radio signals in 2003 but mysteriously stopped doing so in 2008, remaining for ten years in silence. As of December 2018, its signals were again detected by the University of Manchester’s 76-metre Lovell telescope, at the Jodrell BankPoi Observatory, and then tracked by the Murriyang, which has since been instrumental in observing radio emissions of the magnetar. Designed by CSIRO engineers, the Murriyang has in fact allowed more precise measurements, because it is highly sensitive to changes in brightness and polarization over a wide range of radio frequencies.

The unusual behavior of XTE J1810-197 could change our understanding of magnetars, providing insights “on a series of extreme phenomenasuch as plasma dynamics, X-ray and gamma-ray bursts, and fast radio bursts” the scientists concluded.