One of the strangest stars in the Milky Way just got even stranger. It is a magnetar called XTE J1810-197 and was discovered in 2003 emitting only radio waves. In 2008… it stopped and almost disappeared from our sight. It then flared up again in 2018. However, this time there was something strange about the radiation it emitted.

Now scientists have analyzed these radio waves in two separate papers, and the results are surprising. These low-frequency electromagnetic emissions are distorted in a way we haven’t seen before, and the star appears to oscillate.

“Unlike the radio signals we see from other magnetars, this magnetar emits a large amount of rapidly changing circular polarization,” says Marcus Lower, an astrophysicist at CSIRO in Australia who led the first paper. “We’ve never seen anything like this before.”

“We expected to see some changes in the polarization of the radiation from this magnetar, as we know from other magnetars,” explains Gregory Desvignier of the Max Planck Institute for Radio Astronomy (MPIfR) in Germany, who conducted the second study. “But we did not expect these changes to be systematic enough to exactly match the behavior that would be caused by the star’s oscillations.”

All stars are special in their own way, but magnetars are perhaps the strangest of the strange. These are very young neutron stars, the collapsed cores of dead massive stars that themselves went supernova and expelled most of their material in a massive explosion. The remaining core collapses under the influence of gravity and tight – About 2.3 times the mass of the Sun, compressed into a sphere just 20 kilometers (12 miles) in diameter.

After this collapse process, neutron stars have an incredibly strong magnetic field for a short time. These are actually the most magnetic things in the universe; Their magnetic fields are 1000 times stronger than a normal neutron star and quadrillion times stronger than Earth.

This causes them to act a little strange. For example, scientists believe that the constant tug of war between the magnetar’s magnetic field and gravity causes it to sometimes explode in giant earthquakes and send out bursts of radio waves that we call fast radio bursts. Thus, XTE J1810-197 ceases to be a magnetar and turns into a freak even without on-off. But recent activity is unprecedented and could provide new insights into these mysterious stars.

Lower, Desvin and their colleagues measured a property of the light emitted by the star, known as polarization. That’s when the oscillation of the light reaching us is directed in the desired direction. It is normal for magnetic light to be polarized, rotated by the strong magnetic field it must pass through to reach us.

Typically magnetars emit mostly linearly polarized light and a small amount of spirally polarized light. Lauer and his team found that XTE J1810-197 emits a tremendous amount of circularly polarized light.

Theory suggests this might happen when light has to pass through the thick, superheated “soup” of particles found in a neutron star’s magnetic field. The behavior of XTE J1810-197 doesn’t exactly match this prediction, but the researchers have some ideas.

“Our results show that a superheated plasma exists above the magnetic pole of the magnetar, which acts as a polarization filter,” says Lower. “Exactly how plasma does this has not yet been determined.”