A powerful magnetic neutron star, or magnetar, “failed” when it destroyed an asteroid, causing it to emit a rapid radio burst and change its rotation rate.
For years, astronomers have been puzzled by an extremely powerful type of explosion known as a fast radio burst (FRB). These bursts occur randomly across the sky, last only a few milliseconds, and represent some of the most powerful explosions in the universe. But in 2020, astronomers hit a lucky break when they discovered an FRB in our own galaxy. Follow-up observations located the source of the FRB: a magnetar. Magnetars are a special type of neutron star (an ultradense remnant of a gigantic star that exploded), and they have the strongest magnetic fields in the universe. The strongest magnetars have magnetic fields quadrillion times stronger than Earth’s.
Shortly before the FRB appeared, astronomers saw something strange happen to the magnetar: it was failing.
Magnetars, like all neutron stars, spin incredibly fast and with precision. This particular magnetar had a rotation period of just 3.9 seconds, which is pretty impressive when you consider that it weighs more than the sun but is packed into a ball only a few miles across. When magnetars fail, they suddenly change their rotation speed. This naturally releases an enormous amount of energy that could potentially drive a fast radio burst. Related: A messy black hole may have triggered the biggest explosion in the universe Despite the observational evidence that faults in magnetars lead to the appearance of FRBs, scientists have not yet been able to discover the precise mechanism behind the phenomenon, although various ideas have been proposed. In a paper published May 25 in the journal Monthly Notices of the Royal Astronomical Society, a team of researchers suggested a startling scenario: They think that when a magnetar releases an FRB, we’re watching the death throes of an asteroid being torn apart.
The scenario goes like this. A random iron-rich asteroid passes too close to a magnetar. The intense gravity of the magnetar then breaks the asteroid into thousands of pieces. Some of those pieces then go into orbit around the magnetar, which affects the dead star’s angular momentum, changing its spin rate and causing a fault. The remaining pieces of the asteroid fall from their orbit and begin to make their way to the surface of the magnetar. As they do so, they pass through the region of the magnetar’s strongest magnetic fields. Because asteroids are rich in iron, they have a lot of electrical charges. The interaction of electrical charges moving at high speed through these incredibly strong magnetic fields leads to the formation of radiation. It is this radiation that we see as a rapid radio burst.
This scenario is appealing because astronomers have also seen FRBs associated with anti-failures, which occur when a magnetar’s spin slows suddenly. This newly proposed scenario can also explain anti-failure. All that is needed is for the asteroid to move in the opposite direction of the spin of the magnetar when it breaks up.