A strange FRB in a strange place

Fast radio bursts, or FRBs, are brief, intense flashes of radio waves believed to arise on extremely magnetic neutron stars called magnetars. One-off bursts are difficult to trace, but a few repeat, allowing researchers to more easily determine their origin. That’s exactly what a team studying one repeater, called FRB 20200120E, accomplished — with unexpected results. Their work was published Feb. 23 in Nature and Nature Astronomy.

Bursts from FRB 20200120E are as short as 60 billionths of a second. That indicates they are coming from “a tiny volume in space, smaller than a soccer pitch,” said team co-leader Kenzie Nimmo of the Netherlands Institute for Radio Astronomy (ASTRON) and the University of Amsterdam in a press release. The fact that the signal originates from such a small area supports the idea that FRBs come from magnetars, as neutron stars themselves are small: roughly the size of Manhattan.

Using several radio telescopes, the team tracked FRB 20200120E to its origin. It lies in M81, just 12 million light-years away. That makes it the closest FRB to date. Even odder, the FRB is in a dense grouping of old stars called a globular cluster. Finding a magnetar — the product of short-lived stars — in this environment is unexpected, the team said. All other FRBs with known positions lie in regions of distant galaxies that house young, massive stars.

So, how did the magnetar powering FRB 20200120E form in such an unexpected place? There are two possibilities: first, a long-predicted but never-before-seen phenomenon called accretion-induced collapse.

This is when a white dwarf pulls mass from a companion and tips over a cosmic weight limit, collapsing into a denser neutron star. Although posited to be rare in globular clusters, it’s the simplest and likeliest explanation, the team says. Alternatively, perhaps FRB 20200120E is the result of a merger between two white dwarfs, two neutron stars, or one of each. Such mergers are more common in globular clusters and could create a neutron star.

For now, the mystery remains. And regardless of the answer, it indicates there are likely many ways to create the magnetars that power these strange signals.

ASTRON/DANIËLLE FUTSELAAR, ARTSOURCE.NL MYSTERIOUS ORIGINS. Researchers have traced a fast radio burst to a globular cluster full of old stars in a nearby galaxy. But the magnetars believed responsible for FRBs are young, raising questions of how it could have gotten there.