This Unidentified Extragalactic Transmission Deepens the Fast Radio Burst Enigma

Fast radio bursts (FRBs) are among the coolest, weirdest things in the sky. Over the past 10 years, astronomers have bagged about two dozen of the events, which register as extreme anomalous spikes in radio telescope survey data. The first observed burst was captured at the Parkes radio telescope in Australia in 2001, but wasn't actually discovered until 2007, when an undergraduate student at West Virginia University noticed the strange spike while poring through archival radio data.

Given the high energy levels recorded, the bursts are almost certainly extragalactic in origin. They last for mere milliseconds and a crucial characteristic is that they don't repeat, leading to the assumption that they are the products of discrete events rather than ongoing "things," like stars.

A paper out today in Nature adds a new twist to things: One of the supposed bursts, FRB 121102, turns out to be repeating after all. This would ordinarily disqualify it from FRB status, but so far astronomers don't have an alternative explanation for the detections. While the FRB was detected in 2014 as a single burst, the group behind the new research offers follow-up observations from the William E Gordon Telescope at the Arecibo Observatory adding 10 more events.

While the bursts are all different from one another, each registering with a unique "spectral shape," the researchers are almost certain that they come from the same source. Moreover, it's likely that there exist more, weaker bursts with the same origin yet to be found.

It's thought that FRBs each originate in single cataclysmic events in space, with many different sorts of cosmic events capable of giving birth to a FRB. Just last week a study was published tracing one known burst back to a likely beginning in the collision of two neutron stars in a galaxy some six billion light-years away. The dispersion measures (DMs) and positions of the new bursts show that not only do they indeed have the same source, but that the source of FRB 121102 survived whatever epic event triggered the bursts in the first place.

As for what, specifically, that source may be, here's what the authors have to say: "Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star."

This is somewhat of a process of elimination. Unfortunately, while the bursts repeat, they're not periodic in any meaningful way, e.g. there aren't any discernible patterns in the durations between bursts. A galactic flare star is out as a potential source because this would imply some variation in the dispersion measures of the bursts, and the bursts of FRB 121102 are all about the same. Cataclysmic events like merging neutron stars or collapsing super-massive neutron stars are out too.

One possibility is that FRBs might trace back to planets orbiting within a magnetized pulsar wind where the planets might occasionally align in such a way to allow gusts of high-energy radio waves to erupt out of the system. But that doesn't work either because the bursts of 121102 are too quick to match any planetary orbital period. Another proposed FRB source is flares from magnetars, neutron stars boasting extremely powerful magnetic fields. That doesn't quite work either because no magnetar has ever been observed to emit more than a single flare over the four decades we've been looking for them.

So, FRB 121102 remains a mystery among a class of mysterious cosmic phenomena. Not to worry: We've only been studying these things for less than a decade.