One of the most defining characteristics of the mysterious deep-space signals we call fast radio bursts is that they're unpredictable.
For the first time, astronomers have now found a fast radio burst (FRB), which repeats on a regular cycle.
Every 16.35 days, the signal called FRB 180916.J0158+65 follows a similar pattern. For four days, it'll spit out a burst or two every hour. It then falls silent for 12 days. Then the whole thing repeats.
Astronomers, along with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Collaboration in Canada, watched this cycle for a total of 409 days. We do not yet know what that means; but it could be another piece in the complex conundrum of FRBs.
It is easy to become a bit obsessed with fast radio bursts, an exciting space mystery that has defied any attempts at a comprehensive explanation so far.
FRBs are largely energetic flares of radiation in the radio spectrum, which last only some milliseconds at most. In this timeframe, they can discharge as much power as hundreds of millions of Suns.
The majority of them spark once, and we've never detected them again. That makes it quite hard to track these bursts down to a source galaxy. Several FRBs spit out repeating radio flares, but wildly unpredictable. Those are easier to track to a galaxy, but so far, that hasn't brought us a great deal closer to an explanation.
In 2019, the CHIME collaboration announced that they had detected eight new repeating fast radio bursts, bringing the then-total of repeaters to ten out of more than 150 FRB sources.
FRB 180916.J0158+65 was one of the eight repeaters included in 2019's haul; apart from its repeat bursts, initially it did not seem to be anything special. However, as the CHIME experiment continued to stare at the sky, a pattern emerged.
That offers new information that can be used to try and model what could be causing FRB 180916.J0158+65.
Other objects which demonstrate periodicity are usually binary systems - stars and black holes.
FRB 180916.J0158+65 is one among the handfuls of FRBs that have been traced back to a galaxy. It is on the outskirts of a spiral galaxy 500 million light-years away, a star-forming region. A supermassive black hole is unlikely, yet a stellar-mass black hole is possible.
It also cannot be ruled out that the FRB source is a single, lone object such as a magnetar or X-ray pulsar, although the researchers note this explanation is a little harder to reconcile with the data. This is because these objects have a wobbling rotation that produces periodicity, and none are known to wobble that slowly.
And radio pulsars that do have periodic intervals of several days are orders of magnitude fainter than FRBs. So it's still a mystery.
However, remember that the 11th repeater we mentioned earlier? It was found coming from an FRB that astronomers had thought was a one-off; its repeats were merely too faint for the equipment which had initially been used to look for them.
That also suggests that many more FRBs could be repeating, yet outside our detection range. And the fact that FRB 180916.J0158+65 seemed more or less the same as other FRBs could mean that other repeating FRBs are also on a cycle - we've just not detected those cycles yet.
Therefore, the next step would be to continue staring at FRB 180916.J0158+65 for a bit. However, it also would be pretty interesting to try and see if periodicity can be detected in other bursts as well.
The research is available on arXiv.
COMMENTS