Fast radio bursts -- strange, sometimes repeating signals from the other side of the cosmos -- are really having a moment in 2020. The origins of the mysterious signals from deep space continue to puzzle scientists as they briefly and sporadically buzz the Earth. But as the numbers of FRBs discovered continue to stack up, astronomers are beginning to understand them a little more, and in May even used them to solve the universe's missing matter problem.
Although many bursts astronomers have detected are one-offs, a particular burst, known as FRB 180916.J0158+65, is particularly loud and constant, having been detected 38 times.
A study, published Wednesday in the journal Nature by researchers from the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) collaboration, detail the repeating bursts of FRB 180916.J0158+65 from September 2018 to February 2020. The burst has previously been localized to a spiral galaxy some 500 million light-years away, and the CHIME/FRB collaboration documented its unusual rhythm in a preprint paper in February.
Using the huge ground-based CHIME telescope, situated in British Columbia, researchers detected the deep space signals with a 16-day regularity. Over four days, they'd detect the radio bursts every hour or so, before the signals suddenly stopped. Then, after 12 days of silence, they'd kick back up again. The rhythm of the bursts seems to follow this pattern, but it's unusual in that there's no other FRBs yet discovered that cycle in the same way.
And that's good news!
"This is an amazing result because it gives us a whole new layer of insight into what can be making these repeating fast radio bursts," says Adam Deller, an astrophysicist at Swinburne University of Technology who was not affiliated with the study.
Repeating bursts offer the best chance to try to understand what might be causing FRBs because they give astronomers a second, third or 38th look at the signal. There are dozens of theories, but the source of the signals remains a mystery. One prominent theory is that FRBs are caused by magnetars, a type of neutron star with an extremely powerful magnetic field. These stars rotate on their axis and may emit beams of energy, but our current understanding of these cosmic beasts suggests they would spin too fast to have the periodicity observed in FRB 180916.J0158+65.
"The recent discovery of an immensely bright burst from a magnetar in our own galaxy was another big piece of the puzzle," says Deller. "It was the most similar thing we've yet seen from within our Milky Way."
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Another theory posits that they are just a regular, old neutron star with a focused radio beam that only occasionally sweeps across our field of view on Earth. Perhaps, even, a nearby black hole is disrupting the signal thanks to its huge gravitational pull. Astronomers still don't know.
Complicating matters the fact many of the detected ultra-powerful radio signals don't repeat. We hear them, and they disappear. With more repeaters being discovered, we edge closer to understanding their nature. In 2019, the CHIME collaboration discovered a new set of eight repeating bursts that can be used for follow-up analysis. It's hoped that by studying the repeating bursts, astronomers will be able to shed light on these mysterious signals.
More recently, a second repeating burst was found with an unusual periodicity. Its cycle seemed to work on a 157-day timeline -- 90 days of activity and 67 when it went silent.
Astronomers will need to keep their telescopes focused on repeating FRBs over long periods to pull apart exactly what they are. There's also a possibility that further investigation will reveal FRB 180916.J0158+65's unusual rhythm isn't a rhythm at all.
Very few repeating bursts have been localized to their home in the universe, and ASKAP, an Australian facility searching for FRBs, is "running overtime", according to Deller, to try and pinpoint which galaxies they came from. That will allow a better comparison between galaxies that host FRBs which repeat and those that don't.
Whatever the case -- and I know what you're thinking -- it's very, very unlikely to be aliens.
Discussing repeating bursts last year, Deller said, "I think in all likelihood we'll work out a natural explanation for these events, but I like to keep an open mind and follow wherever the evidence leads me.
This post originally appeared in February and has been updated now that the work has been peer-reviewed.