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Rarely sighted and unusually bright, fast radio bursts keep throwing out mysterious signals that can't be explained by existing theories, sending astrophysicists in new directions as they search for their sources.
Some blip more than once, drawing researchers back for repeat investigations. Most are never heard from again. A new look at those one-hit-wonders is prompting astrophysicists to once again rethink what they are and where they originate from.
The new tranche of data comes from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope that surveys large swathes of the sky rather than restricting its focus on small patches near previously detected fast radio bursts (FRBs).
In 2020, CHIME detected the first FRB known to repeat in a distinct and repeatable fashion, on a 16-day loop. Today, just 3 percent of known FRBs emit flashes more than once, with most emitting energetic flashes in unpredictable, erratic patterns.
The vast majority of the more than 1,000 FRBs cataloged so far are non-repeaters: solitary blasts of radio waves mere milliseconds in duration, that are as powerful as hundreds of millions of Suns.
Finding differences between these two types of blast could point to a mutual origin story.
"This was the first look at the other 97 percent," says Ayush Pandhi, an astrophysics graduate student at the University of Toronto who led the new study.
Pandhi and colleagues looked at the burst profiles of FRBs, specifically the orientations of the waves in what is referred to as their polarization.
Of the 128 non-repeating FRBs studied, 118 had polarization information collected. Of those, 89 met the criteria for being considered polarized, tripling the total number of known FRB sources with known polarization properties.
Comparing these findings to studies that examined polarization in repeating FRBs prompted the team to "reconsider what we think FRBs are and see how repeating and non-repeating FRBs may be different," Pandhi says.
Catching rays of polarized light direct from a source is thought to indicate the presence of extremely powerful magnetic fields.
On the other hand, evidence from repeating FRBs suggests that a lack of polarization may relate to the scattering of emissions as they blast through materials around the source.
"This is a new way to analyze the data we have on FRBs. Instead of just looking at how bright something is, we're also looking at the angle of the light's vibrating electromagnetic waves," explains Pandhi.
"It gives you additional information about how and where that light is produced, and what it has passed through on its journey to us over many millions of light years."
The results suggest this sample of non-repeating FRBs is quite different to repeating FRBs, and may have originated in a less extreme environment with a lower burst rate. The researchers also think that the cause of the polarization from non-repeating FRBs is "likely intrinsic" to how these brief and blinding bursts of radio waves are generated, distinct from whatever causes scattering around prolific repeaters.
First discovered in 2007, this is not the first time that surprise signals have prompted astrophysicists to rethink their understanding of FRBs, including how and where they form.
In January, researchers tracked down the origin of the most powerful, furthest-traveling FRB ever to reach us to a tightly-knitted group of seven galaxies.
Before this, pulsars and a type of neutron star called magnetars were the main suspects, their emissions thought to interact with the whirling winds of dense, magnetized plasma ejected from nearby stars or black holes.
So varied are the suspected sources, frequencies, and properties of known FRBs that these bizarre blips have spawned 48 separate theories and counting.
Even if after this new study our understanding of FRBs remains a little fuzzy, at least we're expanding our view of them.
The study has been published in The Astrophysical Journal.
