FAST radio bursts (FRBs) are mysterious, milliseconds-long showers of radio waves that come from unidentified objects outside our galaxy. About 60 FRBs have been identified to date, the strangest being a lone, repeating source. Now, it is no longer alone.
In August 2018, researchers at the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope in British Columbia, detected 13 more FRBs to add to the catalogue. One of them is the second FRB ever seen to repeat (Nature, , ).
The first one, called FRB 121102, was detected in November 2012. Ideas about what creates its pulses include everything from black holes to dark matter and even aliens. Now there is a second one – called FRB 180814 – we can compare the two. Finding any properties in common might help narrow down the likely source of FRB repeaters.
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Emily Petroff at the Netherlands Institute for Radio Astronomy says it was assumed that another repetitious burst of radio signals would eventually be found, but the similarities are still surprising.
Six bursts of radio waves emitted by FRB 180814 were detected between August and October 2018. At least two of the pulses had a structure that resembled some of those generated by FRB 121102. This included subpulses that started at a higher frequency, then cascaded down to lower and lower frequencies.
“We’ve seen that same structure in some of the pulses from 121102, but it has been observed at a higher frequency,” says Petroff. So, the two repeaters are singing the same song, but not the same notes. It is as if the two are part of a duet, with FRB 121102 singing soprano and FRB 180814 singing alto.
The research team, led by Cherry Ng at the University of Toronto, says these downward drifts in frequency are reminiscent of powerful radio bursts emitted by the sun. This same pattern may be present in all the FRB pulses, although we may currently lack the resolution to see it. Or it could be unique to the repeaters. That might be a clue to help sort out what is causing these extremely powerful bursts.
Knowing there is more than one repeating FRB means we are likely to find further ones. “In astronomy, one is an outlier, two is a population,” says Petroff. Hunting down that population requires looking at a large portion of the sky for a long time.
“Fast radio bursts have been linked to everything from black holes to dark matter and even aliens”
But that should be possible because the CHIME radio telescope’s field of view can capture large chunks of the northern sky in one go, meaning it sees the entire hemisphere for about 10 minutes each day.
“In the very first sky data, they managed to find 13 FRBs,” says Petroff. “That points to a really promising future where they’re going to find potentially hundreds, maybe thousands of FRBs per year.”
Most of the 13 new FRBs emitted scattered radio waves, meaning they had interacted with something in the past. The team analysed whether this type of signal was compatible with FRBs originating in the disc or spiral arms of large galaxies like ours, because some models suggest FRBs are made by young stars that would probably be in those spots.
But these simulations showed that the signals would need to pass through more matter to scatter as they did. This suggests that these FRBs may be located in dense environments such as inside a supernova remnant or near a supermassive black hole.
