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Fast radio bursts are one of the most puzzling phenomena in
astrophysics. But a new discovery of eight new sources for them might help
scientists figure out what’s causing these intense outbursts of energy coming
from distant galaxies.
The newly discovered bursts are from repeating sources,
meaning they were observed to burst multiple times. Previously, only two
repeating fast radio bursts had been observed. The new observations suggest
that repeating bursts are more common than previously thought.
“It was certainly on the table that [repeaters] were pretty
uncommon and you weren’t going to see many of them,” said Deborah Good, paper
co-author and PhD student at the University of British Columbia. “Having
another eight sources is a good sign that it’s not terribly rare to have a
repeater.”
Fast radio bursts are intense flashes of electromagnetic
energy that last just fractions of a second. Finding repeaters is valuable to
understanding their nature. Currently, fast radio bursts, which originate
outside the Milky Way, are thought to be caused by some type of compact object
— like a neutron star, pulsar, or black hole — but scientists aren’t sure
exactly what mechanism drives the bursts.
“Anything you come up with for a model for fast radio bursts
needs to either explain why repeaters and one-offs are totally different
objects, or more likely needs to be able to easily explain the burst happening
again and again,” Good said.
The bursts were captured by the Canadian Hydrogen Intensity
Mapping Experiment, or CHIME for short, a telescope near Penticton in British
Columbia, Canada. The experiment continually maps the sky in radio frequencies,
typically observing the entire northern sky each day. The telescopes gather far
more information than can be analyzed or even stored, so automated computer
algorithms continually scan the data to look for interesting events.
The eight new events, reported in a new paper submitted to the
Astrophysical Journal Letters and published on the preprint site arXiv,
were seen in observations from August 2018 to March 2019 when CHIME was just
beginning its main science campaign.
After analyzing the data, the scientists noticed a unique structure
in the signal of some of the repeaters. Over the duration of the burst, the signal’s
frequency decreased slightly, similar to what had been seen in the two previous
repeaters. Why this happens, and if it’s something that’s unique to repeating
fast radio bursts, is still unclear.
“It may be the case that only repeaters have this structure,
but it’s not the case that all repeaters have that structure,” Good said. “It’s
still an open question.”
It’s possible a different source or mechanism is responsible
for the drifting signal in these repeaters but its still to early to say.
Within the scientific community there is still debate over whether one-off
sources are distinct or if they are simply repeaters that haven’t yet been
observed to repeat.
“We still
don’t have enough repeating fast radio bursts localized to host galaxies to say
something about either of [the leading] theories, but as we find more repeaters
and pinpoint their locations within their host galaxies, we will start to be
able to distinguish between different theories,” said Emily Petroff, astronomer
at the Anton Pannekoek Institute, University of Amsterdam, who was not
involved with the new study.