A odd signal from space occasionally reaches our scanners on Earth.
These incredibly brief signals, known as rapid radio bursts (FRBs), have a
millisecond period and can only be seen at radio frequencies.
However, they can release as much energy as 500 million Suns in those
milliseconds and at those frequencies, and the majority of them have never
been found again.
It's a bit of a riddle what they are and how they are produced. However, a
recent finding may indicate a previously unidentified process generating
these potent radiation bursts.
A brilliant, non-repeating rapid radio burst was captured by the Canadian
Hydrogen Intensity Mapping Experiment (CHIME) on April 25th, 2019. (
FRB).
Just 2.5 hours earlier, a binary neutron star impact that occurred as it
approached the unavoidable end of its decaying trajectory was captured by
the Laser Interferometer Gravitational-Wave Observatory (LIGO).
The FRB's position in the heavens coincided with the gravitational wave
event's plausible area and was located nearby. The possibility that the two
events were unrelated, a team of astronomers headed by Alexandra Moroianu of
the University of Western Australia has established, is exceedingly
tiny.
Only a small percentage of FRBs repeat, and the overwhelming majority of
them are one-off events, making it incredibly challenging to research
them.
Until recently, spotting one required luck—you had to be looking at the
correct area of the sky at the right moment. However, the number of
detections has grown to over 600 thanks to all-sky scans.
A significant development occurred in 2020 when a FRB was discovered for
the first time originating from within the Milky Way galaxy. It was
discovered that the phenomenon was caused by a particular kind of neutron
star called a magnetar, whose absurdly potent exterior magnetic field
battles with gravity to periodically cause the star to tremble and
flare.
Although malfunctioning magnetars offer one possible reason, we are unsure
if that is the whole story. FRBs have a wide range of characteristics,
suggesting that multiple mechanisms may be able to generate them.
Numerous hypotheses suggest a connection between FRBs and gravitational
waves, especially if neutron stars are involved, either during or after the
gravitational wave discovery.
Moroianu and her coworkers started browsing inventories as a result. For a
total of 171 FRB events, the
CHIME collection
of observations from July 2018 to July 2019 coincided with the LIGO-Virgo
observation period.
In order to find FRB events that happened within the LIGO-identified region
of the sky and were temporally near to gravitational wave detections, the
researchers cross-referenced these events with the
GWTC-2 database.
And they felt a powerful impact.
At 08:18:05 UTC on April 25, 2019, LIGO detected GW20190425. The area from
which the detection had arisen was constrained by the lack of a Virgo
detector detection. It was created by the merging of two neutron stars and
was thought to be 520 million light-years distant.
The same day, at 10:46:33 UTC, FRB20190425A was found, with a maximum
distance of 590 million light-years, within the region of the heavens LIGO
had identified as a likely cause of the neutron star merger.
They discovered that if the two weren't connected, this would be a strange
accident. The researchers determined that the likelihood of the two events
happening at the specified distances, during the discovery period, and
within the area of space specified by LIGO was only 0.00019.
The two occurrences most likely originated from a galaxy known as
UGC 10667, but further investigation may be necessary to determine how the FRB was
created.
The burst was thought to have been triggered, for the time being, by a
blitzar, a process suggested for FRBs
nearly ten years ago. When a neutron star's rotation decreases, the only thing that was keeping
it from collapsing into a black hole is its mass, which is too great to be
sustained by degeneracy pressure.
The collapse of a post-binary neutron star-merger magnetar is mentioned in
the GW, short gamma-ray burst (sGRB), and FRB association hypothesis, which
the
researchers claim
is consistent with the possible GW-FRB association.
The 2.5-hour delay time between the FRB and the GW event is the survival
time of the supramassive neutron star before collapsing into a black hole,
which is consistent with the expected range of the delay timescale for a
supramassive magnetar from both theory and observational data. This scenario
has been confirmed through numerical simulations.
The neutron stars in GW20190425 had masses that were considerably greater
than those of the majority of neutron star pairs found in the Milky Way. The
few recurring FRB sources can be explained by the fact that these lower mass
binaries would create more durable heavyweight neutron stars after merging,
which could live for a very long time and emit FRBs frequently.
The two occurrences may or may not have been connected, but one thing is
certain: the rate of binary neutron star mergers is believed to be much,
much lower than the rate at which FRBs like FRB190425A are discovered.
Therefore, this possible process is insufficient to explain the puzzling
signals that sputter across the radio heavens.
There is still room for more research. But the fact that we appear to be
getting closer to some solutions is incredibly thrilling.
The research has been published in
Nature Astronomy.
