(ORDO NEWS) — From time to time our detectors here on Earth get a strange signal from outer space.
These signals, known as fast radio bursts (FRBs), are very short, only milliseconds long, and are only detectable in the radio spectrum.
However, in those milliseconds and at these wavelengths, they can emit as much energy as 500 million suns, and most of them have never been detected again.
What they are and how they are generated remains an enigmatic mystery. But the new discovery could point to a previously unknown mechanism behind these massive bursts of radiation.
On April 25, 2019, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) recorded a bright, non-repeating fast radio burst (FRB).
Just 2.5 hours ago, the Laser Interferometric Gravitational Wave Observatory (LIGO) detected a gravitational wave event, the collision of a binary neutron star with the inevitable end of its decaying orbit.
The position of the FRB in the sky fell into the reliable region of the gravitational wave event and from the same distance.
A team of astronomers led by Alexandra Moroianu of the University of Western Australia has determined that the chances that the two events are unrelated is extremely low.
Bursts are extremely mysterious; only a few of them are repeated, and the singular nature of the vast majority makes them extremely difficult to study.
Previously, their discovery was accidental; it was necessary to study the right section of the sky at the right time to catch it. However, all-sky surveys increased the number of detections to over 600.
A breakthrough came in 2020: FRBs were first detected coming from the Milky Way galaxy.
This has been traced back to a type of neutron star called a magnetar, whose insanely powerful external magnetic field struggles with internal gravity, causing the star to shake and flare from time to time, we don’t know if this is the full picture.
FRBs vary quite a lot, and it is likely that there is more than one mechanism that can produce them.
There are several theories that predict a relationship between FRBs and gravitational waves, especially if neutron stars are involved, either during or after the detection of gravitational waves.
Therefore, Moroyanu and her colleagues went to look in the catalogs. The CHIME observing catalog from July 2018 to July 2019 overlaps with the LIGO-Virgo observing cycle, with a total of 171 FRB events.
The researchers matched these events with the GWTC-2 catalog by looking for FRB events that occurred in time close to the detection of gravitational waves, within the region of the sky identified by LIGO.
GW20190425 was observed by LIGO on April 25, 2019 at 08:18:05 UTC. The lack of detection by the Virgo detector helped limit the area from which the detection originated.
It was estimated to be about 520 million light-years away. It was formed as a result of the merger of two neutron stars.
FRB20190425A was detected on the same day, at 10:46:33 UTC, within the range of the sky that LIGO put forward as a likely source of neutron star mergers, and with an upper distance limit of 590 million light years.
This, they discovered, would be an uncanny coincidence if they weren’t connected. The researchers calculated that there is only a 0.00019 chance that two events will occur at the specified distances, within the detection time, and in the region of space defined by LIGO.
These two events likely originated in a galaxy called UGC 10667, but the mechanism that created the FRB may require further analysis.
For now, the team believes the spike was caused by a blitzar, a mechanism proposed for FRB nearly a decade ago.
This is when a neutron star, too massive to be supported by the pressure of degeneracy, collapses into a black hole as its rotation slows down – the only thing that prevents this collapse.
“While we cannot definitively define a potential GW FRB association with a unified theory, it is consistent with GW, short gamma-ray burst (sGRB) and the FRB association theory that causes neutron star merger magnetar collapse,” the researchers write.
“The FRB generation mechanism is the so-called blitz mechanism, which has been confirmed by numerical simulations.
In this scenario, the 2.5-hour delay between the FRB and the GW event is the survival time of a supermassive neutron star.
Before collapsing into a black hole, which is consistent with the expected delay time scale range for a supermassive magnetar both in theory and observational data.”
The masses of the neutron stars of GW20190425 were significantly higher than those of most double neutron stars found in the Milky Way.
These lower-mass binaries would produce more stable heavy-weight neutron stars after merging, which could exist for a long time and repeatedly emit FRBs, which would explain the multiple recurring sources of FRBs.
Whether the two events were related or not. has yet to be confirmed, but one thing is certain: the estimated rate of binary neutron star mergers is much, much slower than the rate at which FRBs such as FRB190425A are detected.
Thus, this potential mechanism cannot by itself explain the mysterious signals that fly across the radio sky.
Further research is still needed. But that we seem to be getting closer to some answers is extremely interesting.
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