Gravitational waves could give us insight into fast radio bursts

Fast radio bursts are a mysterious phenomenon that astronomers discovered only in the XXI century. There are still debates about their source. However, scientists hope to find out the truth soon thanks to gravitational waves, because these short-lived events are believed to be associated with neutron stars and black holes.

Neutron star. Source: phys.org

Mystery of the fast radio bursts

Fast radio bursts (FRBs) are mysterious pulses of energy that can last from a fraction of a millisecond to three seconds. Most come from outside the galaxy, although one has been detected from a source inside the Milky Way. Some of them are also repetitive, which only adds to their mystique.

Although astrophysicists believe that a high-energy astrophysical process is the likely source of FRBs, they are not sure how they are generated. Researchers used gravitational waves (GWs) to observe one of the known sources of FRBs to try to better understand them.

The only confirmed source of FRBs in the Milky Way is a neutron star with a strong magnetic field, a magnetar called SGR 1935+2154. Its FRB was discovered in 2020 and was the first to be associated with a source. Although SGR 1935+2154 is about 20,000 light-years away, it is still close enough to be studied.

In a new study published in The Astrophysical Journal, scientists used the British-German GEO600 gravitational wave detector to investigate any ties between FRBs and gravitational waves. The study is titled “A Search Using GEO600 for Gravitational Waves Coincident with Fast Radio Bursts from SGR 1935+2154” and its lead author is A.G. Abac of the Max Planck Institute for Gravitational Physics.

FRB and magnetars connection

FRBs are extremely energetic as well as magnetars. Establishing a connection between the FRB and the SGR 1935-2154 magnetar is a major step in understanding these phenomena, although there remain a number of unanswered questions. Some magnetars repeatedly produce flares and also glow in X-rays.

Magnetars can experience powerful stellar earthquakes when the stress in their crust is released, and the released energy shakes the magnetar’s magnetic field, releasing FRBs and X-rays. Researchers wonder if the same earthquakes could generate gravitational waves.

“Observing fast radio bursts and gravitational waves from a magnetar at almost simultaneously would be the evidence we have been looking for for a long time,” said James Lough, lead scientist of the German-British gravitational wave detector GEO600 at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hanover.

Simultaneous FRB and GWs observations could confirm the common origin of neutron star-generated stellar earthquakes. If the magnetar generates GWs, they will be strong when they reach our detectors, and their effects will be easier to observe. Between April 2020 and October 2022, SGR 1935+2154 generated three FRB episodes, and GEO600 listened to them. The GWs detector is part of a global network of gravitational wave detectors.

Searching for gravitational waves

“It was essential that GEO600 could continue observing while all the other detectors were in an upgrade phase,” explained Lough. “Otherwise, we would have missed the opportunity of having gravitational-wave data during these fascinating events occurring so close to us.”

Unfortunately, careful analysis of the GEO600 data found no evidence of gravitational waves. However, the observations of the detector were still valuable. Because the magnetar is so close to us, even the lack of detection provided some new information.

This is not the first time scientists have used GW detectors to search for them, emitted simultaneously with FRBs as well as GWs from magnetar starbursts and pulsar disruptions. Various researchers have tried unsuccessfully to find them with the more powerful LIGO, Virgo, and KAGRA (LVK) unions.

The LVK detectors are larger and more powerful than GEO600. Their data show that the maximum possible gravitational wave energy that could be emitted during the FRB of a magnetar in 2020-2022 and not be detected must have been up to 10,000 times smaller than what astronomers have concluded from previous studies.

Different models explain how GWs form in FRBs, and their observations are not yet sensitive enough to distinguish them. However, by setting limits to the strength of GWs, GW observations still provide information that helps scientists improve their models.

The attempt to link GWs and FRBs is really just beginning. Although LIGO/Virgo was unable to observe the magnetar during the last FRB, hopefully they will work during the next episode. This time their efficiency and sensitivity will be enhanced.

According to phys.org

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