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More than 15 years after the discovery of fast radio bursts, new research has shed light on and deepened the mystery of the sources of these deep space phenomena.
Fast radio bursts, or FRBs, are bright, powerful radio waves that last from a fraction of a millisecond to a few milliseconds, each producing energy equivalent to the sun’s annual output.
Recent studies have suggested that some FRBs originate from magnetars, which are neutron stars with very strong magnetic fields. A fast radio burst found in the Milky Way was linked to a magnetar, according to a 2020 study.
But scientists have yet to determine the origin of cosmological FRBs, which are billions of light-years away. An international team of scientists set out to see what they could learn from observations of nearly 1,900 bursts from an active radio burst source outside our galaxy called FRB 20201124A, according to a study published Sept. 21 in the journal Nature.
The outbursts associated with FRB 20201124A occurred over 82 hours and 54 days in the spring of 2021, making it one of the most well-known radio bursts. It was observed through the world’s largest radio telescope: the China-based Five Hundred Meter Aperture Spherical Radio Telescope, or FAST.
During the first 36 days, the study team was surprised by the irregular and short-lived changes in the Faraday rotation measure, which measures the magnetic field strength and particle density around FRB 20201124A. A larger rotation measure means the magnetic field near the source of the radio burst is stronger, denser, or both, while a smaller measure means the opposite, Bing Zhang, an astrophysicist and co-author of the study, said by email.
“This is not a reflection of the beginning of the FRB[lifetime],” said Zhang, founding director of the Center for Astrophysics at the University of Nevada, Las Vegas. “The FRB source has been around for a long time, but has mostly been dormant. It wakes up from time to time (this time for 54 days) and emits many explosions.’
The measurements went up and down during this time period, then stopped in the last 18 days before the FRB damped off – “suggesting that the strength and/or density of the magnetic field in the line-of-sight around the FRB source is changing with time,” Zhang added. “It suggests that the environment of the FRB source is dynamically evolving, with rapidly changing magnetic fields or densities, or both.”
“I liken it to shooting a movie around an FRB source, and our movie revealed a complex, dynamically evolving, magnetized environment that had never been imagined,” Zhang said in a news release.
A physical model built by a team of researchers based on observations of FRB 20201124A proposes that the FRB came from a binary system 8,480 light-years away that contained a magnetar and a Be star, which is hotter, larger, and spinning faster than a star. the sun, according to a separate study published on September 21 in the journal Nature Communications.
The complex, magnetized environment of the radio burst is within one astronomical unit (the distance between the Earth and the sun) of the source, the researchers found.
They also discovered that the burst originated from a barred spiral galaxy, which is rich in metals and about the size of the Milky Way, using the 10-meter Keck telescopes on Mauna Kea, Hawaii. The source of the radio burst is located between the galaxy’s spiral arms, where no significant star formation occurs, and so it is likely to be of magnetar origin only, according to Nature study author Subo Dong, an associate professor at the Kavli Institute for Astronomy and Astrophysics. at Peking University.
“Such an environment is not directly expected for an isolated magnetar,” Zhang said in a news release. “Something else could be around the FRB engine, perhaps a binary companion.”
Model analysis should encourage the authors to further search for fast radio burst signals from Be star/X-ray binaries.
“These observations took us back to the drawing board,” Zhang said. “It is clear that FRBs are more mysterious than we have imagined. More multi-wavelength observation campaigns are needed to reveal more about the nature of these objects.’