Astronomers unveil new and bewildering characteristics of mysterious fast radio bursts

Artistic conception of the spherical radio telescope with an aperture of five hundred meters (FAST) in China. Credit: Jingchuan Yu

Fast radio bursts (FRBs) are millisecond-long cosmic bursts that each produce energy equivalent to the sun’s annual output. More than 15 years after the discovery of deep-space pulses of electromagnetic radio waves, their bewildering nature continues to surprise scientists, and the newly published research only delves into the mystery surrounding them.

In the September 21 issue of the magazine Natureunexpected new observations from a series of fast cosmic radio bursts by an international team of scientists, including UNLV astrophysicist Bing Zhang, question the prevailing understanding of the physical nature and core engine of FRBs.

The cosmic observations of the FRB were made in late spring 2021 using the massive five-hundred-meter spherical radio telescope (FAST) in China. The team, led by Heng Xu, Kejia Lee, Subo Dong of Peking University and Weiwei Zhu of the National Astronomical Observatories of China, along with Zhang, detected 1,863 flashes in 82 hours in 54 days from an active fast radio burst source. call FRB 20201124A.

“This is the largest sample of FRB data with polarization information from a single source,” said Lee.

Recent observations of a fast radio explosion from our Milky Way galaxy suggest that it originated from a magnetar, which is a dense city-sized neutron star with an incredibly powerful magnetic field. The origin of the very distant fast cosmological radio bursts, on the other hand, remains unknown. And the latest observations leave scientists questioning what they thought they knew about them.

“These observations brought us back to the drawing board,” said Zhang, who is also the founding director of UNLV’s Nevada Center for Astrophysics. “It is clear that FRBs are more mysterious than we have imagined. More multi-wavelength observation campaigns are needed to further unravel the nature of these objects.”

What makes the latest observations surprising for scientists are the irregular and short-lived variations of the so-called “Faraday rotation measure”, which is the magnetic field strength and particle density in the vicinity of the FRB source. The variations increased and decreased during the first 36 days of observation and stopped abruptly in the last 18 days before the source went extinct.

“I would compare it to making a film about the surroundings of an FRB source, and our film revealed a complex, dynamically evolving magnetized environment that had never been imagined before,” said Zhang. “Such an environment is not directly intended for an isolated magnetar. Something else could be in the vicinity of the FRB motor, perhaps a binary companion,” added Zhang.

To observe the FRB’s host galaxy, the team also used the 10-meter Keck telescopes located at Mauna Kea in Hawaii. Zhang says young magnetars are believed to reside in active star-forming regions of a star-forming galaxy, but the optical image of the host galaxy shows that, unexpectedly, the host galaxy is a metal-rich barred spiral galaxy like the our Milky Way. The location of the FRB is in a region where there is no significant star-forming activity.

“This position is inconsistent with a young magnetar core motor formed during an extreme explosion such as a long gamma-ray burst or superluminous supernova, widely hypothesized progenitors of active FRB motors,” Dong said.

The study, “A fast radio burst source at a complex magnetized site in a barred galaxy”, appeared on September 21 in the journal Nature and includes 74 co-authors from 30 institutions. In addition to the UNLV, Peking University and the National Astronomical Observatories of China, the collaborating institutions also include Purple Mountain Observatory, Yunnan University, UC Berkeley, Caltech, Princeton University, University of Hawaii and other institutions of China, United States , Australia, Germany and Israel.

Astronomers uncover clues that unravel the mystery of fast radio bursts

More information:
H. Xu et al, A fast radio burst source in a complex magnetized site in a barred galaxy, Nature (2022). DOI: 10.1038 / s41586-022-05071-8

Provided by the University of Nevada, Las Vegas

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