A fast radio burst is a bright flash of radio energy that is unresolved (point-like), widely spread (spanning a broad band of radio frequencies), and millisecond in duration. What causes them is one of the greatest mysteries in modern-day astronomy.
According to new research by an international team of scientists, deep-space fast radio bursts originate from an evolving, magnetized environment. This evidence contradicts current theories of what causes them. The fast radio burst (FRB) is a type of cosmic explosion that lasts around a millisecond. According to scientists, an average FRB releases the same amount of energy as the Sun does in 3 days. Duncan Lorimer and David Narkevic discovered the first FRB in 2007 while studying archival pulsar survey data. There have been many recorded FRBs since then, including several that appear to repeat in an irregular manner. There is nevertheless one FRB that repeats in a regular manner: FRB 180916 pulses every 16.35 days. The CHIME radio telescope detected the first Milky Way FRB in April 2020, but most of them are extragalactic. Over 500 FRBs from outer space were detected in June 2021, according to astronomers.
The exact origin of what FRBs are remains a mystery, and scientists continue to be puzzled by the deep-space pulses of electromagnetic radio waves after they were discovered more than 15 years ago – and the latest research only deepens their mystery. An international team of scientists – including UNLV astrophysicist Bing Zhang – published a series of unexpected new observations in Nature on Sept. 21 regarding cosmic radio bursts. These observations challenge prevailing theories about their nature and central engine.
The Chinese FAST (Five-hundred-meter Aperture Spherical Radio Telescope) was used to observe cosmic FRBs in late spring 2021. In 82 hours over 54 days, researchers led by Heng Xu, Kejia Lee, Subo Dong, and Weiwei Zhu from Peking University and the National Astronomical Observatory of China detected 1,863 bursts from FRB source 20201124A. Lee noted that this is the largest sample of FRB data with polarization information from a single source. The Milky Way galaxy recently experienced an incredibly fast radio burst, which may have come from a magnetar. A magnetar is a dense, city-sized neutron star with an extremely powerful magnetic field. Fast radio bursts from very distant galaxies, however, are unknown in origin. These findings challenge what scientists believed they knew about these mysterious pulses.
Back to basics
Zhang, who oversees UNLV’s Nevada Center for Astrophysics, said, “These observations brought us back to the drawing board.” FRBs appear to be far more mysterious than we anticipated, he revealed. “More multi-wavelength observational campaigns are needed to unveil the nature of these objects further.” Recent observations of FRBs have surprised scientists because they indicate irregular, short-term variations in the “Faraday rotation measure,” which represents the strength of the magnetic field and particle density close to the source. Within the first 36 days of observation, the variations went up and down and suddenly stopped during the last 18 days.
“I see it as filming a movie of the surroundings of an FRB source, and our film revealed a complex, dynamically expanding, a magnetized environment that was never contemplated before,” Zhang explained in a statement by the University of Nevada. “Such an environment is not straightforwardly expected for an isolated magnetar. Something else might be in the vicinity of the FRB source, possibly a binary companion,” added Zhang. A 10-m Keck telescope at Mauna Kea was used to observe the host galaxy of the FRB. According to Zhang, young magnetars reside in star-forming regions of a galaxy, but observing the galaxy optically reveals that it resembles our Milky Way, which is a metal-rich spiral galaxy. There are no significant activities associated with star formation at the location of the FRB.
“This location is inconsistent with a young magnetar central engine formed during an extreme explosion such as a long gamma-ray burst or a superluminous supernova, widely speculated progenitors of active FRB engines,” said Dong.
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