Groundbreaking study reveals strong and changeable magnetic field surrounding repeating fast radio burst

Scientists discover a repeating fast radio burst (FRB) that never stops, surrounded by a highly changeable magnetic field.
Kavita Verma
An illustration of radio signal
An illustration of radio signal


Since its discovery in 2007, fast radio bursts (FRBs) have baffled astronomers. FRBs are powerful, millisecond-long radio bursts from space that produces as much energy during their brief existence as the Sun produces over a few days. Very little is known about what or how most FRBs are produced; most come from outside our Milky Way galaxy. However, one FRB that has never stopped repeating has been highlighted by a NEW study recently published in Science.

Using the five-hundred-meter Aperture Spherical Radio Telescope (FAST) in China, astronomers identified the repeated burst in 2022 as FRB 20190520B. FRB 20190520B, which produces radio bursts a few times an hour, occasionally at different radio frequencies, is the rarest repeating FRB of all. Astronomers hurried to extend the original study using additional radio frequencies after discovering this exciting phenomenon.

Powerful magnetic fields surrounding the burst

Further research revealed that FRB 20190520B is located in a 3.9 billion light-year-distance dwarf galaxy, home to an incredibly dense environment. The FRB source is surrounded by substances that emit powerful, long-lasting radio waves. The exploding source was speculated to be a young neutron star in a complex environment as a result of this.

The burst emits potent signals at relatively high radio frequencies, according to observations of FRB 20190520B made with the CSIRO Parkes radio telescope in New South Wales, the Green Bank Telescope in the United States, and the Murriyang radio telescope in Australia. The electromagnetic waves in these high-frequency transmissions turned out to be highly polarized, which means they are "waving" in one direction considerably more powerfully than in others.

Different frequencies cause this polarization to shift in direction, and monitoring how much it varies lets us know how strong the magnetic field was when the signal passed through. This polarization measurement indicates a highly magnetized environment surrounding FRB 20190520B. Additionally, throughout the 16 months that astronomers monitored the source, the magnetic field's strength appeared to change and even reverse directions twice. The magnetic field's direction around an FRB has never been seen to alter.

Binary System Hypothesis

Recent observations of recurrent FRBs are most commonly explained by binary systems, consisting of a neutron star and another massive star or a black hole. The most recent findings support the concept involving a big star. However, other possibilities cannot yet be ruled out. Strong stellar winds and well-organized magnetic fields are known to surround massive stars. A reversal is anticipated in the direction of the magnetic field direction if the source of the bursts were going in and out of the stellar wind region as it moved through its orbit. This explanation is supported by the timing of the magnetic field reversal, the observed variability in the apparent field strength, and the concentrated plasma surrounding the burst source.

Study Abstract:

Fast radio bursts (FRBs) are brief, intense flashes of radio waves from unidentified extragalactic sources. Polarized FRBs originate in highly magnetized environments. We report observations of the repeating FRB 20190520B spanning 17 months, which show that the FRB’s Faraday rotation is highly variable and twice changes sign. The FRB also depolarizes below radio frequencies of about 1 to 3 gigahertz. We interpret these properties as being due to changes in the parallel component of the magnetic field integrated along the line of sight, including reversing direction of the field. This could result from propagation through a turbulent magnetized screen of plasma, located 10–5 to 100 parsecs from the FRB source. This is consistent with the bursts passing through the stellar wind of a binary companion of the FRB source.

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