An international team of astronomers has identified evidence suggesting that at least some fast radio bursts (FRBs) originate from binary stellar systems. This conclusion follows observations of the repeating FRB 20220529 using China's Five-hundred-meter Aperture Spherical Telescope (FAST). Researchers detected a significant and temporary change in the FRB's magnetic environment, which they interpret as a dense plasma cloud, potentially a coronal mass ejection from a companion star, briefly passing through the line of sight. These findings contribute to understanding the origins of these energetic cosmic signals.
Understanding Fast Radio Bursts
Fast radio bursts are millisecond-long, powerful radio flashes that originate from beyond the Milky Way galaxy. Discovered in 2007, these transient phenomena release energy equivalent to the Sun's total radiation over a week. While most FRBs are single occurrences, a small number repeat, allowing for long-term study. The precise mechanisms behind their generation and whether they involve companion objects have been subjects of ongoing research. Proposed models often involve neutron stars or magnetars, which are neutron stars with extremely strong magnetic fields.
Observation of FRB 20220529
The research team, which included astronomers from The University of Hong Kong (HKU) and the Purple Mountain Observatory (PMO) of the Chinese Academy of Sciences (CAS), used the FAST telescope in Guizhou, China, to continuously monitor the active repeating FRB 20220529. This source is located approximately 2.9 billion light-years from Earth and is considered intrinsically faint, making its bursts challenging to detect with other facilities. Monitoring commenced in June 2022.
During their observations, scientists tracked the Faraday Rotation Measure (RM), a parameter indicating the properties of magnetized plasma along the signal path from the FRB source to Earth. For the initial 18 months, FRB 20220529's RM showed minor fluctuations.
Detection of an "RM Flare"
In December 2023, the team recorded a significant event: the RM suddenly increased to approximately 20 times its average variability. This surge was followed by a gradual decline, with the RM returning to its typical fluctuation range within two weeks. This rapid and reversible change in the magnetic environment represents the first such record obtained in FRB research and has been termed an "RM flare."
Interpretation and Implications
Researchers interpret this phenomenon as a dense, magnetized plasma cloud briefly passing through the line of sight between the FRB source and Earth. Professor Yuanpei Yang noted that the characteristics of this plasma clump are consistent with coronal mass ejections (CMEs) observed from the Sun and other stars.
According to Wu Xuefeng, deputy director of the PMO, existing theories are challenged to explain the observed RM flare if FRB 20220529 originated from an isolated neutron star. In contrast, within a binary system, violent activities from a companion star or the specific geometric structure of the binary orbit could naturally produce the observed phenomenon by sending plasma clouds into the line of sight. Professor Bing Zhang suggested that this discovery provides a clue to the origin of at least some repeating FRBs, indicating a binary system potentially comprising a magnetar and a star comparable to our Sun.
This finding supports a recent theoretical framework proposing that all FRBs originate from magnetars, with interactions within binary systems facilitating a specific geometry that allows for more frequent, repeating bursts. Duncan Lorimer, a professor of Physics and Astronomy at West Virginia University, highlighted FAST's capabilities for such monitoring observations.
The FAST Telescope
The observations were made possible by FAST's high sensitivity combined with advanced data-processing techniques. Located in a natural karst depression, FAST is the world's largest single-dish radio telescope, with a reception area equivalent to 30 standard football fields. It began formal operations in January 2020 and was officially opened to global researchers in March 2021, serving as a facility for studies of pulsars, FRBs, and the interstellar medium.
Future Research
Ongoing long-term monitoring by FAST aims to determine the prevalence of binary systems among repeating FRB sources. An upgrade plan for FAST is underway, which involves deploying dozens of medium-aperture antennas around the main telescope to form a unique, FAST-centered giant synthetic aperture array. This upgrade is expected to enhance both sensitivity and resolution. Additionally, Shi Shengcai, an academician of CAS and a researcher at the PMO, noted plans for a 15-meter submillimeter telescope in Qinghai Province and a terahertz telescope at the South Pole, which will collaborate with FAST across different frequency bands to further explore cosmic mysteries.
Collaborating Institutions
The research involved a collaborative effort between institutions including The University of Hong Kong, Purple Mountain Observatory, Yunnan University, and the National Astronomical Observatories of the Chinese Academy of Sciences. The project received support from various national and international grants, with observing time provided by FAST and Australia's Parkes telescope.