Astronomers have found compelling evidence that at least some fast radio bursts originate from stars in binary systems rather than from isolated objects.
An international group of astronomers, including a researcher from the Department of Physics at The University of Hong Kong (HKU), has identified the strongest evidence so far that some fast radio bursts (FRBs) come from stars in binary systems. FRBs are extremely brief yet intense bursts of radio waves from distant galaxies. The new results show that, in these cases, the source is not a lone star as long believed, but part of a system where two stars orbit one another.
The team made the discovery using the Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou, widely known as the “China Sky Eye.” Their observations revealed a distinctive signal that points to the presence of a nearby companion star interacting with the FRB source. Reported in the journal Science, the findings are based on almost 20 months of continuous monitoring of a repeating FRB located roughly 2.5 billion light-years from Earth.
A rare signal: the RM flare
The properties of polarized radio waves offer valuable clues about the environment surrounding an FRB source. In this study, researchers detected an unusual event called an ‘RM flare’—a sudden and extreme shift in the polarization of the radio signal. This effect is thought to occur when material from a coronal mass ejection (CME) released by a companion star briefly passes through the region around the FRB source.
“This finding provides a definitive clue to the origin of at least some repeating FRBs,” said Professor Bing ZHANG, Chair Professor of Astrophysics of the Department of Physics and Founding Director of the Hong Kong Institute for Astronomy and Astrophysics at HKU, and a corresponding author of the paper. “The evidence strongly supports a binary system containing a magnetar—a neutron star with an extremely strong magnetic field, and a star like our Sun.”
Monitoring repeating FRBs with FAST
Fast radio bursts last only milliseconds but can outshine entire galaxies in radio energy. Most are seen just once, but a small number repeat, allowing astronomers to track them over long periods and search for subtle changes. Since 2020, FAST has played a central role in monitoring these repeating FRBs as part of a dedicated FRB Key Science Program co-led by Professor Bing Zhang.
One of these targets, known as FRB 220529A, was among the repeating sources observed regularly with FAST, ultimately leading to the breakthrough detection.
“FRB 220529A was monitored for months and initially appeared unremarkable,” said Professor Bing Zhang. “Then, after a long-term observation for 17 months, something truly exciting happened.”
Tracing the signal through space
FRBs are known for their near 100% linear polarization. As radio waves travel through a magnetized plasma, their polarization angle rotates with frequency—an effect known as Faraday rotation, measured by the rotation measure (RM).
“Near the end of 2023, we detected an abrupt RM increase by more than a factor of a hundred,’ said Dr. Ye LI of Purple Mountain Observatory and the University of Science and Technology of China, the paper’s first author.
“The RM then rapidly declined over two weeks, returning to its previous level. We call this an ‘RM flare’.”
Such a short-lived RM change is consistent with a dense magnetized plasma briefly crossing the line of sight.
“One natural explanation is that a nearby companion star ejected this plasma,” explained Professor Bing Zhang.
“Such a model works well to interpret the observations,” said Professor Yuanpei YANG, a professor from Yunnan University and a co-first author of the paper. “The required plasma clump is consistent with CMEs launched by the Sun and other stars in the Milky Way.”
Although the companion star cannot be directly observed at this distance, its presence was revealed through continuous radio observations with FAST and Australia’s Parkes telescope.
“This discovery was made possible by the persevering observations using the world’s best telescopes and the tireless work of our dedicated research team,” said Professor Xuefeng WU of Purple Mountain Observatory and the University of Science and Technology of China, the lead corresponding author.
The discovery also supports a recent unified physical picture proposed by Professor Bing Zhang and his collaborator, in which all FRBs originate from magnetars, with interactions in binary systems enabling a preferred geometry that allows more frequent, repeating bursts. Continued long-term monitoring of repeating FRBs may reveal how common binary systems are among these mysterious sources.
Reference: “A sudden change and recovery in the magnetic environment around a repeating fast radio burst” by Y. Li, S. B. Zhang, Y. P. Yang, C. W. Tsai, X. Yang, C. J. Law, R. Anna-Thomas, X. L. Chen, K. J. Lee, Z. F. Tang, D. Xiao, H. Xu, X. L. Yang, G. Chen, Y. Feng, D. Z. Li, R. Mckinven, J. R. Niu, K. Shin, B. J. Wang, C. F. Zhang, Y. K. Zhang, D. J. Zhou, Y. H. Zhu, Z. G. Dai, C. M. Chang, J. J. Geng, J. L. Han, L. Hu, D. Li, R. Luo, C. H. Niu, D. D. Shi, T. R. Sun, X. F. Wu, W. W. Zhu, P. Jiang and B. Zhang, 15 January 2026, Science.
DOI: 10.1126/science.adq3225
The project received support from the National Natural Science Foundation of China and other national and international grants from the collaborators. Observing time was provided by the FAST FRB Key Science Project (W.-W. Zhu and B. Zhang as Co-PIs), a FAST DDT program (coordinated by X.-F. Wu and P. Jiang), as well as FAST and Parkes PI projects (PIs: Y. Li and S. B. Zhang).
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