For the first time, astronomers have discovered clear evidence that some fast radio bursts (FRBs) are emitted by binary stars, according to an international team of researchers.
The powerful yet brief bursts of radio waves emanate from distant galaxies and have puzzled scientists for some time, until a general consensus emerged that they are produced by isolated, single stars.
Now, a recent paper published in Science challenges that idea, based on observations of FRB 220529A made possible by the Five-hundred-meter Aperture Spherical Telescope (FAST), also known as China’s Sky Eye, which demonstrates that binary systems can produce FRBs.
The China Sky Eye
Located in southwestern China’s Guizhou province, FAST is also nicknamed “Tianyan,” which translates to “Heaven’s Eye” or “Sky Eye.” The radio telescope features a 1,640-foot-diameter dish, making it the largest single-dish telescope in the world, nestled within a natural depression.
The bright, millisecond-long flashes known as FRBs travel to us from distant galaxies. Generally, they are singular events, but the rare repeaters offer scientists intriguing opportunities to study the phenomena over longer periods and observe changes. Since 2020, Professor Bing Zhang has co-led a program to study these repeating FRBs. They found something remarkable in FRB 220529A, located 2.5 billion light-years from Earth.
“FRB 220529A was monitored for months and initially appeared unremarkable,’ said co-author Professor Bing Zhang. ‘Then, after a long-term observation for 17 months, something truly exciting happened.” The researchers used FAST to monitor the FRB for 20 months, eventually revealing that the source had a companion star.
Fast Radio Burst Polarization
Analyzing a radio wave’s polarization properties offers important clues about its source’s surroundings. In this FRB, the most notable feature was a sudden and dramatic polarization change known as an RM flare, indicative of a coronal mass ejection from a companion star interfering with the burst source.
“This finding provides a definitive clue to the origin of at least some repeating FRBs,” said co-author 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. “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.”
An FRB’s linear polarization allows researchers to track its journey through space. Due to the Faraday rotation effect, a radio wave’s polarization angle rotates when it travels through magnetized plasma. That rotation can be precisely measured using a quantity called a rotation measure (RM).
“Near the end of 2023, we detected an abrupt RM increase by more than a factor of a hundred,” said lead author Dr Ye LI of Purple Mountain Observatory and the University of Science and Technology of China. “The RM then rapidly declined over two weeks, returning to its previous level. We call this an ‘RM flare’.”
Binary Sourced Fast Radio Bursts
A brief RM change like this is consistent with the FRB having intercepted a dense magnetized plasma, likely ejected from a companion star.
“Such a model works well to interpret the observations,” said co-first author Professor Yuanpei Yang, a professor from Yunnan University. “The required plasma clump is consistent with CMEs launched by the Sun and other stars in the Milky Way.”
Directly observing the companion star over these billions of light-years was not feasible, but FAST and supplemental observations from the Parkes telescope in Australia successfully confirmed its presence.
“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 co-lead author Professor Xuefeng Wu of Purple Mountain Observatory and the University of Science and Technology of China.
The work supports a proposal by Professor Bing Zhang that FRBs are generated by magnetars and that binary systems produce a geometry that allows bursts to occur more frequently, and marks the beginning of ongoing studies required to determine how common binary systems are as sources of FRBs.
The paper, “A Sudden Change and Recovery in the Magnetic Environment Around a Repeating Fast Radio Burst,” appeared in Science on January 15, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.