An international team has discovered a new type of radio emission originating from a red dwarf star. Astronomers from Peking University in China and ASTRON, the Netherlands Institute for Radio Astronomy, found the radio emission sweeps in frequency more rapidly than expected. They used the sweep as a tool to zoom-into the star and detect magnetic structures on its surface that were too small to be detected with conventional methods. The findings were published in the scientific journal Science Advances.
Published by the editorial team, 17 October 2025
Strong fields around starspots
Red dwarfs are stars smaller and cooler than the Sun—and the most common type of star in our Galaxy. They often possess much stronger magnetic fields than the Sun, which are thought to create harsh space weather conditions for any orbiting exoplanets. However, our understanding of stellar magnetic fields has so far been limited to large-scale structures, as there has been no effective way to directly probe small, localized regions such as starspots. These small-scale fields are especially important because they can trigger stellar eruptive events that affect the habitability of nearby planets.
Fine radio features
The team observed the red dwarf AD Leo using China’s Five-hundred-meter Aperture Spherical Telescope (FAST). Thanks to the telescope’s exceptional sensitivity, they identified fine details in the radio emission lasting only a few tens of milliseconds. Remarkably, these millisecond-scale bursts changed frequency—like a rapidly sliding musical note—at an extraordinary rate of about 8 gigahertz per second.
“The sweep rate we found from these bursts were incredibly fast, suggesting that the emission was coming from a small magnetic arch on the star,” said Jiale Zhang, the study’s lead author.
The team believes the frequency sweeps are produced when electrons bounce back and forth between the two ends of a magnetic arch anchored on starspots—regions of intense magnetic activity that can drive powerful stellar flares. While similar arches are routinely imaged on the Sun, the vast distances to other stars make them impossible to observe directly.
“We previously had hints of vigorous energy release in these magnetic arches from X-ray observations of red dwarfs,” Jiale Zhang explained. “But this new radio-based method gives us a direct way to estimate the size of the arches and better understand how they work. The arches are where all the space-weather events originate, and our approach adds a powerful new tool for studying them.”
Looking ahead
The team now plans to apply this technique to other types of stars to determine whether such fast frequency sweeps are common. These observations will help reveal how stellar magnetic arches erupt and shape the space-weather environments around their exoplanets. The paper’s first author is Jiale Zhang, a visiting student at ASTRON.
Paper: Starspots as the origin of ultrafast drifting radio bursts from an active M dwarf