Astronomers analyzed the source of the second recorded repeating fast radio burst, FRB 190520. The powerful flares are accompanied by a steadier, weaker radio signal that persists between the bursts. This new finding prompts fresh questions about what drives these enigmatic events and whether the recurring radio output could serve as a tool for probing intergalactic space. The discovery and its implications were summarized in Nature.
FRB 190520 was first spotted on May 20, 2019 by the Five-hundred-meter Aperture Spherical Radio Telescope in China, known as FAST. In November that year, the instrument data revealed the repeating pattern. Subsequent investigations involved the Karl G. Jansky Very Large Array and other facilities to explore the object in more detail. FAST later confirmed that FRB 190520 emits highly repetitive radio pulses, a feature that sets it apart from the majority of nonrepeating fast radio bursts. In 2020, VLA observations helped pinpoint the source, which enabled optical follow-up with the Subaru Telescope in Hawaii. The optical data linked the bursts to the edge of a dwarf galaxy roughly three billion light-years away. The same cycles of strong flares were found to be interlaced with much weaker radio emission between bursts.
Coauthor Casey Low, affiliated with the California Institute of Technology, notes that the localization of FRB 190520 mirrors the pattern seen with the first burst of this kind identified in 2016, thanks in part to the VLA’s precise measurements. This early FRB, FRB 121102, marked a turning point by revealing details about the environment and distance of these events. With two similar objects now documented, scientists anticipate that these sources may belong to a distinct subclass, inviting a reevaluation of how fast radio bursts are categorized and understood.
A common method in this field involves estimating the density of the interstellar medium by examining how radio waves disperse during travel to Earth. Waves travel faster at higher frequencies, slower at lower ones, a pattern that helps gauge distance to pulsars. Yet for FRB 190520, the dispersion pattern points to distances much larger than usual; the scatter suggests a reach of roughly eight to nine and a half billion light-years. Researchers propose several explanations, including the possibility that the medium through which the waves pass is unusually dense. The team behind the study also suggests FRB 190520 may still be a relatively young source, potentially enveloped by a dense shell produced by a supernova. If so, the remnant would be a magnetar—a highly magnetized neutron star—that powers the observed radio activity.