Vancouver, B.C. — In a discovery that reframes how astronomers think about fast radio bursts, researchers with Canada's CHIME telescope have detected a repeating fast radio burst (FRB) that pulses with remarkable regularity on a cycle of approximately 16 days.
The breakthrough, reported by the CHIME/FRB Collaboration, concerns FRB 180916.J0158+65, a distant source that repeats its bursts in a pattern: roughly five days of activity followed by twelve days of silence. It is the first fast radio burst ever documented to exhibit such precise periodicity.
"This is the kind of discovery that changes what we think we're looking at," said Pragya Shrestha, an astrophysicist involved in the analysis. The finding suggests that models invoking magnetars—neutron stars with extraordinarily strong magnetic fields—as the underlying power source may need refinement. A truly random magnetar is unlikely to produce such clockwork repetition.
What CHIME Sees
The Canadian Hydrogen Intensity Mapping Experiment operates across the entire northern sky in real time, its antenna array sweeping thousands of sources each second. When a fast radio burst arrives—a microsecond-to-millisecond flash of radiation across multiple radio frequencies—CHIME captures it and measures what's called the dispersion measure: how much the signal's lower frequencies lag behind its higher frequencies as they travel through the intergalactic medium.
Dispersion measure is the astronomer's distance ruler. As radio waves travel through space, they encounter free electrons in the ionized gas between galaxies. Lower frequencies move more slowly through this "soup" of particles, creating a time delay proportional to distance. By measuring the dispersion, astronomers can confirm that FRB 180916.J0158+65 originates well beyond our Milky Way—a prerequisite for it to qualify as a bona fide FRB.
The source is located approximately 500 million light-years away, in a small galaxy that appears to be forming stars at a moderate rate. The burst itself arrives as a radio pulse carrying as much energy in a fraction of a second as the Sun emits in hours.
The Periodicity Problem
Before CHIME's detection, astronomers had catalogued dozens of FRBs, but nearly all appeared to be one-off events. A handful of repeating sources had been found—most notably FRB 121102, which bursts repeatedly and has allowed follow-up observations with radio interferometers—but none had shown such regular timing.
The 16-day cycle opens new questions. What astrophysical mechanism produces such regularity? The leading hypothesis remains a magnetar—a neutron star whose magnetic field is so intense (10^15 Gauss or stronger) that it can crack the star's crust, releasing enormous energy. But a naked magnetar has no obvious reason to pulse with a 16-day period. The periodicity suggests an orbital companion or a rotating structure within the magnetar's magnetosphere.
"This could be a neutron star and a white dwarf in a tight orbit, where the magnetar's emission beam sweeps across us periodically," offered another member of the team. "Or it could be precession—the magnetar's spin axis wobbling like a top, causing the beam to point toward us and away in a regular rhythm."
Other models invoke a binary system: perhaps a magnetar orbiting another compact object, with tidal forces modulating the burst rate. Yet others propose that the periodicity emerges from internal oscillations within the magnetar itself—a kind of cosmic metronome driven by the star's internal magnetic turbulence.
What Comes Next
The CHIME/FRB Collaboration has continued monitoring FRB 180916.J0158+65, collecting hundreds of bursts to refine the period measurement and search for deviations that might reveal the underlying mechanism. Other major facilities—including the Very Large Array in New Mexico and the European VLBI Network—have joined the effort, cross-checking CHIME's detections and gathering additional data on the burst's polarization (the orientation of its electromagnetic waves) and spectral properties.
Dispersion measure variations across the bursts' frequencies also carry information about the source's local environment. A dense magnetosphere or circumstellar material would leave its signature in how the dispersion changes from burst to burst. Early analysis suggests the source's environment is relatively clean, though detailed models are still being refined.
The periodicity of FRB 180916.J0158+65 has already influenced SETI thinking. While fast radio bursts are of natural origin, the regularity shows that cosmic radio signals can carry temporal structure. A sufficiently regular artificial beacon—encoded with periodicity—might be distinguishable from natural astrophysical noise. It's a reminder that the universe's natural radio repertoire is far richer and stranger than we once imagined.
"Every time we think we understand what these objects are," Shrestha noted, "they surprise us again. That's what makes them so compelling to study."