Locating the Source of a Powerful Cosmic Explosion

MIT astronomers have developed a method to trace the origin of fast radio burst 20221022A, located 200 million light-years away. Published in Nature, the study marks a key step in understanding the origins of these mysterious cosmic phenomena.

Fast radio bursts (FRBs) are brief, intense explosions of radio waves emitted by compact objects such as neutron stars and possibly black holes. These fleeting bursts, lasting only a thousandth of a second, release immense energy, momentarily outshining entire galaxies.

Since the first FRB was discovered in 2007, thousands have been identified, with sources ranging from within our galaxy to as far as 8 billion light-years away. However, the exact mechanisms driving these cosmic radio flares remain uncertain.

Using a technique that analyzes the "scintillation" of radio signals—similar to the twinkling of stars—the researchers pinpointed the precise location of FRB 20221022A. By studying variations in the burst’s brightness, they determined that the signal originated close to its source, challenging some models that proposed more distant origins.

The team estimated that the burst came from within 10,000 kilometers of a rotating neutron star—a distance shorter than the span between Singapore and New York. This proximity suggests the burst originated in the neutron star's magnetosphere, the highly magnetic region surrounding the compact star.

The findings provide the first direct evidence that a neutron star's magnetosphere can serve as the source of a fast radio burst.

In these environments of neutron stars, the magnetic fields are really at the limits of what the universe can produce. There’s been a lot of debate about whether this bright radio emission could even escape from that extreme plasma.

Kenzie Nimmo, Study Lead Author and Postdoctoral Researcher, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology

“Around these highly magnetic neutron stars, also known as magnetars, atoms can’t exist—they would just get torn apart by the magnetic fields. The exciting thing here is, we find that the energy stored in those magnetic fields, close to the source, is twisting and reconfiguring such that it can be released as radio waves that we can see halfway across the universe,” added Kiyoshi Masui, associate professor of physics at MIT.

The co-authors of the study include Adam Lanman, Shion Andrew, Daniele Michilli, and Kaitlyn Shin from MIT, along with collaborators from multiple institutions.

Burst Size

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has significantly increased the detection of FRBs in recent years. The radio telescope array consists of four large, stationary, half-pipe-shaped receivers designed to capture radio emissions, making it highly sensitive to these rapid bursts.

Since 2020, CHIME has detected thousands of FRBs from across the universe. While the exact physics behind FRBs remains unclear, most experts agree they originate from extremely compact objects.

Some theories suggest FRBs arise from the turbulent magnetosphere surrounding a compact object, while others propose they originate farther out as part of a shockwave moving away from the source.

To differentiate between these scenarios, researchers analyzed the “scintillation” effect, where light from a bright source, like a star, passes through a medium such as gas in a galaxy. This bending of light creates a twinkling effect, with smaller or more distant objects twinkling more noticeably. In contrast, larger or closer objects, such as planets in our solar system, do not twinkle as much due to reduced bending.

By measuring the degree of an FRB’s scintillation, the researchers estimated the size of the region where the burst originated. A smaller region would suggest the burst came from the magnetically chaotic environment near the source, while a larger region would support the shockwave model.

Twinkle Pattern

The researchers tested this hypothesis using FRB 20221022A, detected by CHIME in 2022. The burst, lasting about two milliseconds, appeared typical in brightness but had a unique feature: its light was highly polarized, tracing a smooth S-shaped curve.

This polarization pattern, observed by collaborators at McGill University, is considered evidence that the FRB emission site is rotating, similar to patterns seen in pulsars—highly magnetized, rotating neutron stars. It was the first time such polarization had been observed in an FRB, suggesting the signal originated near a neutron star. A companion paper in Nature details these findings.

The MIT team used scintillation to further investigate FRB 20221022A. Examining CHIME data, they observed sharp brightness changes, indicating the burst was twinkling. This confirmed the radio signals were bent and filtered by gas located between the telescope and the FRB.

By identifying the location of this gas, the researchers confirmed some scintillation was caused by gas within the host galaxy of the FRB. Using this gas as a natural lens, they determined the burst originated from a small region about 10,000 kilometers across.

Nimmo explained, “This means that the FRB is probably within hundreds of thousands of kilometers from the source. That’s very close. For comparison, we would expect the signal would be more than tens of millions of kilometers away if it originated from a shockwave, and we would see no scintillation at all.”

“Zooming into a 10,000-kilometer region, from a distance of 200 million light years, is like being able to measure the width of a DNA helix, which is about 2 nanometers wide, on the surface of the moon. There’s an amazing range of scales involved,” stated Masui.

Together with McGill’s findings, the results rule out the theory that FRB 20221022A originated from the edge of a compact object. Instead, the study demonstrates for the first time that chaotic magnetic environments near neutron stars can produce FRBs.

“These bursts are always happening, and CHIME detects several a day. “There may be a lot of diversity in how and where they occur, and this scintillation technique will be really useful in helping to disentangle the various physics that drive these bursts,” said Masui.

Ryan Mckinven, a co-author from McGill University, added, “The pattern traced by the polarization angle was so strikingly similar to that seen from pulsars in our own Milky Way Galaxy that there was some initial concern that the source wasn't actually an FRB but a misclassified pulsar. Fortunately, these concerns were put to rest with the help of data collected from an optical telescope that confirmed the FRB originated in a galaxy millions of light-years away.”

“Polarimetry is one of the few tools we have to probe these distant sources. This result will likely inspire follow-up studies of similar behavior in other FRBs and prompt theoretical efforts to reconcile the differences in their polarized signals,” further added Mckinven.

Numerous organizations, including the University of British Columbia, the Canadian Institute for Advanced Research, the Trottier Space Institute at McGill University, the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto, and the Canada Foundation for Innovation, supported the study.

Journal Reference:

Nimmo, K, et al. (2025) Magnetospheric origin of a fast radio burst constrained using scintillation. Nature. doi.org/10.1038/s41586-024-08297-w