An international collaboration of astronomers, including from the University of Toronto, have detected the brightest Fast Radio Burst (FRB) to date - and have been able to pinpoint its location in a nearby galaxy by using a network of radio telescopes.
FRBs are extremely energetic flashes from distant sources from across the universe that are caused by extreme astrophysical phenomena. Yet, they remain poorly understood by scientists and are among astronomy's most mysterious phenomena. Pinpointing their location promises to usher in a new era of discovery, allowing scientists to trace their true cosmic origins.
The new FRB signal, called FRB 20250316A and playfully nicknamed RBFLOAT ("Radio Brightest Flash Of All Time"), was very precisely localized using a new FRB Outrigger array as part of the Canadian Hydrogen-Intensity Mapping Experiment (CHIME), which has detected thousands of FRBs since 2018. These smaller versions of the CHIME instrument - located in British Columbia, Northern California and West Virginia - allow astronomers to perform Very Long Baseline Interferometry (VLBI), a technique that can pinpoint the location of FRBs with unprecedented accuracy.
"We were ultimately extremely lucky that we were able to pinpoint the precise sky position of this rare event," said Mattias Lazda, a U of T PhD student in the David A. Dunlap department of astronomy and astrophysics in the Faculty of Arts & Science, who is an author on two new papers about the discovery.
"A few hours after we detected it, we experienced a power outage at one of our telescope sites that played a critical role in telling us where the burst came from. Had the event happened any later that day, we would've completely missed our chance."
Although FRBs are among the most powerful radio sources in the universe, they last only a few milliseconds to seconds, briefly outshining all other radio sources in their galaxy. RBFLOAT, detected on March 16, 2025, lasted only about one fifth of a second.
"Cosmically speaking, this fast radio burst is just in our neighbourhood," says Kiyoshi Masui, associate professor of physics and affiliate of MIT's Kavli Institute for Astrophysics and Space Research, who is a U of T alum. "This means we get this chance to study a pretty normal FRB in exquisite detail."
RBFLOAT was so bright because the source was relatively nearby in the outskirts of a galaxy called NGC 4141, which is about 130 million light-years away in the constellation Ursa Major. The signal was traced to a region 45 light-years across - smaller than the average star cluster - representing an unprecedented spatial resolution.
It is equivalent to observing a guitar pick from 1,000 kilometres away.
"The discovery was very exciting, because we had our brightest ever event right after all three outriggers were online," said Amanda Cook, a Banting postdoctoral researcher at McGill University and a U of T alum who led the paper describing RBFLOAT. "Immediately, even though it was a Sunday afternoon, a bunch of us piled into a Zoom room and started hacking away at the research, hoping to get follow-up observations on source as quickly as possible."
The level of detail provided by the CHIME/FRB Outrigger array allowed the team to follow up with observations from the James Webb Space Telescope (JWST) and capture a faint infrared signal that matched the location of RBFLOAT. This surprised the researchers who are left wondering if the spot is a red giant star or a fading light echo from the burst itself.
"The high resolution of JWST allows us to resolve individual stars around an FRB for the first time. This opens the door to identifying the kinds of stellar environments that could give rise to such powerful bursts, especially when rare FRBs are captured with this level of detail." said Peter Blanchard, a Harvard postdoctoral fellow and lead author of the companion paper describing the JWST observation.
Despite being the brightest ever seen by CHIME, astronomers have not detected repeat bursts from the source, even when looking back over the hundreds of hours of CHIME observations of its position over more than six years.
"This burst doesn't seem to repeat, which makes it different from most well-studied FRBs," said Cook. "That challenges a major idea in the field, that all FRBs repeat, and opens the door to reconsidering more 'explosive' origins for at least some of them."
Two studies describing the phenomenon were published in the Astrophysical Journal Letters: one is focused on the original radio discovery and localization of the burst ; the other details the JWSTs near-infrared images of the location from which the radio burst originated . Together, they offer new detail and new possibilities for studying FRBs - not just as cosmic curiosities, but as tools to probe the universe.
