The fast radio burst (FRB) enigma that has baffled astronomers for years is more diverse than previously anticipated, according to Northwestern and McGill scientists who have uncovered the rapid emissions coming from an unexpectedly point of origin: an ancient dead galaxy.
Since astronomers discovered the first FRB in 2007, a consensus has been forming around the hypothesis that the bursts originate from magnetars formed through the core collapse of a supernova in a young galaxy.
Now researchers are reconsidering those assumptions, as the newly discovered FRB defies standard behavior, according to findings detailed in two new studies.
New FRB, Old Space
“This new FRB shows us that just when you think you understand an astrophysical phenomenon, the universe turns around and surprises us,” said lead author on one paper, Wen-fai Fong. “This ‘dialogue’ with the universe is what makes our field of time-domain astronomy so incredibly thrilling.”
In February 2024, astronomers first detected FRB 20240209AA using the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Within milliseconds, the burst released more energy than Earth’s sun in a year. Between February and July, 22 such events occurred, with six confirmed by an outrigger telescope a few miles from CHIME. CHIME hosts several earth-bound satellite locations called outriggers to more accurately locate where in the sky FRBs originate.
Deepening The Search
Armed with these coordinates, the Northwestern team expanded their research to include other advanced sensing platforms for zeroing in on FRB sources.
“Northwestern has specialized institutional access to the W. M. Keck Observatories which enables us access to the telescopes. As Keck is among the most sensitive observatories globally, and has an extremely versatile instrument suite, this access was crucial for taking sensitive astronomical observations of the galaxy in unprecedented detail,” Fong told The Debrief.
Additionally, Tarraneh Eftekhari, lead author on one study and co-author on another, is Principal Investigator on the Gemini Observatory’s Large and Long Program. “This gives her access to hundreds of hours over a few years dedicated to the study of fast radio bursts. This program just got started, so with this new discovery, we started it with a bang!” Fong said.
Analyzing An Ancient And Massive Fast Radio Burst Source
After collating data the team collected, their analysis yielded a few shocking results. The astronomers were amazed to find an 11.3 billion-year-old elliptical galaxy within 2 billion light years of Earth, rather than the younger variety normally associated with FRBs. The team then ran computer simulations to discover that the galaxy is 100 billion times the mass of our sun, and extremely luminous.
“We were definitely surprised to find that this galaxy was incredibly old—much older than any other FRB host galaxy we’ve seen so far,” Eftekhari said. “When we tested our simulations under different assumptions, our findings remained consistent.”
“It seems to be the most massive FRB host galaxy to date,” Eftekhari added. “It’s among some of the most massive galaxies out there.”
Further Strange Fast Radio Burst Behavior
Additionally, the FRB played against norms by originating 130,000 lightyears from its galactic center in a desolate region of space. Normally, FRBs are expected to originate from a more centralized location.
“Among the FRB population, this FRB is located the furthest from the center of its host galaxy,” said Vishwangi Shah, a graduate student at McGill, who led the effort to pinpoint the FRB’s origins. “This is both surprising and exciting, as FRBs are expected to originate inside galaxies, often in star-forming regions. The location of this FRB so far outside its host galaxy raises questions as to how such energetic events can occur in regions where no new stars are forming.”
A Cosmic Kindred Spirit
In 2022, an international team uncovered the only other FRB emanating from the edges of its host galaxy. That burst came from the fringes of the M81 spiral galaxy, about 12 million lightyears from Earth. Despite coming from different types of galaxies, spiral and elliptical, the events were remarkably similar.
“A few years ago, the M81 FRB was surprisingly discovered within a dense cluster of stars called a globular cluster,” Fong said. “That event single-handedly halted the conventional train of thought and made us explore other progenitor scenarios for FRBs. Since then, no FRB had been seen like it, leading us to believe it was a one-off discovery — until now.”
“In fact, this CHIME FRB could be a twin of the M81 event. It is far from its home galaxy (far away from where any stars are being born), and the population of stars in its home galaxy is extremely old. It’s had its hey-day and is now coasting into retirement,” Fong continued. “At the same time, this type of old environment is making us rethink our standard FRB progenitor models and turning to more exotic formation channels, which is exciting.”
These recent FRBs contradict the vast majority of the rest of the almost 100 known FRBS believed to originate from magnetars at the center of young galaxies.
Explaining An Abnormal Fast Radio Burst
One of the new studies concluded that a dense globular cluster, a likely site for magnetars, formed from older stars through unusual methods.
“A globular cluster origin for this repeating FRB is the most likely scenario to explain why this FRB is located outside its host galaxy,” Shah said. “If yes, it would make this FRB only the second FRB known to reside in a globular cluster. If not, we would have to consider alternative exotic scenarios for the FRB’s origin.”
“It’s clear that there’s still a lot of exciting discovery space when it comes to FRBs,” Eftekhari added, “and that their environments could hold the key to unlocking their secrets.”
Continuing The Search
As Fong noted, the Gemini program is off to an exciting start, but it’s only the beginning.
“Thanks to our Gemini Large and Long Program and the CHIME outriggers, which will pinpoint hundreds of FRBs to exact sky positions, we are uniquely positioned to explore the diversity in environments from which these mysterious signals emerge.” Eftekhari said, emphasizing how she and her colleagues will leverage that initiative in the future.
Even with all of these resources at their disposal, the Northwestern and McGill astronomers are seeking to expand their reach even further with highly coveted time on the James Webb Space Telescope.
“For this particular event, we’ve submitted a proposal for the James Webb Telescope in the hopes of studying the immediate environment around the FRB to learn more about its precise origins,” Eftekhari said.
“More broadly, as we collect more data and pinpoint more FRBs to their host galaxies, I’m curious to see whether any patterns start to appear,” Eftekhari concluded, noting many questions that remain.
“Will we find that repeating FRBs more commonly occur in a specific type of galaxy? Are there any correlations between the FRB signals themselves and the types of galaxies in which they emerge?”
The paper “The Massive and Quiescent Elliptical Host Galaxy of the Repeating Fast Radio Burst FRB 20240209A” appeared on January 21, 2025 in The Astrophysical Journal Letters.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.