The source of the newly-detected fast radio burst, FRB 20240209A, is in the distant outskirts of an ancient elliptical galaxy, which is located 2 billion light-years from Earth and has a mass of more than 100 billion solar masses. Young stellar remnants that theorists think produce such bursts of radio waves should have disappeared long ago in this 11.3-billion-year-old galaxy. Detailed in two complementary studies in the Astrophysical Journal Letters, the discovery shatters assumptions that fast radio bursts solely emanate from regions of active star formation.
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Gemini image showing the host galaxy of FRB 20240209A (cyan crosshairs) and the localization ellipses. Image credit: Shah et al., doi: 10.3847/2041-8213/ad9ddc.
“The prevailing theory is that fast radio bursts (FRBs) come from magnetars formed through core-collapse supernovae,” said Northwestern University astronomer Tarraneh Eftekhari.
“That doesn’t appear to be the case here. While young, massive stars end their lives as core-collapse supernovae, we don’t see any evidence of young stars in this galaxy.”
“Thanks to this new discovery, a picture is emerging that shows not all FRBs come from young stars.”
“Maybe there is a subpopulation of FRBs that are associated with older systems.”
“This new FRB shows us that just when you think you understand an astrophysical phenomenon, the universe turns around and surprises us,” added Northwestern University astronomer Wen-fai Fong.
“This ‘dialogue’ with the Universe is what makes our field of time-domain astronomy so incredibly thrilling.”
FRB 20240209A was discovered in February 2024 by the Canadian Hydrogen Intensity Mapping Experiment (CHIME).
Flaring up and disappearing within milliseconds, FRBs are brief, powerful radio blasts that generate more energy in one quick burst than our sun emits in an entire year.
But FRB 20240209A flared up more than once — between the initial burst in February through July 2024, the same source produced another 21 pulses.
After the team pinpointed the FRB’s position, the astronomers hurried to use telescopes at the W.M. Keck and Gemini observatories to explore the event’s surrounding environment.
Instead of finding a young galaxy, these observations surprisingly revealed that the FRB originated at the edge of an 11.3-billion-year-old neighboring galaxy, located 2 billion light-years from Earth.
To learn more about this unusual host galaxy, the researchers used high-performance computers to run simulations.
They found that the galaxy is extremely luminous and incredibly massive — 100 billion times the mass of our Sun.
“It seems to be the most massive FRB host galaxy to date. It’s among some of the most massive galaxies out there,” Dr. Eftekhari said.
While most FRBs originate well within their galaxies, the authors traced FRB 20240209A to the outskirts of its home — 130,000 light-years from the galaxy’s center where few other stars exist.
“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 University.
“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.”
According to the team, FRB 20240209A likely originated within a dense globular cluster.
Such clusters are promising sites for magnetars possibly formed through other mechanisms and associated with older stars, including through the merger of two neutron stars or from a white dwarf collapsing under its own gravity.
“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.
“We do not know for a fact if there is a globular cluster present at the FRB position and have submitted a proposal to use the NASA/ESA/CSA James Webb Space Telescope for follow-up observations of the FRB location.”
“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, and that their environments could hold the key to unlocking their secrets,” Dr. Eftekhari said.
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T. Eftekhari et al. 2025. The Massive and Quiescent Elliptical Host Galaxy of the Repeating Fast Radio Burst FRB 20240209A. ApJL, in press; arXiv: 2410.23336
Vishwangi Shah et al. 2025. A Repeating Fast Radio Burst Source in the Outskirts of a Quiescent Galaxy. ApJL 979, L21; doi: 10.3847/2041-8213/ad9ddc
