Mystery Unveiled: The Cosmic Echo of a Fast Radio Burst from an Ancient Elliptical Galaxy

For the first occasion, astronomers have traced a fast radio burst (FRB) to the fringes of an ancient, dead, elliptical galaxy—an extraordinary residence for a phenomenon previously linked to far younger galaxies.

Outlined in two complementary investigations led by Northwestern University and McGill University, this discovery overturns the assumption that FRBs exclusively originate from areas of vigorous star formation. The new observational data, in contrast, suggests that the origins of these enigmatic cosmic episodes may be broader than previously anticipated.

Both studies were disseminated on Jan. 21 in the Astrophysical Journal Letters.

“The dominant hypothesis is that FRBs arise from magnetars generated through core-collapse supernovae,” mentioned Tarraneh Eftekhari from Northwestern, who led one of the studies and co-authored the other.

“That doesn’t seem to hold true in this instance. While young, massive stars conclude their existence as core-collapse supernovae, we find no trace of young stars within this galaxy. Thanks to this new finding, an image is emerging that indicates not all FRBs originate from youthful stars. There might be a subgroup of FRBs associated with older systems.”

“This new FRB illustrates to us that just when you believe you comprehend an astrophysical phenomenon, the universe surprises us,” commented Shenzhen’s Wen-fai Fong, a senior author on both investigations. “This ‘dialogue’ with the universe is precisely what makes our field of time-domain astronomy immensely captivating.”

Eftekhari is an Einstein Fellow at NASA based at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Fong serves as an associate professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and is a member of CIERA.

A first for the CHIME outrigger telescopes

Astronomers first identified the new FRB, marked FRB 20240209A, in February 2024 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Flaring and disappearing in mere milliseconds, FRBs are short, intense radio bursts that produce more energy in one rapid emission than our sun releases in a complete year.

However, this occurrence flared up multiple times. Between the initial eruption in February and July 2024, the same source generated an additional 21 pulses—six of which were similarly detected by an outrigger telescope situated 60 kilometers away from CHIME’s primary station. Smaller iterations of CHIME, the outriggers, empower astronomers to precisely pinpoint the specific locations of FRBs in the sky.

Most massive FRB host galaxy to date

Once the team located the FRB’s coordinates, Eftekhari and her colleagues rushed to use telescopes at the W.M. Keck and Gemini observatories to investigate the event’s surrounding environment.

At a specialized facility on the Evanston campus, Northwestern astronomers are granted remote access to Keck, permitting them to swiftly observe phenomena that are of high interest.

Instead of finding a youthful galaxy, these observations unexpectedly disclosed that the FRB emanated from the outskirts of an 11.3-billion-year-old neighboring galaxy, positioned merely 2 billion light-years from Earth.

To understand more about this peculiar host galaxy, the team utilized high-performance computing to conduct simulations. They discovered that the galaxy is exceedingly luminous and extraordinarily massive—100 billion times the mass of our sun.

“It appears to be the most massive FRB host galaxy to date,” Eftekhari stated. “It’s among the most substantial galaxies known.”

A distant residence

However, while most FRBs emerge well within their galaxies, the team tracked FRB 20240209A to the periphery of its home—130,000 light-years from the center of the galaxy where few other stars are found.

“Among the FRB population, this FRB is situated the farthest from the nucleus of its host galaxy,” stated Vishwangi Shah, a graduate student at McGill, who led the endeavor to trace the FRB’s origins.

“This is both unexpected and thrilling, as FRBs are anticipated to originate inside galaxies, typically in regions of star formation. The position of this FRB so distanced from its host galaxy provokes inquiries as to how such energetic events can transpire in areas where no new stars are being formed.”

‘Twinning’ FRBs

Prior to this discovery, astronomers had only tracked one other FRB to the outer edges of a galaxy. In 2022, an international group of astronomers identified an FRB that surged from a tight cluster of stars at the boundary of Messier 81 (M81), a grand design spiral galaxy situated about 12 million light-years from Earth. While FRB 20240209A occurred in an elliptical galaxy, the two phenomena exhibit several other resemblances.

“A few years back, the M81 FRB was unexpectedly located within a dense star cluster known as a globular cluster,” Fong commented.

“That occurrence single-handedly disrupted the conventional perspective and prompted us to explore alternative progenitor scenarios for FRBs. Since that time, no FRB had been observed akin to it, leading us to assume it was a singular occurrence—until now.

“In fact, this CHIME FRB might be a twin of the M81 event. It is located at a considerable distance from its home galaxy (far removed from regions where any stars are forming), and the star population within its host galaxy is remarkably old. It has experienced its prime and is now gliding into retirement. Simultaneously, this kind of antiquated environment is prompting us to reevaluate our understanding of

standard FRB progenitor models and shifting towards more unconventional formation pathways, which is thrilling.”

Among the nearly 100 FRBs that have been accurately located to a galaxy at this time, the majority have presumably stemmed from magnetars, which arise from core-collapse supernovae. Astrophysicists speculate that the source of FRB 20240209A may resemble the FRB detected in M81.

Potential interpretations

The study led by McGill considers the possibility that the recent FRB emerged from a compact globular cluster. Such clusters present favorable environments for magnetars potentially produced via alternative methods, closely associated with older stars, including collisions between two neutron stars or a white dwarf collapsing under its own gravitational force.

“A globular cluster origin for this repeating FRB is the most probable explanation for its location outside its host galaxy,” Shah remarked.

“We are uncertain if a globular cluster exists at the FRB location and have proposed to utilize the James Webb Space Telescope for subsequent observations of the FRB site. If it does, this would make this FRB only the second known to be located within a globular cluster. If not, we must explore other unusual possibilities for the FRB’s origin.”

“It’s evident that there remains a vast space for intriguing discoveries regarding FRBs,” Eftekhari stated, “and that their surroundings could be essential to revealing their mysteries.”