Fast radio bursts (FRBs) are enigmatic and fleeting signals of radio waves that were initially believed to originate from magnetars, which are neutron stars with strong magnetic fields. However, these magnetars are usually found in young star clusters. Recently, a repeating burst identified last year was traced to the distant edges of an old, massive elliptical galaxy. This raises doubts about whether magnetars could actually be the source of FRBs.
Calvin Leung, an astronomer, was thrilled last summer when he analyzed data from a newly activated radio telescope, successfully locating the source of repeated intense radio waves—known as fast radio bursts (FRBs)—coming from the northern constellation Ursa Minor.
Leung, who holds a Miller Postdoctoral Fellowship at the University of California, Berkeley, aims to uncover the origins of these enigmatic bursts and utilize them as tools to explore the vast structure of the universe, which is crucial to understanding its beginnings and development. He crafted much of the computer code that allowed his team to merge data from numerous telescopes, enabling them to pinpoint the location of a burst with remarkable precision.
However, the excitement quickly turned into confusion when his fellow researchers from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) utilized optical telescopes to observe the site and found that it was located in the outlying areas of a long-vanished elliptical galaxy, which theoretically shouldn’t house stars responsible for such bursts.
Instead of the anticipated “magnetar”—a highly magnetized and spinning neutron star resulting from the collapse of a massive young star—”the new question became: How can there be a magnetar found in this ancient, lifeless galaxy?” Leung stated.
The young stellar remnants expected to produce these rapid bursts of radio signals should have disappeared long ago from this 11.3-billion-year-old galaxy, situated 2 billion light years away from Earth and possessing over 100 billion times the mass of the sun.
Vishwangi Shah, a doctoral student from McGill University in Montreal, Canada, who refined and further developed Leung’s calculations about the burst location, noted, “This is not just the first FRB located outside a dead galaxy, but it is also the farthest away from its home galaxy compared to all other FRBs. The burst’s positioning is unexpected and poses questions about how such powerful bursts can occur in areas where new star formation has halted.”
Shah is the lead author of a study detailing the FRB published today (Tuesday, Jan. 21) in the Astrophysical Journal Letters, alongside another paper from colleagues at Northwestern University in Evanston, Illinois. Leung, a co-author on both studies, is also a key developer of three additional telescopes—known as outriggers—connected to the main CHIME radio array situated near Penticton, British Columbia. He mentored Shah at McGill while pursuing his doctoral studies at the Massachusetts Institute of Technology (MIT) and later completed an Einstein Postdoctoral Fellowship at UC Berkeley before his Miller fellowship.
New CHIME Outrigger in California
A third outrigger radio array will be operational this week at Hat Creek Observatory, which, formerly run by UC Berkeley, is now under the management of the SETI Institute located in Mountain View. Together, these four arrays greatly enhance CHIME’s ability to accurately locate FRBs.
“With the three outriggers, we should be able to accurately identify one FRB per day to its respective galaxy, which is significant,” Leung remarked. “That represents a 20-fold improvement over CHIME operating with only two outrigger arrays.”
This enhanced precision will allow optical telescopes to target and identify the types of star groups, such as globular clusters or spiral galaxies, responsible for these bursts, potentially pinpointing the stellar source. Out of the approximately 5,000 sources detected so far—over 95% of which were found by CHIME—few have been traced to a specific galaxy, complicating efforts to verify whether magnetars or other types of stars generate these emissions.
In the new study, Shah averaged multiple bursts from the repeating FRB to increase the accuracy of the pinpointing achieved by the CHIME array and one outrigger array in British Columbia. Following its revelation in February 2024, astronomers noted 21 additional bursts through July 31. Since the submission of the study, Shion Andrew at MIT integrated data from another outrigger at the Green Bank Observatory in West Virginia, confirming Shah’s findings with an accuracy improved by 20 times.
“This finding challenges current theories linking the origins of FRBs to events in star-forming galaxies,” Shah indicated. “The source may be situated within a globular cluster, a dense assembly of ancient, dead stars outside the main galaxy. If substantiated, this would make FRB 20240209A only the second FRB associated with a globular cluster.”
However, she pointed out that the other FRB linked to a globular cluster was tied to a live galaxy, unlike this old elliptical galaxy where star formation ceased billions of years ago.
“It’s apparent that there’s still a wealth of discovery potential regarding FRBs, and their environments might be key to unlocking their mysteries,” stated Tarraneh Eftekhari, who holds an Einstein Postdoctoral Fellowship at Northwestern and is the lead author of the second paper.
“CHIME and its outrigger telescopes will enable us to conduct astrometry at an unprecedented level compared to the Hubble Space Telescope or the James Webb Space Telescope. It will be up to those telescopes to delve deeper to identify the source,” Leung added. “It’s an incredible radio telescope.”
The research was funded by several institutions, including the Gordon and Betty Moore Foundation, NASA, the Space Telescope Science Institute, the National Science Foundation, the David and Lucile Packard Foundation, the Alfred P. Sloan Foundation, the Research Corporation for Science Advancement, the Canadian Institute for Advanced Research, the Natural Sciences and Engineering Council of Canada, the Canada Foundation for Innovation, and the Trottier Space Institute at McGill.
