Fast radio bursts are sudden flashes of radio waves, often lasting mere milliseconds. The first appeared on astronomers’ radar in 2007, and for the most part, still remain a complete mystery.
Scientists have since recorded thousands of them across the sky, each leaving behind questions about what kind of cosmic drama can generate such concentrated energy in so little time.
The bursts usually come from far beyond our own galaxy, making them challenging to trace back to a specific source.
Last summer, one set of repeated bursts caught special attention. Intense radio signals in the northern constellation Ursa Minor suggested something unusual. Initial data pointed to a source lying well outside our galactic neighborhood.
Researchers worked to narrow down its origin with a newly commissioned radio telescope that could combine signals from multiple arrays.
They hoped to piece together a more precise map of these flashes to get clues about how and where they formed.
Unexpected FRB source
Astronomer Calvin Leung, a Miller Postdoctoral Fellowship recipient at the University of California, Berkeley, helped develop the computer code that made it possible to pinpoint the fast radio bursts with high accuracy.
When he and his team plotted the signals, they found that the source sat in the distant outskirts of an ancient elliptical galaxy about 2 billion light years from Earth.
This galaxy is around 11.3 billion years old, leading experts to believe it should not contain the kind of young, magnetized neutron star that might create these flashes.
Leung posits, “now the question was: How are you going to explain the presence of a magnetar inside this old, dead galaxy?”
Aiming telescopes at this radio burst
Once the spot was identified, colleagues turned optical telescopes to that region. What they saw did not match expectations.
Telescopes revealed a long-dead galaxy, lacking the active star factories known to give birth to the supermassive stars that collapse into magnetars.
A graduate researcher at McGill University in Montreal, Canada, named Vishwangi Shah refined the calculations used to confirm the bursts’ location.
“This is not only the first FRB to be found outside a dead galaxy, but compared to all other FRBs, it’s also the farthest from the galaxy it’s associated with,” Shah explained.
“The FRB’s location is surprising and raises questions about how such energetic events can occur in regions where no new stars are forming.”
Shah’s paper on this unusual fast radio burst, designated FRB 20240209A, was published in the Astrophysical Journal Letters on Tuesday, Jan. 21.
Pinpointing fast radio burst locations
Further progress in Leung’s FRB mapping mission came from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which has detected a large share of these bursts.
Its main array in British Columbia recently gained partner stations called outriggers, designed to sharpen its imaging abilities.
“When paired with the three outriggers, we should be able to accurately pinpoint one FRB a day to its galaxy, which is substantial. That’s 20 times better than CHIME, with two outrigger arrays,” Leung explained.
Using both optical and infrared telescopes
A new site at Hat Creek Observatory in Northern California is also online this week, raising hopes that astronomers can identify many more locations of similar bursts.
With these improvements, researchers can steer optical and infrared telescopes to the same spot in the sky. They can then figure out whether these bursts come from star clusters or distinct structures within a galaxy.
After Shah’s paper on FRB 20240209A was submitted, observers at the Green Bank Observatory in West Virginia, led by MIT’s Shion Andrew, used a second outrigger to verify the position of that newly discovered signal.
A related study by scientists at Northwestern University in Illinois, led by Einstein Postdoctoral Fellow Tarraneh Eftekhari, was also published that day.
Eftekhari said, “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,”
Explaining this radio burst
The presence of such a powerful burst in the outskirts of a silent elliptical galaxy hints at a new chapter in FRB studies.
“This result challenges existing theories that tie FRB origins to phenomena in star-forming galaxies,” Shah noted.
Because active star-forming regions are known breeding grounds for magnetars, this development opens the door to alternative ideas about how these bursts arise.
“The source could be in a globular cluster, a dense region of old, dead stars outside the galaxy. If confirmed, it would make FRB 20240209A only the second FRB linked to a globular cluster,” Shah concluded.
This galaxy stopped forming new stars long ago, yet the data point to a burst generated by something akin to a magnetar. If that scenario is correct, it might mean these exotic objects can emerge in places once deemed unlikely.
What happens next?
Researchers want to learn more about how an old galaxy could host events usually tied to younger environments. Leung sees huge promise in better pinpointing tools.
“CHIME and its outrigger telescopes will let us do astrometry at a level unmatched by the Hubble Space Telescope or the James Webb Space Telescope. It’ll be up to them to drill down to find the source. It’s an amazing radio telescope,” Leung enthusiastically concluded.
To sum it all up, what we learned is that astronomers still have a lot to learn about fast radio bursts. What causes them? Where do they come from?
As with most things in the universe, FRB answers are elusive, but that won’t keep us from continuing to ask the questions and doing the the work that it takes to find the answers, because that’s what science is all about.
The full study was published in The Astrophysical Journal Letters.
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