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In February 2024, Earth scientists detected a powerful burst of radio from outer space. Trying to find out where it came from, they traced the brief flash of energy back to its extraterrestrial source – and discovered something unexpected.
Scientists led by Northwestern University and McGill University have traced a fast radio burst (FRB) to the edges of an ancient elliptical galaxy. Scientists had previously thought that these fast radio bursts, which generate more energy in a single flare than our Sun generates in an entire year, are produced exclusively by young galaxies that are steadily producing new stars. Recent investigations, however, detailed in two sister studies published on January 21 in The Astrophysical Journal Letters, prompt astronomers to reconsider the potential diversity of FRB sources.
Dubbed FRB 20240209A, the February 2024 FRB wasn’t just a fact. Between February and July 2024, the same source exploded 21 times.
“The prevailing theory is that FRBs come from magnetars formed by core-collapse supernovae,” Tarraneh Eftekhari of Northwestern University, who participated in both studies, said in a statement. declaration. Magnetars are neutron stars with very powerful magnetic fields – and neutron stars are extremely small, dense celestial objects that are thought to form following the explosive death of some large stars, i.e. supernovae.
“That doesn’t seem to be the case here,” Eftekhari continued. “While young, massive stars end their lives as core-collapse supernovae, we see no evidence of young stars in this galaxy. Thanks to this new discovery, a picture is emerging that shows that not all FRBs come from young stars. Perhaps there is a subpopulation of FRBs that are associated with older systems.”
The old galaxy in question is 11.3 billion years old, and 2 billion light years away from us. Using computer simulations, Eftekhari and his colleagues discovered that the galaxy is extremely bright, and 100 billion times more massive than our Sun.
“It appears to be the most massive FRB host galaxy to date,” Eftekhari said. “It’s among some of the most massive galaxies out there.” Not only did the unusual FRB originate from an old galaxy, it also came from the edge of that galaxy, specifically, 130,000 light years from its center.
“Among the FRB population, this FRB is located the (farthest) from the center of its host galaxy,” said McGill’s Vishwangi Shah, who participated in both studies. “This is both surprising and exciting, since FRBs are expected to originate in galaxies, often in star-forming regions. The location of this FRB so far outside its host galaxy raises questions about how such energetic events can occur in regions where no new stars form.
But FRB 20240209A isn’t the first FRB to be detected far from active star-forming regions—it’s the second. In 2022, astronomers traced M81 FRB, which is 12 million light years from Earth, to a cluster of stars on the edge of the Messier 81 galaxy.
FRB 20240209A “could be a twin of the event M81 (M81 FRB). It is far from its home galaxy (far from where any stars are born), and the population of stars in its home galaxy is very old. It has had its day and is now in retirement,” said Wen-fai Fong of Northwestern University, who participated in both studies. “At the same time, this kind of old environment makes us rethink our standard FRB progenitor models and turn to more exotic formation channels, which is exciting.”
One of the studies suggests that, like M81 FRB, the new FRB could also have originated from a cluster of stars, called a globular cluster.
“A globular cluster origin for this repetitive FRB is the most likely scenario to explain why this FRB is located outside its host galaxy,” explains Shah. “We do not know for a fact if there is a globular cluster present at the FRB location and we have submitted a proposal to use the 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 origin of FRBs.
In other words: back to the drawing board!
