In February 2024, scientists on Earth detected a powerful radio burst from space. Wanting to find out where it came from, they follow a brief flash of energy back to its extraterrestrial source—and find something unexpected.
Scientists led by Northwestern University and McGill University have followed a fast radio burst (FRB) to the edge of an ancient elliptical galaxy. Scientists previously thought that these rapid radio bursts, which produce more energy in a single flare than our Sun produces in an entire year, were only produced by small galaxies that slowly churn out new stars. The latest investigation, however, is detailed in two sister studies published on January 21st The Astrophysical Journal Letters, they encourage astronomers to reconsider the possible diversity of FRB sources.
Called FRB 20240209A, the February 2024 FRB was no fluke. Between February and July 2024, the same fountain ignited 21 times.
“The prevailing view is that FRBs from magnetars are formed by core-collapse supernovae,” Tarraneh Eftekhari of Northwestern University, who participated in both studies, said in a university statement. Clusters are magnetized neutron stars—and neutron stars are very small and dense celestial bodies that are thought to form after the death of massive stars, i.e., supernovae.
“That doesn’t seem to be the case here,” Eftekhari continued. “Although young, massive stars end their lives as core supernovae, we see no evidence of young stars in this galaxy. Thanks to these new findings, a picture emerges that shows that not all FRBs come from small stars. There are probably a small number of FRBs associated with older systems.”
The oldest galaxy in question is 11.3 billion years old, and 2 billion lightyears away from us. Using computer simulations, Eftekhari and his colleagues found that the galaxy is extremely luminous, and 100 billion times more massive than our Sun.
“It appears to be the largest FRB host galaxy so far,” Eftekhari said. “It’s among some of the largest galaxies in existence.” Not only did the unusual FRB appear in an old galaxy, it also appeared at the edge of that galaxy—specifically, 130,000 lightyears from its center.
“Among the FRB people, this FRB is available [farthest] from the center of its galaxy,” said Vishwangi Shah of McGill, who participated in both studies. “This is surprising and exciting, as FRBs are expected to originate within galaxies, usually in star-forming regions. The FRB’s location so far outside its galaxy raises questions about how these powerful events can occur in regions where no new stars are forming.”
But FRB 20240209A is not the first FRB to be detected far from active star-forming regions—it is the second. In 2022, astronomers tracked the M81 FRB, located 12 million light-years from Earth, to the galaxy’s edge cluster Messier 81.
FRB 20240209A “may be the twin event of M81 [M81 FRB]. It is far from the home galaxy (far from where any stars are born), and the number of stars in the home galaxy is very old. It had its heyday and now it’s about to retire,” said Wen-fai Fong from Northwestern University, who participated in both studies. “At the same time, this type of primitive environment makes us rethink our standard FRB models and turn to channels of unusual, exciting formations.”
Some research suggests that, like the M81 FRB, the new FRB may have originated from a cluster of stars, called a globular cluster.
“The globular cluster origin of this recurring FRB is a possible explanation for why this FRB is outside its galaxy,” Shah explained. “We don’t really know if there is a global cluster in the FRB region and we have submitted a proposal to use the James Webb Space Telescope to follow up on the FRB region. If so, it would make this FRB only the second FRB known to reside in the globular cluster. If not, we will have to consider other rare cases of FRB origin.”
In other words: back to the drawing board!
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