In February 2024, scientists on Earth detected a powerful radio blast coming from space. Seeking to discover where it came from, they traced the brief flash of energy 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 previously thought that these fast radio bursts, which generate more energy in a single flare than our Sun generates in an entire year, were exclusively produced by young galaxies that regularly produce new stars. However, recent surveys, detailed in two sister studies published on January 21 in Letters from the astrophysical journal, encourage astronomers to reconsider the potential diversity of FRB sources.
Called FRB 20240209A, the February 2024 FRB was not just a one-off. Between February and July 2024, the same source erupted 21 times.
“The leading theory is that FRBs come from magnetars formed during supernova core collapses,” said Tarraneh Eftekhari of Northwestern University, who participated in both studies. statement. Magnetars are neutron stars with very powerful magnetic fields. And neutron stars are extremely small and dense celestial objects that are thought to form following the explosive death of certain large stars, i.e. supernovae.
“That doesn’t seem to be the case here,” Eftekhari continued. “As young massive stars end their lives as core-collapse supernovae, we see no evidence of young stars in this galaxy. With this new discovery, a picture is emerging that not all FRBs come from young stars. There may be a subpopulation of FRBs associated with older systems.
The ancient galaxy in question is 11.3 billion years old and 2 billion light years away. 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 one of the most massive galaxies there is.” Not only does the unusual FRB come from an ancient galaxy, but it also comes from the edge of that galaxy, specifically 130,000 light years from its center.
“Among the FRB population, this FRB is located furthest from the center of its host galaxy,” said Vishwagi Shah of McGill, who participated in both studies. “This is both surprising and exciting, because FRBs are expected to come from the interior of 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 are forming.
But FRB 20240209A is not the first FRB detected far from regions of active star formation: it is the second. In 2022, astronomers traced M81 FRB, located 12 million light years from Earth, to a star cluster on the edge of the Messier 81 galaxy.
FRB 20240209A “could be a twin of the M81 event (M81 FRB). It is far from its home galaxy (far from the birthplace of stars) and the population of stars in its home galaxy is extremely old. She had her glory days and is now retiring,” said Wen-fai Fong of Northwestern University, who participated in both studies. “At the same time, this type of ancient environment is causing us to rethink our standard models of FRB progenitors and look to more exotic formation channels, which is exciting.”
One of the studies suggests that, like M81 FRB, the new FRB could also come from a cluster of stars, called a globular cluster.
“A globular cluster origin for this repeating FRB is the most likely scenario to explain why this FRB is located outside its host galaxy,” Shah explained. “We do not know for sure if there is a globular cluster present at the FRB location and have submitted a proposal to use the James Webb Space Telescope for follow-up observations of the FRB location. If so, this would make this FRB the second FRB known to reside in a globular cluster. Otherwise, we should consider other exotic scenarios for the origin of the FRB.”
In other words: back to the drawing board!