Artist's impression of a fast radio burst traveling from its source in a distant galaxy to an observed on Earth. Along this path, the burst passes through the halo of another galaxy, which affects the radio signal. Credit: ESO/M. Kornmesser; CC BY 4.0
The repeating fast radio burst FRB 20190520B traveled through an unusually large amount of matter on its journey to Earth. Could unidentified galaxy clusters in the billions of light-years that separate us from the burst’s source explain why?
The signal from the first fast radio burst ever detected. The highest frequencies arrive first, and the lower frequencies follow. Credit: Wikipedia user Psr1909; CC BY-SA 4.0
An Astrophysical Mystery
Fast radio bursts are among the most mysterious events in the universe. Most of these powerful, milliseconds-long radio blips occur just once, each burst an astronomical flash in the pan that leaves researchers puzzling over its origin. In rare cases, fast radio bursts repeat, giving us a clue that at least some sources of these mysterious bursts survive the event.
Snapshot of an interactive figure showing the locations of the newly identified galaxy clusters relative to FRB 20190520B’s location. You can interact with this figure here. Credit: Lee et al. 2023
Snapshot of an interactive figure showing the locations of the newly identified galaxy clusters relative to FRB 20190520B’s location. You can interact with this figure here. Credit: Lee et al. 2023
Surveying a Superlative Burst
The dispersion measure of the repeating fast radio burst FRB 20190520B is more than twice as large as expected given its distance. This unusually high value caught the attention of a team led by Khee-Gan Lee (Kavli Institute for the Physics and Mathematics of the Universe), which is carrying out the Fast Radio Burst (FRB) Line-of-sight Ionization Measurement From Lightcone AAOmega Mapping survey, or FLIMFLAM. This survey aims to map the distribution of luminous matter in the universe by searching for galaxy groups that are revealed by fast radio bursts.
The team spectroscopically determined the distances to galaxies in the field of view surrounding FRB 20190520B’s location and used a group-finding algorithm to identify galaxy groups and clusters. They found multiple galaxy groups in the field of view, including two galaxy clusters that lie directly between us and FRB 20190520B. By using models to estimate the masses of these galaxies and their halos, Lee’s team determined how much these intervening galaxy clusters contributed to the burst’s dispersion measure.
The team spectroscopically determined the distances to galaxies in the field of view surrounding FRB 20190520B’s location and used a group-finding algorithm to identify galaxy groups and clusters. They found multiple galaxy groups in the field of view, including two galaxy clusters that lie directly between us and FRB 20190520B. By using models to estimate the masses of these galaxies and their halos, Lee’s team determined how much these intervening galaxy clusters contributed to the burst’s dispersion measure.
A Revised Estimate
Based on FRB 20190520B’s extremely high dispersion measure, previous research estimated its host galaxy’s dispersion to be the highest of any known fast radio burst, a fact that has been difficult to reconcile with other observations of the galaxy. Now, with the new estimate of the foreground galaxies’ contribution, FRB 20190520B’s host galaxy has been assigned a more moderate value that aligns with its observational properties. This study demonstrates that even when focusing closely on a single fast radio burst, it’s still important to zoom out and consider the big picture!
Citation
“The FRB 20190520B Sight Line Intersects Foreground Galaxy Clusters,” Khee-Gan Lee et al 2023 ApJL 954 L7. doi:10.3847/2041-8213/acefb5
By Kerry Hensley
