
Example of a signal from a nearby fast radio burst. The top panel shows the overall intensity over time, while the bottom panel shows the frequency of the burst over time. [Adapted from Bhardwaj et al. 2024]
Mysterious Bursts
Fast radio bursts are powerful, milliseconds-long flashes of radio waves of unknown origin. Since the first fast radio burst was discovered in 2007, astronomers have detected roughly a thousand of these mysterious signals. The source of these bursts is still up for debate, with supernovae, magnetars, colliding objects, and other energetic phenomena tapped as candidates.
To understand the origin of these bursts, it helps to know what kind of galaxies they happen in. If fast radio bursts emerge from spiral galaxies with active star formation, it could mean that the bursts are linked to “prompt” formation channels such as the deaths of short-lived massive stars. If instead bursts come from elliptical galaxies with little or no star formation, that could imply that bursts come from “delayed” channels like the slowly progressing mergers of stellar remnants. So, what kind of galaxies do fast radio bursts tend to come from?
In the Neighborhood
Mohit Bhardwaj (Carnegie Mellon University and McGill University) and collaborators turned to data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) to answer this question. Their aim was to study fast radio bursts in the local universe since a sample of nearby bursts is less likely to be affected by observational biases. To find nearby bursts, Bhardwaj’s team searched the first CHIME fast radio burst catalog for signals with low dispersion measure. On average, the farther the source, the larger the dispersion measure — essentially, because there’s more stuff in between the source and Earth to disperse the radio signal.

Visible-light images of the localization regions of the four fast radio bursts in this study. The red boxes indicate the most likely host galaxy for each burst. Note that FRB 20181223C has four potential host galaxies (red and cyan boxes in the upper-left image), but only one that satisfied the source’s maximum redshift limit. Click to enlarge. [Bhardwaj et al. 2024]
A Spiral Sample
Including the four bursts with newly identified host galaxies from this work, researchers have now localized the positions of 18 nearby fast radio bursts. What ties these burst-hosting galaxies together, if anything? As it turns out, they’re all spiral galaxies. That’s an intriguing result, but does it necessarily mean that fast radio bursts are more likely to come from spiral galaxies, or is it just easier to detect fast radio bursts from spiral galaxies?

The host galaxies of all 18 local universe fast radio bursts used in this study. Click to enlarge. [Bhardwaj et al. 2024]
Bhardwaj’s team noted that this doesn’t mean all fast radio bursts must come from supernovae; because a small number of known bursts have arisen in unusual locations like globular clusters and non-star-forming spiral galaxies, delayed pathways like mergers of stellar remnants may be responsible for certain bursts.
Citation
“Host Galaxies for Four Nearby CHIME/FRB Sources and the Local Universe FRB Host Galaxy Population,” Mohit Bhardwaj et al 2024 ApJL 971 L51. doi:10.3847/2041-8213/ad64d1