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Astronomers have identified the most distant fast radio burst (FRB) localized to a host galaxy so far. The burst, named FRB 20240304B, was detected by South Africa’s MeerKAT radio array on 4 March 2024. Webb identified the galaxy it came from and measured that galaxy’s distance, placing the burst at a redshift of 2.148. That corresponds to a time when the universe was about 3 billion years old, even though the radio signal spent more than 10 billion years travelling to Earth. The findings were published in Science on 8 October 2026.
What a fast radio burst is
A fast radio burst is a flash of radio waves that lasts only milliseconds. Astronomers have detected thousands of them since the first was reported in 2007, but most are seen once and never again, so their origin remains unknown. Several kinds of objects have been proposed as sources, and the lead author of the new study, Dr. Manisha Caleb of the University of Sydney, has put the situation plainly in the NASA Webb mission release of 8 October 2026: “What makes fast radio bursts interesting is that we don’t know what generates them. We have theories about what objects produce them, but we don’t have conclusive proof.”
Because the signal is so brief, the best way to learn about an FRB is to pinpoint where it came from. Once a burst is tied to a specific galaxy, its distance and the properties of that galaxy can be measured. That is the step FRB 20240304B finally made possible at a greater distance than any previous localized burst.
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How MeerKAT caught the burst
The burst was detected by the MeerTRAP team using MeerKAT, an array of radio dishes in South Africa’s Karoo region. MeerTRAP is a project designed to find short radio transients, and its detection on 4 March 2024 was the starting point for the study. The radio data gave two things: a precise position on the sky, and measurements suggesting the burst might be exceptionally distant.
That position was the key limitation, not a dead end. Radio localization narrows the search to a small patch of sky, but it does not say which galaxy in that patch produced the burst. In this case, ground-based telescopes could not find a host galaxy at the location, so the team turned to Webb.
How Webb found and measured the host galaxy
Webb’s role was to identify and characterize the galaxy, not to detect the radio burst. The work happened in two stages, described in the University of California, Santa Cruz release and the Science paper:
- Imaging with NIRCam. Webb’s Near-Infrared Camera detected a galaxy at the position supplied by the radio localization. This turned a patch of sky into a specific candidate host.
- Spectroscopy with NIRSpec. Webb’s Near-Infrared Spectrograph split the galaxy’s light into its component wavelengths. The team used this spectrum to measure the galaxy’s redshift, which is how much its light has been stretched by the expansion of the universe.
The redshift came out to 2.148, with an uncertainty of ±0.001 given in the Science paper’s abstract. Because the burst and its host are at the same distance, that single measurement sets the epoch of the burst itself.
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What “ancient” means in this story
The word “ancient” can be misread, so it helps to separate the two clocks involved. One measures when the burst happened, and the other measures how long its signal took to arrive.
Rank #3
| Measure | Value | Source and qualification |
|---|---|---|
| Detection date | 4 March 2024 | MeerKAT observation reported by the MeerTRAP team and university announcements in 2026 |
| Host galaxy redshift | 2.148 (±0.001) | Webb NIRSpec measurement given in the Caleb et al. Science paper abstract |
| Cosmic epoch of the burst | About 3 billion years after the Big Bang | NASA Webb mission team and the Science study; describes when the burst occurred |
| Signal travel time | More than 10 billion years | Stated in the coverage of the study; describes how long the radio waves took to reach Earth |
The gap between those last two rows is the point of the story. The light and radio waves left the source when the universe was young, and they have been travelling through an expanding universe ever since. The redshift is a measure of how far the universe has expanded during that trip, not a distance you can convert straightforwardly into light-years, so this article does not give a light-year figure for the source.
“Most distant known” is a claim tied to the 8 October 2026 report. Other localized bursts may be found at greater redshifts, and the record should be checked against newer publications.
What the host galaxy looks like
The host is a low-mass dwarf galaxy that is clumpy in structure and actively forming stars. Its size and youth surprised the team. Professor Ben Stappers, MeerTRAP project leader and co-author, said in the University of Oxford Department of Physics announcement: “The host sticks out in the whole galaxy sample that we have. And it was not what we were expecting.”
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Why the burst is useful beyond the galaxy
Radio signals are altered as they pass through plasma, the electrically charged gas that fills the space between galaxies. An FRB crossing that gas arrives with its signal changed in measurable ways. That makes a localized burst a possible probe of ionized matter, including the diffuse material between galaxies that is hard to observe directly.
The paper reports two consequences of the localization. First, it extends the redshift reach of localized FRBs roughly twofold. Second, the team says it allows the probing of ionized baryons across about 80% of cosmic history. This is a statement about what future localized bursts can reach, not a finding that this single burst has mapped that matter. One burst can contribute to that effort, but it does not complete it.
What is still unknown
- The physical source of FRB 20240304B is not identified. The host’s properties constrain theories but do not name the mechanism.
- Most FRBs have not been localized, so this single host cannot stand in for the whole population.
- The redshift record is specific to the 8 October 2026 report and may be surpassed.
For readers who want the primary material, the study is the Science paper by Caleb et al., DOI 10.1126/science.adz2675, with an earlier preprint posted on arXiv as 2508.01648 on 3 August 2025. The NASA Webb mission team, ESA/Webb, the University of Sydney, the University of California, Santa Cruz, and the University of Oxford Department of Physics each published releases on 8 October 2026 that describe different parts of the work.
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