When astronomers pointed some of the largest telescopes on Earth at the spot in Leo where a record-breaking radio burst had come from, they found nothing. The Keck telescope in Hawaii and the MMT Observatory in Arizona both came up empty. The researchers told Live Science the ground-based images “saw essentially nothing; it looked like empty sky.” The galaxy was there, but it was too faint for anything short of the James Webb Space Telescope.
Webb found it. In a paper published Oct. 8 in the journal Science, a team led by Manisha Caleb of the University of Sydney reported that the burst, named FRB 20240304B, came from a small, young galaxy whose light left it about 3 billion years after the Big Bang. That makes it the most distant fast radio burst ever traced to a home galaxy, at roughly twice the distance of the previous record holder.
A flash that lasts a few milliseconds
A fast radio burst is a pulse of radio waves that lasts a few thousandths of a second and, in most cases, never repeats. The first one was reported in 2007. Radio telescopes have since recorded thousands, but nobody has proved what produces them. “What makes fast radio bursts interesting is that we don’t know what generates them,” Caleb said in the ESA/Webb release announcing the result.
This one was picked up on March 4, 2024, by MeerTRAP, a burst-hunting instrument attached to the MeerKAT array of 64 radio dishes in South Africa. It lasted only milliseconds yet released more energy than the Sun puts out in a year, according to Sky & Telescope.
Astronomers can guess how far away a burst is before they find its galaxy. On the way to Earth, the radio waves pass through thin, hot gas between galaxies, and that gas slows the lower frequencies slightly more than the higher ones. The longer the delay across the band, the more gas the signal crossed and the farther it probably traveled. This burst arrived badly smeared, which pointed to a very long trip. A rough guess isn’t a measurement, though. Pinning down the distance meant finding the galaxy and measuring its redshift, the stretching of its light by the expansion of the universe.
Why Webb was the only way in
MeerKAT gave the team a very precise position, just southeast of the bright star Denebola. Archival images showed no galaxy there, and the follow-up at Keck and MMT didn’t either. Caleb and her collaborator Themiya Nanayakkara applied for director’s discretionary time on Webb, a reserve of observing time for urgent requests.
Webb’s Near-Infrared Camera picked out a 28th-magnitude dwarf galaxy at the burst’s position. Its Near-Infrared Spectrograph then measured the galaxy’s redshift at 2.148. Light from that far away has been traveling for about 11 billion years. Outlets have given the distance as anywhere from “more than 10 billion” to about 11 billion light-years, depending on which measure they use. The redshift is the number to go by.
The burst itself isn’t new. Caleb announced it at a conference in Montreal in July 2025, according to Sky & Telescope, and the team posted a version of the paper on the preprint server arXiv on Aug. 3, 2025. What changed this week is that the study passed peer review and appeared in Science, which lifted the embargo on coverage.
How far bursts have been traced
The new record makes more sense next to the milestones before it. Here are the steps that took fast radio bursts from an unexplained blip to a tool for measuring the universe.
| When | Milestone | Distance or reach |
|---|---|---|
| 2007 | First fast radio burst reported, by Duncan Lorimer’s team, in Science | Origin outside the Milky Way, galaxy unknown |
| April 2020 | A burst like those is caught from SGR 1935+2154, a magnetar inside the Milky Way | Our own galaxy |
| May 2020 | Jean-Pierre Macquart’s team uses six bursts to find the universe’s “missing” ordinary matter | Six bursts with known host galaxies |
| October 2023 | FRB 20220610A, found by Australia’s ASKAP, becomes the farthest traced burst | Redshift about 1, light 8 billion years old |
| October 2026 | FRB 20240304B published in Science | Redshift 2.148, about 11 billion years of light travel |
A galaxy too small for the theory
The record isn’t the most interesting part. The galaxy is.
Most galaxies that host fast radio bursts are big and actively forming stars. This one was about 1,000 times less massive than the team expected, the ESA/Webb release said. Laura Driessen of the University of Sydney, a member of the team, said in a statement quoted by Space.com that the galaxy was “surprisingly small, metal-poor and undergoing a very active episode of star formation.” Its rate of star formation suggests most of its stars may have formed within just 30 million years, according to the release. It existed during “cosmic noon,” the stretch of the universe’s history when galaxies were forming stars fastest.
That matters because there are two leading ideas about where bursts come from. One holds that they come from two neutron stars spiraling together and merging, a process that takes billions of years. If that were the main source, bursts should turn up in older galaxies with aging stars. The other holds that they come from magnetars, young neutron stars with extreme magnetic fields left behind when massive stars explode. Magnetars can form within a few million years of the stars that make them, so bursts would show up in young, busy galaxies like this one.
Caleb said in the release that the work makes a merger an improbable source for this burst. The 2020 burst from SGR 1935+2154 already showed that a magnetar can produce something close to a fast radio burst, at least nearby. This result supports magnetars as the source at a much earlier point in cosmic history. The finding is about the environment, not the object. Webb didn’t see a magnetar. It saw a galaxy where magnetars should be common.
Using bursts to weigh what’s between galaxies
The smearing that hinted at the burst’s distance is also why astronomers want more like it. For years, counts of the ordinary matter in the present-day universe came up short of what measurements of the early universe said should exist. “It was a bit of an embarrassment,” Macquart said in 2020, when his team used six bursts to show the missing matter was spread thinly between galaxies. The link between a burst’s delay and its distance is now called the Macquart relation. He died suddenly that June, at 45.
The 2023 record burst extended that test. Stuart Ryder of Macquarie University, who co-led that study, said in ESO’s release that it confirmed the relation “holds out to beyond half the known Universe.” FRB 20240304B pushes the test back across about 80 percent of cosmic history, the researchers write in the paper. Along the way, the signal also picked up the imprint of the Virgo Cluster and of a galaxy cluster about 3.5 billion light-years away that no one had known about.
Joeri van Leeuwen of ASTRON, the Netherlands Institute for Radio Astronomy, who was not involved in the study, called it a beautiful find. “Every large collection begins with just one specimen,” he told Sky & Telescope.
More where this came from
One burst can’t settle what causes the others, and the team doesn’t claim it does. In the preprint, the authors say the detection strengthens the case that most bursts go off soon after their parent stars form. Most is not all.
The team estimates MeerKAT could find and pin down several bursts a year from beyond redshift 1, more than halfway back to the Big Bang, and new radio telescopes should raise that number. The Square Kilometre Array Observatory has been building two such telescopes, in South Africa and Australia. Each distant burst will still need Webb or a telescope like it to find its galaxy.
Sources
- ESA/Webb, “Webb measures distance to farthest fast radio burst, suggesting origin” (Oct. 8, 2026). Used for: the redshift, the host galaxy’s mass and star formation, cosmic noon, the merger and magnetar comparison, Caleb’s quotes, the galaxy clusters along the path and MeerKAT’s expected detection rate.
- Sky & Telescope, “Fast Radio Burst Shatters Distance Record,” by Govert Schilling (Oct. 8, 2026). Used for: the energy, the dispersion explanation, MeerKAT’s dishes, the position near Denebola, Keck and MMT, the director’s discretionary time, the 28th-magnitude galaxy, the July 2025 announcement and van Leeuwen’s comments.
- Live Science, “James Webb telescope pinpoints the most distant ‘fast radio burst’ ever seen” (Oct. 8, 2026). Used for: the researchers’ description of the empty ground-based images and the “more than 10 billion light-years” figure.
- Space.com, “James Webb Space Telescope helps detect the most distant fast radio burst ever seen” (Oct. 8, 2026). Used for: Driessen’s description of the host galaxy.
- Caleb et al., “A fast radio burst from the first 3 billion years of the Universe,” arXiv preprint (Aug. 3, 2025). Used for: the detection date, the preprint timing, the merger and magnetar argument and the authors’ view on most bursts.
- ESO, “Astronomers detect most distant fast radio burst to date” (Oct. 19, 2023). Used for: FRB 20220610A, its 8-billion-year light travel time, Ryder’s quote, the Macquart relation and the Square Kilometre Array Observatory.
- ICRAR, release on Macquart et al. in Nature (May 2020). Used for: the missing-matter result and Macquart’s quote.
- International Astronomical Union, obituary of Jean-Pierre Macquart. Used for: his death on June 9, 2020, at 45.
- Bochenek et al., “A fast radio burst associated with a Galactic magnetar,” Nature (2020), arXiv version. Used for: the April 28, 2020 burst from SGR 1935+2154 and the 2007 first detection.