The farthest fast radio burst is older than Earth and doubles the distance record

A fast radio burst, a flash of radio waves lasting a few thousandths of a second, left its source when the universe was about 3 billion years old and reached a telescope in South Africa more than 10 billion years later. It is the most distant fast radio burst ever traced to a home galaxy, at more than twice the distance of the previous record holder. The flash set out more than five billion years before Earth formed.

The surprise came when the James Webb Space Telescope found where it came from. Astronomers expected a large, mature galaxy. Instead the source is a faint dwarf, roughly 1,000 times less massive than the team anticipated, that seems to have built most of its stars in a short, violent burst. That small, young home is now one of the strongest clues yet to what produces these flashes.

Thousands of fast radio bursts have been detected, but only about a hundred have been pinned to a specific galaxy, and almost all of those sit relatively close to us. The new burst, catalogued as FRB 20240304B, pushes that map into the busiest era of star formation in cosmic history.

“What makes fast radio bursts interesting is that we don’t know what generates them,” said Manisha Caleb of the University of Sydney, who led the study. “We have theories for what objects produce them, but we don’t have conclusive proof.”

How a radio dish and Webb found a galaxy nobody could see

The burst was caught by MeerKAT, an array of 64 radio dishes in South Africa’s Karoo. A search system called MeerTRAP, led by Ben Stappers of the University of Manchester, scans its data in real time for single bright pulses. This one stood more than 100 times above the background noise, and the array fixed its position to a fraction of an arcsecond, in the constellation Leo.

The first hint of its distance came from the signal itself. Radio waves crossing the thin gas between galaxies slow down slightly, and lower frequencies slow down more, so a burst arrives as a sweep from high to low pitch. Astronomers call the size of that delay the dispersion measure. For this burst it was about 2,458 units, far higher than most known bursts, and a sign the signal had crossed an enormous column of gas.

That number only gives a rough distance. A real one needs the host galaxy and its spectrum, and archival sky surveys showed nothing at the position. Neither did an hour of deep imaging with the Keck I telescope in Hawaii or infrared images from the MMT Observatory in Arizona. The galaxy was too faint for the largest ground-based telescopes.

So the team requested time on Webb. Its Near-Infrared Camera picked out a 28th-magnitude smudge about 0.3 arcseconds from the burst’s position, and a statistical test gave a 97.5% probability that the burst came from it. Webb’s Near-Infrared Spectrograph then caught light from glowing hydrogen and oxygen in the galaxy, stretched by the expansion of the universe to a redshift of 2.148. That places the burst in the period astronomers call cosmic noon, when galaxies were forming stars faster than at any time before or since.

What the record means in numbers

The previous record holder, a burst caught by Australia’s ASKAP telescope, sat at a redshift of about 1.016, and its light had travelled roughly 8 billion years. The new burst more than doubles that redshift. In the paper’s words, the signal “probes ionized gas over approximately 80% of cosmic history.”

The energy sits at the top of the range seen for these events. Sky & Telescope put it in familiar terms: more energy than the Sun gives off in a year, packed into a flash shorter than a blink.

The host galaxy is the strangest part. The team’s estimate puts its stellar mass on the order of 10 million times the mass of the Sun, a tiny fraction of the Milky Way’s stars. Its gas holds only about 10 to 20% of the Sun’s share of elements heavier than helium, and it is forming stars far faster than a galaxy its size normally would. The researchers estimate that most of its stars may have formed within about 30 million years.

“We thought it would be a big, nicely formed galaxy with lots of stars,” Caleb said. Stappers was blunter: “The host sticks out in the whole galaxy sample that we have. And it was not what we were expecting.”

Why a small, young galaxy points to one culprit

The two leading explanations make different predictions about where bursts should appear. One says they come from magnetars, neutron stars with magnetic fields billions of times stronger than the strongest magnets built on Earth, born when massive stars collapse. Those form within a few million years of the stars that make them. The other says some bursts come from collisions of neutron stars, which can take billions of years to spiral together and so tend to occur in older galaxies.

A galaxy that built itself in a few tens of millions of years leaves little room for the slow option. “Our work suggests that it’s very unlikely that this FRB was produced by a merger,” Caleb said. Metal-poor gas also tends to produce more very massive stars, which are the kind that leave magnetars behind. In our own galaxy, the magnetar SGR J1935+2154 has already produced weak bursts of the same kind.

The signal also carried a record of everything it passed through. Its path crosses the Virgo Cluster, the giant group of galaxies about 54 million light-years away, and runs close to a previously unknown group of galaxies at a redshift of 0.31, about 3.5 billion light-years from us. The team estimates those two structures account for most of the extra delay in the signal.

What it doesn’t settle

One burst is one data point. The magnetar link is the most natural reading of this host galaxy, but the researchers stress it is not proof, and it does not mean every fast radio burst has the same origin.

The galaxy’s properties come with wide error bars. Its mass, metal content and star-formation history are model estimates drawn from a few Webb images and one spectrum of an object at the limit of detection. Very few burst hosts this faint have been studied at any distance, so it is hard to say whether this galaxy is unusual or simply the first of a kind earlier surveys missed.

The team argues the find was not a fluke. MeerKAT is currently the only burst-hunting instrument sensitive enough to see this far, and they predict that about 6.3% of the bursts in its main survey should come from beyond a redshift of 2. Only more detections will test that. “Every large collection begins with just one specimen,” said Joeri van Leeuwen of the Netherlands Institute for Radio Astronomy, who was not involved in the work.

Common questions about the most distant fast radio burst

What is a fast radio burst?

A fast radio burst is a flash of radio waves that lasts a few milliseconds and can carry, in the brightest cases, as much energy as the Sun emits in a year. The first was found in 2007. Their source is still debated.

How far away is the most distant fast radio burst?

FRB 20240304B sits at a redshift of 2.148. Its signal travelled for more than 10 billion years and left its galaxy when the universe was about 3 billion years old. That is more than double the redshift of the previous record holder.

Do magnetars cause fast radio bursts?

Magnetars are the best-supported explanation, and the young, star-forming host of this burst strengthens that case. But no study has proven that every burst comes from a magnetar, and the researchers behind this result say there is no conclusive proof yet.

What comes next

The burst was detected on March 4, 2024, first presented at a conference in Montreal in July 2025, and published in the journal Science on October 8, 2026. The team estimates that MeerKAT can find and pinpoint several bursts per year from more than halfway back to the Big Bang, with Webb needed to identify their faint host galaxies. The Square Kilometre Array’s mid-frequency telescope, now under construction in South Africa, is expected to push that search further. Stappers set the target plainly: “The next step is to push this frontier further and see how close we can get to the first generations of stars.”

Reference: Caleb et al., “A fast radio burst at redshift 2, three billion years after the Big Bang,” Science, 2026. DOI: 10.1126/science.adz2675

Tags: astronomy, James Webb Space Telescope, magnetar, MeerKAT, fast radio burst, FRB 20240304B