Farthest Fast Radio Burst Traced to a Tiny Galaxy by Webb

A Millisecond Flash From 10 Billion Years Ago, Traced to a Tiny Galaxy

For a few thousandths of a second, something in a faraway galaxy blazed in radio waves — then it was gone. By the time that flash reached a radio telescope in South Africa on 4 March 2024, it had been travelling for more than 10 billion years. It had set out when the universe was only about 3 billion years old.

Now astronomers know where it came from. On 8 October 2026, ESA and NASA announced that the NASA/ESA/CSA James Webb Space Telescope had pinpointed the host galaxy of the most distant fast radio burst (FRB) seen to date, in a study published that day in the journal Science. The burst is called FRB 20240304B.

What is a fast radio burst?

Fast radio bursts were first discovered in 2007. They are enigmatic, millisecond-long flashes of radio emission from the distant universe, and their origin remains uncertain — particularly because most are seen once and never again. A flash that lasts a few milliseconds yet can be detected across billions of light-years must come from an extremely energetic event. The question is: what kind?

The MeerTRAP team used South Africa’s MeerKAT telescope to detect FRB 20240304B, and the radio data suggested it was extremely distant, possibly the most distant yet. But to confirm the distance, astronomers needed its host galaxy — and the world’s largest ground-based telescopes could not see any galaxy at that spot in the sky. Only Webb could detect and characterise it.

A galaxy 1,000 times less massive than expected

Webb’s NIRCam instrument detected a galaxy in the right location, and its NIRSpec instrument measured the galaxy’s redshift: 2.148, corresponding to a time just 3 billion years after the Big Bang. The vast majority of fast radio bursts detected to date occurred billions of years later in cosmic history.

The galaxy itself was a surprise. Most galaxies known to host fast radio bursts are massive, star-forming galaxies. This one was 1,000 times less massive than the team expected: a little dwarf galaxy, although it was actively forming stars.

“We thought it would be a big, nicely formed galaxy with lots of stars, and instead it was a little dwarf galaxy, although it was actively forming stars,” said Manisha Caleb of the University of Sydney, the study’s lead author.

The galaxy existed at the height of “cosmic noon”, a period when star formation across the universe was at its peak, and its rate of star formation suggested most of its stars may have formed within just 30 million years.

Why a young galaxy points to magnetars

The host’s youth matters because it helps test two ideas about where fast radio bursts come from. One idea says they come from the merger of two neutron stars. That process takes billions of years, as the stars slowly spiral together — so bursts from mergers would be expected in older galaxies with more evolved stars.

The other idea says a burst can come from a single, young, highly magnetic neutron star called a magnetar, perhaps through starquakes. A magnetar forms when a massive star explodes, so a burst could follow relatively quickly, with no large time delay — and would be expected in younger galaxies like this one.

“Our work suggests that it’s very unlikely that this FRB was produced by a merger,” said Caleb. The result does not prove that all fast radio bursts come from magnetars, but it strengthens the case that at least some do, and that they were already happening in small, young galaxies early in cosmic history.

The burst also acted like a cosmic flashlight on its long journey: it carried the imprint of two cosmic structures it passed through, including a previously unknown galaxy cluster and the nearby Virgo Cluster, showing how distant bursts can help map the invisible “cosmic web” of matter between galaxies.

If your child looks up at the night sky and asks how we know anything about objects billions of light-years away, astronomy and physics together give the answer — light, redshift, telescopes and patient detective work. Book your first lesson and compare verified science and physics tutors, online, in person or in a group class.

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