An international team using the James Webb Space Telescope has measured redshift 2.148 for fast radio burst FRB 20240304B — confirming it as the most distant precisely localized fast radio burst ever. Its light traveled some 10 to 11 billion years to reach us, meaning the burst erupted when the universe was only 3 billion years old. The study was published October 8 in the journal *Science*.
FRB 20240304B was detected on March 4, 2024, by the MeerTRAP project on South Africa's MeerKAT radio telescope array — 64 dishes of 13.5 meters each in the Great Karoo. It was a one-off, non-repeating millisecond flash of radio waves, and the radio data immediately suggested extreme distance.
Ground-based telescopes (Keck, MMT) saw nothing at the position. With director's discretionary time on Webb, the team found a 28th-magnitude faint galaxy about 0.3 arcseconds from the burst position; NIRSpec measured redshift 2.148 ± 0.001 — more than doubling the previous distance record.
Unexpectedly, the host galaxy is a small, clumpy, actively star-forming dwarf: a stellar mass of about 10 million suns (roughly 1,000 times less massive than expected), a star-formation rate of about 0.2 solar masses per year, and metallicity just 10 to 20% of the Sun's — most of its stars may have formed within just 30 million years. The team calculated a 97.5% probability that this galaxy is the true host.
"We thought it would be a big, nicely formed galaxy… and instead it was a little dwarf galaxy," said lead author Manisha Caleb of the University of Sydney.
Because the host galaxy's stars are so young, the neutron-star-merger origin model doesn't fit — binary neutron stars take at least a billion years to merge. The finding favors the young magnetar model: a magnetar born in the supernova collapse of a young massive star, whose "starquakes" release the burst.
The result proves astronomers can now identify and study fast radio bursts from the young universe.
The burst also acted as a "cosmic flashlight": its signal carried imprints of two intervening structures — a previously unknown galaxy cluster at redshift 0.3 (~3.5 billion light-years away) and the Virgo Cluster (~54 million light-years away) — letting astronomers trace the cosmic web.
"A fast radio burst is almost like a cosmic flashlight. It lights up everything along the path," said J. Xavier Prochaska of UC Santa Cruz.