On March 4 2024, South Africa’s MeerKAT radio telescope caught a split‑second burst of radio waves, later named FRB 20240304B. The signal travelled more than 10 billion years, making it the most distant fast radio burst ever recorded.

After initial attempts with the world’s largest ground‑based telescopes failed to pinpoint its origin, the team led by Manisha Caleb and Themiya Nanayakkara of the University of Sydney turned to NASA’s James Webb Space Telescope. JWST revealed that the burst came from a faint dwarf galaxy that existed when the universe was only about three billion years old.

That dwarf galaxy is tiny – roughly 1,000 times less massive than the typical galaxies that host FRBs – and it is actively forming new stars. Its low heavy‑element content and youthful nature match the conditions expected for magnetars, the highly magnetised neutron stars thought to produce “starquakes” that generate fast radio bursts.

The burst’s radio signal also acted like a cosmic flashlight, carrying an imprint of the matter it passed through. Analysis of the signal uncovered a previously unknown galaxy cluster about 3.5 billion light‑years away, and it even picked up the much nearer Virgo cluster.

"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," Caleb said. Co‑author J. Xavier Prochaska of the University of California, Santa Cruz added, "A fast radio burst is almost like a cosmic flashlight; it lights up everything along the path."

Because FRB 20240304B can be traced back to such an early epoch, astronomers now have a new tool for probing the young universe. By studying how these bursts travel through intervening matter, researchers can map distant structures and test ideas about the origins of FRBs themselves.