Astronomers using the James Webb Space Telescope have identified the host galaxy of the farthest fast radio burst ever recorded, tracing a millisecond-long pulse of radio waves back across 11 billion years of cosmic history, researchers announced in a study published Thursday in the journal Science.
The burst, designated FRB 20240304B, was initially captured on March 4, 2024, by the MeerKAT radio telescope array in South Africa. Measurements showed the signal was emitted when the universe was only about three billion years old, more than doubling the distance of the previous record holder.
Fast radio bursts are fleeting but exceptionally powerful flashes of radio energy from deep space. While they last only a fraction of a second, they can unleash as much energy as the sun produces over months or even years. Because the world’s largest ground observatories could detect no visible host at the coordinates of the burst, astronomers turned to Webb to find its point of origin.
An unexpected cosmic nursery
Using its Near-Infrared Camera and Near-Infrared Spectrograph, Webb pinpointed a galaxy at a redshift of 2.148, confirming its extreme age and distance. However, the physical traits of the host caught scientists off guard.
Previous fast radio bursts have typically originated in massive, mature galaxies. In this case, Webb revealed a metal-poor dwarf galaxy roughly 1,000 times less massive than expected, existing during a period known as “cosmic noon,” when star creation across the universe reached its peak. Researchers estimated that most of the galaxy’s stars took shape within a narrow window of roughly 30 million years.
“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,” lead author Manisha Caleb of the University of Sydney said in a statement released by NASA.
Clues to a violent origin
The discovery provides critical evidence for resolving how these enigmatic cosmic pulses are born. Scientists have debated whether fast radio bursts stem from colliding neutron stars or from magnetars—dense neutron stars possessing exceptionally intense magnetic fields that form after massive stars explode in supernovas.
Collisions between two neutron stars take billions of years to unfold, meaning they should occur primarily in older, well-developed galaxies. Because the newly observed host galaxy is remarkably young and formed its stars rapidly, the researchers concluded the pulse likely came from a young magnetar created in a recent stellar explosion.
“Our work suggests that it’s very unlikely that this FRB was produced by a merger,” Caleb said.
Probing invisible cosmic matter
Beyond clarifying the mechanism behind the burst, the signal served as a high-speed probe of the space between galaxies. As radio waves traverse the cosmos, they interact with sparse gas and dust, slowing down slightly and preserving a record of the matter they encounter along the way.
In this case, the burst traveled through roughly 80 percent of cosmic history before reaching Earth. Analysis of the signal revealed the imprint of two intervening structures: an uncataloged galaxy cluster roughly 3.5 billion light-years from Earth and the nearby Virgo Cluster, situated about 54 million light-years away, NASA reported.
Whether FRB 20240304B was an isolated flash or will produce repeat pulses remains unknown. Researchers with the MeerTRAP project estimate that the MeerKAT array could detect several distant bursts each year as observing techniques improve, with Webb expected to play an essential role in confirming their origins.
