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First discovered in 2007, fast radio bursts are enigmatic, millisecond-long flashes of radio emission from the distant universe. Their origin remains uncertain, particularly since most are seen once and never again. Astronomers using NASA’s James Webb Space Telescope have pinpointed the host galaxy of the most distant fast radio burst (FRB) seen to date. Their finding has implications for what kind of energetic event creates these bursts.

“What makes fast radio bursts interesting is that we don’t know what generates them. We have theories for what objects produce them, but we don’t have conclusive proof,” said Manisha Caleb of the University of Sydney, lead author on the study published Thursday in the journal Science .

The MeerTRAP team used the MeerKAT telescope to detect the burst on March 4, 2024, leading to its designation as FRB 20240304B. The radio data from this burst suggested that it was extremely distant, possibly the most distant one seen to date. To confirm that distance, though, astronomers would need to study its host galaxy. Although they knew the location of the FRB very precisely, the world’s largest ground-based telescopes could not see any galaxy at that spot in the sky. As a result, the team turned to the Webb telescope.

Webb’s NIRCam (Near-Infrared Camera) instrument detected a galaxy in the right location, and its NIRSpec (Near-Infrared Spectrograph) instrument provided a precise measurement of the galaxy’s redshift : 2.148, corresponding to a time just 3 billion years after the big bang. The vast majority of FRBs detected to date occurred billions of years later in cosmic history.

The team discovered that the host galaxy of FRB 20240304B was not typical of other galaxies with FRBs. Most FRB galaxies are massive star-forming galaxies, but the galaxy they found was 1,000 times less massive than they expected.

“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 Caleb.

“The host sticks out in the whole galaxy sample that we have. And it definitely was not what we were expecting,” said Ben Stappers of the University of Manchester, United Kingdom, a co-author on the paper. “This combination of using the MeerTRAP project on the MeerKAT telescope to discover and localize these distant bursts and Webb to study their hosts is very exciting.”