MeerKAT and Webb trace the most distant fast radio burst to a small galaxy at redshift 2.15

The team knew the burst was far away before they had seen anything at its position. The radio signal arrived heavily dispersed, and that alone pointed to a distant source ^[4]. Deep searches with powerful ground-based telescopes then "saw essentially nothing; it looked like empty sky," the researchers told Live Science ^[10]. "The most likely explanation was that the galaxy was simply too faint to be detected in those observations. That is where JWST became transformative," they wrote ^[11].

The JWST time came through Director's Discretionary Time, a route meant for time-sensitive observations. The first step was a very deep image with the Near Infrared Camera ^[12]. "Suddenly, there it was: a very faint galaxy almost exactly where we expected the host of the FRB to be," Nanayakkara said ^[13].

I like the design. The position and the distance come from different instruments measuring different things. MeerKAT supplied "a very precise position on the sky," in Nanayakkara's words ^[2]. The dispersion depends on the material the signal crossed on its way here ^[16]. The spectral lines measure something else: how far the expansion of the universe has stretched light of known laboratory wavelength. JWST's spectrograph found hydrogen and oxygen lines, and their shift gave a redshift of about 2.15 ^[14]. "We are therefore seeing this galaxy as it was when the universe was only around three billion years old, so roughly one-fifth of its current age," Nanayakkara said ^[15]. Neither account reports how likely it is that an unrelated faint galaxy would sit that close to the burst position by chance.

FRB 20240304B more than doubles the previous FRB distance record ^[3]. That record was set in 2023 by a burst whose discovery also involved University of Sydney astronomers ^[9].

JWST also showed the host was smaller than expected, metal-poor and forming a lot of stars ^[5]. "The galaxy hosting this burst is surprisingly small, metal-poor and undergoing a very active episode of star formation," said Laura Driessen, a co-author at the University of Sydney ^[6]. Magnetars are highly magnetised neutron stars formed when massive stars explode. The team argues that a young, vigorously star-forming galaxy fits magnetar formation better than mergers of older neutron stars ^[7].

Astronomers have detected thousands of fast radio bursts ^[8]. This is one host, and the team limits its claim to at least some of them ^[7]. I think the magnetar point holds for this burst and goes no further. One galaxy at redshift 2.15 cannot say what share of all FRBs come from magnetars.

"Once our radio telescopes find and localize a suitable new source, we can trigger the JWST observations," Nanayakkara said ^[18]. So the number of hosts this distant depends first on radio arrays localizing bursts, then on getting JWST time ^[12]. Caleb said, "What is particularly exciting about our result is that we've now demonstrated that we can identify and study an FRB from when the universe was young." ^[17] Ben Stappers of the University of Manchester, principal investigator of MeerTRAP, said "The next step is to push this frontier further and see how close we can get to the first generations of stars." ^[19]