Oldest fast radio burst ever seen sheds light on early star formation

A strange flash of light from near the beginning of the universe could help astronomers map difficult-to-see gas in between galaxies, like a flashbulb in a dark room.

Fast radio bursts (FRBs) are extremely short but powerful blasts of radio-frequency light that have puzzled astronomers since they were first spotted in 2007. A leading theory is that they are produced by extremely magnetic neutron stars, called magnetars. But because we only know of a few thousand examples in the whole universe, with most coming from galaxies that are relatively close to the Milky Way, there is much we still don’t understand about them.

Now, Manisha Caleb at the University of Sydney, Australia, and her colleagues have spotted an extremely distant FRB that originated from a galaxy that existed just 3 billion years after the start of the universe, which is billions of years older than the previous record holder.

Caleb and her team first spotted the burst, called 20240304B, using the MeerKAT radio telescope in South Africa in March 2024 and followed up the source with observations from the James Webb Space Telescope. They found the flash came from a small, faint galaxy that appeared to be relatively young at the time the FRB was emitted and had formed its stars quickly.

“This is fantastically far away,” says Jason Hessels at the University of Amsterdam in the Netherlands. FRB 20240304B comes from a time in the universe called cosmic noon, when the rate of new stars forming was at its peak. This, along with the galaxy’s young age at that time, might suggest that this FRB, and at least some others, come from young stars that had only just exploded in supernovae and collapsed into magnetars, says Hessels.

One reason why astronomers are interested in FRBs is that the universe is full of ionised gas, which has lost its electrons due to radiation produced by stars. This gas makes up the vast majority of all matter in the universe, and understanding its distribution is key for working out how larger objects, like stars and galaxies, formed. But it is difficult to see unless there is a source of light passing through it, like an FRB.

“This bright flash is illuminating all of the ionised material between us and where the flash originated, so you can use that to map the gas, and magnetic fields, that are between stars and galaxies,” says Hessels.

Because FRB 20240304B was active during a time in the universe’s history when the first stars were forming and ionising the gas around them, we can use it to build a timeline of when those stars first switched on, says Anastasia Fialkov at the University of Cambridge. And this will only improve if we find even more distant FRBs.

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