Astronomers trace most distant fast radio burst to an early galaxy

Astronomers at the University of Sydney reported on October 8 that they had traced FRB 20240304B, a fast radio burst detected in South Africa, to a galaxy seen when the universe was about 3 billion years old. The result sets a distance record for a burst linked to its host galaxy and extends a method for studying matter between galaxies.

The flash travelled for more than 10 billion years before reaching Earth, according to the University of Sydney account. The team's study, reported as published in Science on October 8, places its source at a redshift of 2.148, plus or minus 0.001. Redshift measures how much the expansion of the universe has stretched light on its journey to Earth.

How astronomers traced FRB 20240304B

The MeerTRAP project detected the burst with South Africa's MeerKAT radio telescope. It was recorded in 2024; lead author Manisha Caleb told ABC that the final letter in its designation means it was the second fast radio burst discovered that day. Detecting a brief radio flash, however, did not by itself reveal the galaxy that produced it.

Caleb told ABC that the burst had a dispersion measure of about 2,400, which led the researchers to suspect a distant source. Dispersion describes how radio waves at different frequencies arrive at different times after passing through material in space. The team then used observations from NASA's James Webb Space Telescope to identify the host galaxy, according to the study abstract.

What the distance record allows researchers to test

The authors say the discovery doubles the redshift reach of localized fast radio bursts. A localized burst has a known host, giving astronomers both a distant endpoint and a radio signal altered by the material it crossed. That combination can help them examine matter spread through the universe across a longer stretch of cosmic history.

The study describes the signal as probing ionized baryons across about 80% of cosmic history. Baryons are the ordinary matter that makes up gas and stars; much of that material between galaxies is difficult to observe directly. Ryan Shannon, an astrophysicist interviewed by ABC, said distant bursts with identified hosts could help map matter distributed through the cosmic web.

This particular signal's path intersects the Virgo Cluster and a foreground group, the study reports. Its authors say the observations reveal complexity in magnetic fields across very large distances. Those intervening structures matter when interpreting what a burst's radio waves say about space between its source and Earth.

Does the host galaxy reveal what caused the burst?

The galaxy's vigorous star formation offers a clue, but the source of this burst has not been established. The University of Sydney account says its young, active character is more consistent with a possible young magnetar than with explanations involving mergers of older neutron stars. A magnetar is a neutron star with an unusually strong magnetic field.

Shannon told ABC that a magnetar in the Milky Way has produced a pulse resembling a fast radio burst, while cautioning that there may be more than one way to make these flashes. Fast radio bursts last only milliseconds, and their origins remain uncertain. This host-galaxy finding does not show that all such bursts share one mechanism.

The first fast radio burst was identified in archived data from Australia's Parkes telescope in 2007, ABC reports, and hundreds have since been found. Finding a host for a particularly distant event adds information that detection alone cannot provide. The University of Sydney account says researchers hope to push observations farther toward the era of the first generations of stars; whether more bursts can be localized at such distances remains an open question.