The radio flash traced to a dwarf galaxy in the young Universe

A radio signal lasted only milliseconds, yet it crossed billions of years of cosmic history before reaching Earth. The pulse FRB 20240304B was detected on March 4, 2024, by the MeerKAT radio telescope in South Africa. On October 8, 2026, researchers announced that observations from the James Webb Space Telescope had allowed them to identify its host galaxy and measure its distance.

Tracking such a brief pulse is not enough to find where it came from. The team used the signal’s precise position to search for a galaxy at the same location in the sky. Earlier ground-based observations found no visible host. Webb’s Near-Infrared Camera, or NIRCam, revealed a faint dwarf galaxy there. Its Near-Infrared Spectrograph, NIRSpec, measured the galaxy’s redshift at 2.148. That value means the light we see left the galaxy when the Universe was roughly 3 billion years old.

The host was unexpected: small, low in mass and actively forming stars. It is about a thousand times less massive than the team expected based on other galaxies associated with fast radio bursts. The result expands the range of environments known to host these events. It also shows how a burst can act as a beacon: on its journey to Earth, its signal carries information about the gas and cosmic structures along the way.

That information helps researchers test explanations for FRBs, short for fast radio bursts. One hypothesis involves magnetars — neutron stars with extraordinarily strong magnetic fields — which may form after the collapse and explosion of a massive star. Another proposes mergers between neutron stars, a process that can take much longer. The properties of this host galaxy are consistent with faster-origin scenarios, but they do not prove that a magnetar produced this burst. The origin of FRBs remains unresolved.

In plain language, this is not a photograph of the radio flash in action. It is the identification of a cosmic address associated with the event. Webb’s image shows the host galaxy and marks the FRB’s position with a white cross; the image was made from observations taken on December 26, 2024, almost ten months after the burst was detected. The study published in Science turns this tiny galaxy into a clue for investigating both possible FRB progenitors and the matter between galaxies.

Critical reading: The redshift of 2.148 places the galaxy in a very early era of the Universe. Comparing its mass with other known FRB hosts is informative, but the sample of localized FRBs at great distances remains small.