Webb Traces 10-Billion-Year-Old Deep Space Signal To Its Source

Astronomers using the James Webb Space Telescope (with initial data captured by South Africa's MeerKAT radio telescope) have localized the most distant fast radio burst ever recorded: a signal that traveled across space for more than 10 billion years before reaching us.

The powerful, millisecond-long pulse of radio waves (designated FRB 20240304B) originated when the universe was only about three billion years old and has traveled through roughly 80% of cosmic history, which is double the distance record of any previously identified fast radio burst.

When the MeerTRAP team detected the signal using MeerKAT in 2024, initial radio data hinted that the burst had traveled across vast cosmological distances, although ground-based observatories failed to detect any galaxy at the precise point in the sky where the signal originated. Scientists then pointed Webb's NIRCam and NIRSpec at the target area and were able to pinpoint a faint host galaxy with a redshift of 2.148.

Here's the thing: most FRBs identified to date reside within massive, metal-rich, mature star-forming galaxies. By contrast, the host galaxy of FRB 20240304B turned out to be a dwarf galaxy roughly 1,000 times less massive than anticipated, characterized by a low concentration of metals and an intense burst of rapid star formation.

Nonetheless, this environment could offer clues about what actually generates fast radio bursts. One leading hypothesis suggests that FRBs stem from the collision and merger of two binary neutron stars. However, orbital decay between neutron stars takes billions of years, making mergers unlikely to occur within such young, pristine dwarf systems.

Instead, another theory favors an origin involving a single, young magnetar, i.e. a highly magnetized neutron star created in the immediate aftermath of a giant star's supernova. In a rapidly star-forming, metal-poor dwarf galaxy, massive stars die quickly and yield magnetars almost immediately, producing high-energy bursts like FRB 20240304B without a long delay.

As radio waves travel billions of light-years across space, they pass through diffuse intergalactic gas, dust, and cosmic structures. The particles along the signal's path slightly slow down different radio frequencies, leaving a distinct imprint that allows astronomers to measure the unseen matter filling the cosmic web. Upon analyzing the signal's dispersion, researchers found the imprint of two intervening cosmic structures: a previously unknown galaxy cluster roughly 3.5 billion light-years away, and the nearby Virgo Cluster located 54 million light-years away.