A radio flash lasting a few thousandths of a second has been traced back to a time roughly 3 billion years after the Big Bang, and the galaxy that hosted it is far smaller than anyone predicted. NASA’s James Webb Space Telescope pinned the source of FRB 20240304B to a dwarf galaxy at redshift 2.148, the most distant fast radio burst localized to date.
The host is the surprise. NASA’s release says the galaxy is 1,000 times less massive than the team expected, a result that complicates the standard picture of where these bursts come from and what makes them.
MeerKAT’s catch and Webb’s follow-up
The burst was detected on March 4, 2024, by the MeerTRAP team using South Africa’s MeerKAT radio telescope, according to NASA’s Webb mission team. The radio signal alone hinted that the source was extraordinarily far away, but the world’s largest ground-based telescopes could not see any galaxy at the burst’s position. That left the burst without a confirmed home, and without a home there was no reliable way to measure how far the signal had traveled or what kind of environment had produced it, so the team turned to Webb.
Webb closed the gap in two steps. Its Near-Infrared Camera detected the faint host galaxy, and its Near-Infrared Spectrograph measured the redshift at 2.148, which places the burst about 3 billion years after the Big Bang. NASA notes that most fast radio bursts detected so far went off billions of years later in cosmic history.
The finding is described in a paper in the journal Science led by Manisha Caleb of the University of Sydney. An earlier preprint posted to arXiv, headed “A fast radio burst from the first 3 billion years of the Universe,” gives the redshift as 2.148 plus or minus 0.001. Its authors say the localization doubles the redshift reach of pinpointed bursts and lets the signal probe ionized matter across roughly 80 percent of cosmic history.
A dwarf galaxy 1,000 times less massive than expected
Fast radio bursts were first discovered in 2007, and most are seen only once, which makes locating their homes difficult. The galaxies that have been identified are typically massive and still forming stars. A 2021 Hubble survey described on NASA’s Hubble pages placed five of eight localized bursts on or near the spiral arms of hosts that were mostly relatively young, star-forming and, in many cases, about as massive as the Milky Way.
FRB 20240304B does not fit that template. Caleb said in the NASA release that the team had pictured a big, nicely formed galaxy with lots of stars. What Webb showed instead was a small, actively star-forming dwarf galaxy that NASA describes as 1,000 times less massive than the team expected.
The galaxy existed during cosmic noon, the period of peak star formation in the universe, and its star-formation rate suggests most of its stars may have formed within about 30 million years. Co-author Ben Stappers of the University of Manchester said the host stands out from the entire sample of burst galaxies the collaboration has assembled, a sample that otherwise leans toward large, well-developed star-forming galaxies.
Joeri van Leeuwen of the Netherlands institute ASTRON, who was not involved in the work, told Sky & Telescope that the host galaxy is “unexpectedly small and has a very low luminosity.” Keck and MMT, two ground-based observatories, found no host candidate at the position before Webb looked.
Magnetar or merger: what the young host favors
Nobody knows what generates fast radio bursts, a point Caleb made directly in the release: the mystery of their origin is what makes them interesting. The new host narrows the field. A merger of two neutron stars takes billions of years to come about, so it would tie bursts to older galaxies. NASA says the authors consider that very unlikely for this burst, given that the host was already forming stars only about 3 billion years after the Big Bang.
The alternative is a young magnetar, a neutron star with strong, twisted magnetic field lines, left behind by a supernova. Such an object could produce a burst soon after its birth, through a process similar to starquakes, which fits a galaxy whose stars formed recently. The release presents this as a better fit for the evidence rather than a proven origin, and the authors stop short of naming a confirmed source.
The burst also served as a probe on its way to Earth. Its signal carries imprints of a previously unknown galaxy cluster at redshift 0.3, about 3.5 billion light-years away, and of the nearby Virgo Cluster, about 54 million light-years away. J. Xavier Prochaska of UC Santa Cruz, a co-author, compared a burst to “a cosmic flashlight” that “lights up everything along the path.”
The team estimates MeerKAT may detect and localize several bursts per year at redshift greater than 1.0, and Webb will be needed to characterize their hosts. If those hosts also turn out to be dwarf galaxies, FRB 20240304B stops being an outlier and becomes a population.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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