Fast radio bursts have served astrophysicists as cosmic probes for about two decades: their dispersion measure (the signal delay in plasma) allows weighing the distribution of ionized matter along the line of sight. The Macquart relation links this measure to redshift and provides an independent way to estimate the Hubble constant and the baryon content. However, until now almost all localized FRBs were at redshifts below 0.5, and the region z > 1 remained unexplored due to limited telescope sensitivity and difficulties in obtaining spectra of distant galaxies. The discovery of FRB 20240304B at z=2.148 fills this gap and for the first time extends the method into the era of cosmic noon, the peak of star formation about ten billion years ago. The work stands alongside studies that use FRBs to probe magnetic fields, the cosmic web, and the Hubble tension, but it takes a decisive step into the high-redshift regime.
FRB 20240304B was detected on 4 March 2024 by the MeerTRAP system at the MeerKAT radio telescope in South Africa, in the 856–1712 MHz band. The dispersion measure, after correcting for scattering, was 2458.20 ± 0.01 pc/cm³. Localization with an accuracy of about 0.3 arcseconds was achieved using interferometric data with the VLASS catalog for astrometric calibration. Ground-based observations with the Keck and MMT telescopes did not reveal a host galaxy down to limiting magnitudes of R=26.24 and J=23.38, indicating a large distance. Then observations were carried out with the James Webb Space Telescope: the NIRCam camera in the F200W and F322W2 filters detected a faint galaxy at 0.3 arcseconds from the burst position, and the NIRSpec spectrograph in integral field mode measured Hα and [OIII] emission lines, yielding a spectroscopic redshift of z=2.148 ± 0.001. The probability of association between the burst and this galaxy, according to the Bayesian PATH method, was 97.5%.
FRB 20240304B turned out to be the most distant of all localized fast radio bursts: its redshift of 2.148 corresponds to a luminosity distance of 17.4 Gpc and a universe age of about 3 billion years. The burst energy in the rest frame was approximately $10^{41}$ erg, which is at the upper end of the typical range for FRBs. The host galaxy is a dwarf system with a stellar mass of about $10^7$ solar masses, a star formation rate of ~0.2 solar masses per year, and a metallicity of 10–20% solar. Its specific star formation rate places it above the main sequence, indicating a starburst and a young age: the time to form the entire stellar mass is estimated at 52 million years. The burst is strongly linearly polarized (49%) with a rotation measure of −55.6 ± 0.5 rad/m². Given the small contribution from the Milky Way and nearby sources, this means that the observed rotation measure is mostly intrinsic, and in the rest frame it increases to ~−550 rad/m². The excess dispersion measure over the median value for this redshift is about 550 pc/cm³; it is explained by the line of sight crossing the Virgo cluster (contribution ~235 pc/cm³) and a galaxy group at z=0.311 (~33 pc/cm³).
This discovery doubles the redshift range of localized FRBs and for the first time demonstrates that such bursts are born in the era of cosmic noon. Unlike neighboring works that studied FRBs at low and moderate redshifts or used statistical estimates, here direct spectroscopic confirmation for z>2 is obtained for the first time. The properties of the host galaxy, its low mass, active star formation, and low metallicity, indicate a short delay between the starburst and the appearance of the FRB, consistent with models of young magnetars. This rules out scenarios with long delays, such as neutron star mergers, for most FRBs. Furthermore, the work shows that FRBs can be used for tomography of the cosmic web and measuring magnetic fields on gigaparsec scales.
With the commissioning of more sensitive interferometers such as SKA-Mid, and the combined use of space telescopes for host identification, a sharp increase in the number of FRBs at z>2 is expected. This will allow building a statistically significant sample to test the Macquart relation in the distant universe, refine the Hubble constant, and probe the epoch of reionization. It will also become possible to study the evolution of magnetic fields in the intergalactic medium and in galaxy halos at high redshifts.
The result affects cosmology (independent measurement of baryon distribution and the Hubble constant), galaxy astrophysics (star formation in dwarf systems), and neutron star physics (the nature of FRB sources).
A systematic search for FRBs at z>2 is needed using MeerKAT and future instruments, as well as detailed modeling of the contribution of clusters and groups of galaxies to the dispersion measure along the line of sight.
For radio astronomy, the key unresolved problem is the nature of FRB sources and their connection to the neutron star population. The discovery of an FRB at z=2.148 in a dwarf galaxy with active star formation supports the magnetar origin and short delay, but the question remains whether all FRBs are born in such environments. Another problem is the precise measurement of the contribution of various components (intergalactic medium, galaxy halos, clusters) to the dispersion measure, which is critical for cosmological applications.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The paper reports the discovery of FRB 20240304B at a redshift of 2.148, making it the most distant localized fast radio burst. The burst was detected by the MeerKAT telescope, localized to 0.3 arcseconds, and its host galaxy was identified with JWST as a dwarf system with active star formation. The authors measured the dispersion measure, estimated the energy, and characterized the host, linking the burst to the epoch of cosmic noon.
Where its strength is
This work is the first to extend the FRB dispersion measure method to redshifts z > 2, where no localized bursts were previously available. It opens the possibility of directly probing ionized baryons during the peak epoch of star formation and galaxy assembly.
Where it could go next
Worth trying
Why this may matter
Extending the redshift range of localized FRBs to z=2.148 makes them a full-fledged tool for cosmology and high-redshift astrophysics. This could help resolve the Hubble tension, refine the baryon budget at cosmic noon, and trace the evolution of magnetic fields in the Universe.
Nearby works in our archive
The closest work in the archive sits at 0.65 by meaning — the usual level for our corpus.
The light from FRB 20240304B traveled to Earth for 10.5 billion years, about three-quarters of the age of the universe. During that time, galaxies, stars, and planets formed on Earth, and radio telescopes appeared that caught this millisecond pulse.