Neutral hydrogen: MeerKAT detects the large-scale 21-cm signal at a significance of 6.2
· BehindLines newsroom
The MeerKLASS collaboration reports a direct measurement of the 21-cm radio signal from neutral hydrogen on large scales, made with South Africa's MeerKAT radio telescope. The technique, known as intensity mapping, aims to trace how matter is distributed across the Universe.
According to the accepted paper on arXiv (submitted October 8, 2026 and accepted by Monthly Notices of the Royal Astronomical Society), the team used 2021 data covering about 236 square degrees in the 971-1,024 MHz band, at redshift z = 0.42. The release carried by Phys.org on November 4 speaks of roughly 250 square degrees and a signal emitted about 4.5 billion years ago.
The challenge is considerable: according to Phys.org, foreground emission is about 10,000 times stronger than the signal being sought. MeerKAT's 64 dishes were used as independent telescopes rather than as a single interferometer. Mário Santos is principal investigator of the MeerKLASS survey at the University of the Western Cape. According to arXiv, the analysis covers scales from 0.095 to 0.245 h/Mpc and applies blind contaminant separation to each subset; the authors present it as a step toward HI intensity mapping with the SKA Observatory, for which MeerKAT is a precursor. The data are split into subsets, and cross-correlating them suppresses instrumental noise.
The result is a detection with a signal-to-noise ratio of 6.2, a little over six times the statistical noise. The clustering amplitude of the hydrogen is estimated at 10³ Ω_HI b_HI = 1.271, with a wide uncertainty (+1.080/−0.598). Mário Santos, quoted by Phys.org, calls it "a milestone" in establishing the technique as a cosmology tool.
What remains unknown: the authors acknowledge excess power in the individual subsets' spectra, which they attribute to unresolved systematics, and the measurement covers only one patch of sky and one epoch. The uncertainty on the amplitude remains large.