MeerKAT’s direct detection of distant hydrogen emissions advances a way to map the universe without identifying galaxies individually.
Astronomers using South Africa’s MeerKAT radio telescope have directly detected faint radio emissions from neutral hydrogen gas billions of light-years away. The signal traveled for roughly four to five billion years before reaching Earth, offering a way to study the universe’s structure during an earlier chapter of its history.
The international team, including researchers from the University of Manchester and the University of the Western Cape, extracted the signal from about 96 hours of observations. They detected hydrogen emissions from two periods in cosmic history using radio observations alone. Reliable detections at these distances have typically required combining radio data with optical surveys of galaxies.
Mapping galaxies through their combined radio glow
Published in The Astrophysical Journal Letters, the findings advance a technique called hydrogen intensity mapping, which uses the collective radio emissions of many galaxies to map large volumes of space. It could help researchers investigate both the development of galaxies and the distribution of matter across the universe.
“Neutral hydrogen is one of the key ingredients for understanding how galaxies form and evolve,” said study co-author Dr. Zhaoting Chen.
“With intensity mapping, we do not need to detect every individual galaxy. Instead, we can measure the collective signal from hydrogen across large cosmic volumes, giving us a new way to study both galaxy evolution and the underlying matter distribution of the Universe.”
Neutral hydrogen naturally emits radio waves at a wavelength of about 21 centimeters, or 8.3 inches. As the universe expands, it stretches those waves to longer wavelengths. Measuring that stretching lets astronomers distinguish emissions from different stages of cosmic history.
Combining this information with the signal’s position on the sky makes it possible to build a three-dimensional picture of cosmic structure. Because intensity mapping collects emissions from galaxies that are not individually resolved, it offers an efficient way to survey enormous regions of the universe.
Extracting hydrogen’s signal from early MeerKAT data
The MeerKAT measurements trace hydrogen across scales of several million light-years, comparable to the distance between the Milky Way and its neighboring galaxy, Andromeda. Extracting that distant signal means separating it from other radio emissions and effects introduced by the telescope itself.
“This is a very exciting milestone,” said Dr. Sourabh Paul, the study’s lead author. “Hydrogen intensity mapping has long been seen as a promising way to map the Universe efficiently, but the signal is extremely faint and difficult to isolate from foreground emission, human-made radio-frequency interference, and instrumental effects. Detecting it directly with MeerKAT shows that this technique is becoming a practical tool for cosmology.”
The observations came from 2018, when MeerKAT had only just begun science operations. They were not originally designed for hydrogen intensity mapping, making the analysis a test of what researchers could recover from existing telescope data.
“This was a challenging data analysis process, requiring a detailed understanding of the many sources of contamination that can affect such a faint measurement,” said Professor Santos. “It is particularly remarkable that the data used in this study were taken in 2018, when MeerKAT had only just started science operations. There is now a rich trove of MeerKAT data waiting to be explored with this method.”
Toward more detailed cosmic hydrogen maps
The result also helps establish a path for future surveys with the Square Kilometre Array Observatory, or SKAO. MeerKAT is a precursor telescope for the observatory, where hydrogen intensity mapping is expected to become a major area of research.
“MeerKAT continues to open new windows for cosmology,” said Professor Laura Wolz, a study co-author from the University of Manchester. “The fact that this signal can be extracted from observations that were not originally designed for hydrogen intensity mapping is very encouraging. It shows the enormous scientific value of MeerKAT data and points the way to future observations with SKAO.”
The researchers say longer observations covering larger areas of the sky will allow more detailed hydrogen maps. Those measurements could help reveal how galaxies formed and evolved, how dark matter shapes the cosmic web, and how the universe has changed over billions of years.
Reference: “A Direct Detection of Neutral Hydrogen Intensity Mapping on Mpc Scales at z ≈ 0.32 and z ≈ 0.44” by Sourabh Paul, Zhaoting Chen, Mario G. Santos and Laura Wolz, 6 July 2026, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/ae808f
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