Astronomers from the University of Manchester and the University of the Western Cape have directly detected an extremely faint radio signal from hydrogen gas billions of light-years away, opening a powerful new way to map the large-scale structure of the universe. Using South Africa’s MeerKAT radio telescope, the international team measured radio emissions from neutral hydrogen dating back to a time when the universe was several billion years younger than it is today.
The findings, published in The Astrophysical Journal Letters, demonstrate the potential of a technique known as hydrogen intensity mapping, which allows astronomers to study vast regions of the cosmos more efficiently than ever before.
How hydrogen intensity mapping works
Neutral hydrogen naturally emits a faint radio signal known as the 21-centimeter line. As the universe expands, this signal is stretched to longer wavelengths, allowing astronomers to observe hydrogen at different stages of cosmic history.
Rather than detecting individual galaxies one by one, hydrogen intensity mapping measures the combined radio emission from many unresolved galaxies. This makes it possible to study enormous volumes of the universe and build a three-dimensional picture of its structure.
Until now, reliable detections of this signal at these distances have typically relied on combining radio observations with optical galaxy surveys. In this new study, however, the team directly detected the hydrogen intensity mapping signal using MeerKAT radio observations alone.
The team analyzed around 96 hours of observations from MeerKAT and detected the signal from two periods in cosmic history, corresponding to emissions that traveled for approximately four to five billion years before reaching Earth. The measurements trace hydrogen across scales of several million light-years—comparable to the distance between the Milky Way and its neighboring galaxy, Andromeda.
What the researchers say
“This is a very exciting milestone,” said Dr. Sourabh Paul, lead author of the study. “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.”
“This was a challenging data analysis process, requiring a detailed understanding of the many sources of contamination that can affect such a faint measurement,” Professor Santos added. “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.”
The researchers say the work opens new opportunities to measure neutral hydrogen over cosmological distances and study how galaxies form and evolve over cosmic time.
Dr. Zhaoting Chen, co-author of the study, said, “Neutral hydrogen is one of the key ingredients for understanding how galaxies form and evolve.
“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.”
The detection also has important implications for future cosmological surveys. Hydrogen intensity mapping is expected to become a major science driver for the Square Kilometer Array Observatory, for which MeerKAT is a precursor telescope.
Professor Laura Wolz, co-author of the study from the University of Manchester, added, “MeerKAT continues to open new windows for cosmology. 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 future observations covering larger areas of the sky and using longer observing times will enable astronomers to map hydrogen in even greater detail, helping reveal how galaxies formed, how dark matter shapes the cosmic web, and how the universe has evolved over billions of years.
Publication details
Sourabh Paul et al, A Direct Detection of Neutral Hydrogen Intensity Mapping on Mpc Scales at z ≈ 0.32 and z ≈ 0.44, The Astrophysical Journal Letters (2026). DOI: 10.3847/2041-8213/ae808f
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MeerKAT directly detects faint hydrogen signal from the distant universe (2026, September 1)
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