An international research team led by scientists at the University of Manchester and the University of the Western Cape has successfully detected a distant hydrogen signal using radio telescope observations, marking a significant advancement in cosmological mapping techniques. The findings, published in The Astrophysical Journal Letters, demonstrate the viability of hydrogen intensity mapping as a practical tool for surveying large regions of space. The researchers identified emissions from neutral hydrogen dating to a period when the Universe was billions of years younger than today, with the signal having traveled approximately four to five billion years before reaching Earth.
The hydrogen intensity mapping technique operates differently from traditional galaxy surveys by detecting the combined radio emissions produced by hydrogen across numerous galaxies rather than attempting to identify individual galaxies one at a time. Neutral hydrogen naturally emits a weak radio signal known as the 21-centimeter line, which becomes stretched to longer wavelengths as it travels through the expanding Universe. By measuring this wavelength shift, astronomers can study hydrogen from different periods in cosmic history. The researchers extracted this extraordinarily faint signal from approximately 96 hours of MeerKAT observations, allowing them to trace hydrogen across distances of several million light-years.
Previously, reliable measurements of hydrogen at such distances typically required astronomers to combine radio telescope data with optical galaxy survey information. The current study represents a milestone by directly identifying the hydrogen intensity mapping signal using MeerKAT radio observations independently. The data analysis process proved challenging, requiring researchers to carefully account for numerous sources of interference, including foreground emission, human-made radio-frequency interference, and instrumental effects that could distort measurements.
The successful detection opens new opportunities for investigating galaxy formation and evolution throughout cosmic history. The results are particularly significant given their implications for upcoming major cosmological surveys, as hydrogen intensity mapping is expected to become a primary scientific focus for the Square Kilometre Array Observatory, for which MeerKAT serves as a precursor facility. Future observations covering larger sky areas over extended periods should enable even more precise mapping of neutral hydrogen distribution and provide deeper insights into dark matter’s influence on cosmic structure.
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