Astronomers using South Africa’s MeerKAT radio telescope array have directly detected faint radio emissions from neutral hydrogen gas billions of light-years away, reaching Earth after a four- to-five-billion-year journey to offer a practical new tool for cosmological mapping.
Mapping the large-scale structure of the Universe efficiently requires tracing neutral hydrogen, one of the primary ingredients in how galaxies form and evolve. Yet that signal is notoriously faint and easily drowned out by foreground emission, human-made radio interference, and instrumental noise.
Conventional surveys tackled this by identifying and measuring individual galaxies one by one. But an international research team has sidestepped that restriction entirely, using radio observations alone to extract a collective hydrogen signal from two distinct epochs in cosmic history.
Extracting Faint Hydrogen Signals From Early MeerKAT Data
The breakthrough relies on hydrogen intensity mapping, a technique that measures the combined radio glow of many galaxies across vast cosmic volumes without needing to resolve them individually. 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, allowing astronomers to distinguish emissions from different chapters of cosmic history.
The international team, which included researchers from the University of Manchester and the University of the Western Cape, analyzed roughly 96 hours of observations recorded by South Africa’s MeerKAT radio telescope. The resulting measurements traced hydrogen across scales of several million light-years, which is roughly comparable to the distance separating the Milky Way and the neighboring Andromeda galaxy.
“This is a very exciting milestone. 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.”
Dr. Sourabh Paul, the study’s lead author, via Scitechdaily
A Rigorous Test Using Legacy Telescope Observations
Because those initial 2018 observations were not originally designed for hydrogen intensity mapping, the successful extraction serves as a powerful test of what scientists can salvage from archival telescope runs. It suggests a massive volume of untapped data sits waiting in telescope logs.
Photo: sciencedaily.com
“This was a challenging data analysis process, requiring a detailed understanding of the many sources of contamination that can affect such a faint measurement. 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.”
Professor Santos, via Scitechdaily
By combining the extracted signal’s position on the sky with the wavelength stretching caused by cosmic expansion, researchers can reconstruct a three-dimensional view of how matter is distributed across space. Previous reliable measurements at these distances typically forced astronomers to combine radio telescope data with separate optical galaxy surveys. The MeerKAT project achieved its detection using radio observations entirely on their own.
“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.”
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Dr. Zhaoting Chen, co-author of the study, via Scitechdaily
