Astronomers using South Africa's MeerKAT radio telescope have directly detected faint neutral hydrogen signals from 3.67 and 4.76 billion light-years away. The achievement, announced in a study published in The Astrophysical Journal Letters, marks a major milestone for hydrogen intensity mapping in cosmological research.
MeerKAT Captures Faint Signals from the Ancient Universe
An international team of researchers analyzed archival MeerKAT radio telescope observations to spot neutral hydrogen gas from roughly four and five billion years ago. The array, operated by the South African Radio Astronomy Observatory in the country's remote Karoo region, consists of 64 dish antennas located in South Africa's Northern Cape province. The team examined approximately 96 hours of data collected back in 2018 to isolate the subtle 21-centimeter emission lines.
Lead author Sourabh Paul, a Research Associate at the University of Manchester in Britain, noted the significance of the detection. The findings correspond to redshifts of approximately z = 0.32 and 0.44, revealing hydrogen that existed when the Universe was about 10 and 9 billion years old, respectively.
As Paul explained in a University of Manchester press release, 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.
Unlocking Universe Mapping via Hydrogen Intensity Techniques
Hydrogen Intensity Mapping (HIM) consists of detecting and measuring neutral hydrogen, which naturally emits a faint radio signal known as the 21-cm line. Hydrogen intensity mapping measures the combined emission from many unresolved galaxies rather than detecting individual galaxies, enabling surveys of vast regions of the universe. As the Universe expands, the wavelength of this signal is lengthened, thus allowing astronomers to study the Universe at different periods of cosmic history.
Previous robust detections of the signal at similar redshifts have typically combined radio observations with optical galaxy surveys. This latest study was the first time astronomers directly detected cosmic hydrogen using a single observatory, rather than combining radio and optical data from multiple observatories. The dataset examined by researchers was originally gathered nearly a decade ago when MeerKAT had just commenced science operations, suggesting there could be many more valuable signals in the observatory's archival data.
“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.”
Laura Wolz, co-author from the University of Manchester
Implications for Future Cosmology and the Square Kilometre Array
The successful extraction of early data opens new pathways for studying how galaxies form and evolve over cosmic time in a way that is much more efficient than individual studies. Researchers from multiple institutions contributed to the effort, including the Jodrell Bank Center for Astrophysics at the University of Manchester, the University of the Western Cape (UWC) in South Africa, the Royal Observatory's Institute for Astronomy at the University of Edinburgh, the South African Radio Astronomy Observatory (SARAO), and McGill University in Montreal. UWC spokesperson Gasant Abader spoke about the finding, noting that it marks a significant step toward using neutral hydrogen to map the three-dimensional structure of the universe on large scales.
Co-author Professor Laura Wolz from the Jodrell Bank Center for Astrophysics also emphasized that MeerKAT continues to open new windows for cosmology. As noted by the team, the process required accounting for the many sources of radio contamination that could obscure the faint signal.
These methodological refinements lay the groundwork for upcoming cosmological surveys, which will include HIM studies performed using the Square Kilometer Array Observatory (SKAO). This array will combine data from MeerKAT and the Inyarrimanha Ilgari Bundara — also known as the Murchison Radio-astronomy Observatory (MRAO) — in Western Australia, which is expected to gather its first light sometime next year ahead of science operations expected to begin around 2028.
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