An international team of astronomers has used South Africa’s MeerKAT radio telescope to directly detect faint radio emissions from neutral hydrogen gas across cosmic distances. Published in The Astrophysical Journal Letters, the research provides a new way to map the large-scale structure of the universe without needing to combine radio observations with optical galaxy surveys.
Astronomers Detect Faint Hydrogen Signal Using MeerKAT Telescope
The study was conducted by researchers from the University of the Western Cape (UWC) in South Africa and Britain’s University of Manchester. The project was initiated in 2021 at UWC while lead author Sourabh Paul worked as a postdoctoral researcher in the research group of Professor Mario Santos.
The team analyzed approximately 96 hours of MeerKAT observations and detected the signal from two distinct periods in cosmic history, corresponding to redshifts of roughly 0.32 and 0.44. These emissions traveled between four and five billion years before reaching Earth, tracing hydrogen across megaparsec scales comparable to the distance between the Milky Way and its neighboring galaxy, Andromeda.
Neutral hydrogen naturally emits a faint radio signal known as the 21-cm line. As the universe expands, this signal is stretched to longer wavelengths, allowing scientists to trace hydrogen across different stages of cosmic history. Rather than detecting individual galaxies one by one, the method of hydrogen intensity mapping measures the combined emission from many unresolved galaxies.
The signal is extremely faint and difficult to isolate from foreground emission, human-made radio-frequency interference, and instrumental effects,
Sourabh Paul said in a News. Detecting it directly with MeerKAT shows that this technique is becoming a practical tool for cosmology.
Overcoming Data Challenges and Early Observations
Extracting the delicate hydrogen line presented significant data analysis hurdles due to various sources of contamination. Researchers noted that the dataset utilized in the study was originally gathered in 2018 when the instrument had only just started science operations.
It is particularly remarkable that the data used in this study were obtained in 2018, before MeerKAT had started science operations,
said Dr. Fernando Camilo, chief scientist at the South African Radio Astronomy Observatory (SARAO), which built and operates the 64-dish telescope in the remote Karoo region of the Northern Cape. We obtained these data to demonstrate the technical readiness of the telescope, not with any particular scientific goal in mind.
Co-author Zhaoting Chen noted that neutral hydrogen serves as a key ingredient for understanding galaxy formation and evolution. With intensity mapping, we do not need to detect every individual galaxy,
Chen said. 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.
Implications for Future Telescopes
The success of these observations points toward future cosmological surveys. MeerKAT serves as a precursor telescope to the Square Kilometer Array Observatory, which is expected to begin science operations around 2028, and the international SKA-Mid telescope currently under construction in South Africa.
MeerKAT continues to open new windows for cosmology,
said Laura Wolz, a 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.
