MeerKAT Telescope Directly Detects Faint Hydrogen Signal From Early Universe

Astronomers from the University of Manchester and the University of the Western Cape have directly detected an extremely faint radio signal from neutral hydrogen billions of light-years away, using South Africa's MeerKAT radio telescope. Published in The Astrophysical Journal Letters, the findings demonstrate a technique called hydrogen intensity mapping, which lets astronomers study huge regions of the cosmos more efficiently than before.

Neutral hydrogen naturally emits a faint radio signal called the 21-centimeter line. As the universe expands, this signal stretches to longer wavelengths, letting astronomers observe hydrogen from different eras of cosmic history. Rather than detecting galaxies one by one, hydrogen intensity mapping measures the combined radio emission from many unresolved galaxies, making it possible to study huge volumes of space and build a three-dimensional map. Until now, such detections typically combined radio and optical data; this study used MeerKAT observations alone.

The team analyzed around 96 hours of MeerKAT observations and detected the signal from two periods in cosmic history, corresponding to emissions that traveled roughly 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 Andromeda. "This is a very exciting milestone," said Dr. Sourabh Paul, the study's lead author, noting the signal is extremely faint and hard to isolate from foreground emission and interference. Professor Santos said the data, gathered in 2018 when MeerKAT had just begun operations, required understanding many sources of contamination.

Co-author Dr. Zhaoting Chen said neutral hydrogen is key to understanding how galaxies form and evolve, since intensity mapping measures a collective signal across large volumes without detecting every galaxy individually. The technique is expected to become a major science driver for the Square Kilometer Array Observatory (SKAO), for which MeerKAT is a precursor telescope. Professor Laura Wolz said future observations covering larger sky areas will map hydrogen in even greater detail.