MeerKAT Detects Ancient Hydrogen Signal to Map Universe

MeerKAT alone detected faint neutral hydrogen emission from 4–5 billion years ago, opening a new path to mapping the cosmos.

An international team led by the University of Manchester and the University of the Western Cape used South Africa's MeerKAT radio telescope to detect an exceptionally faint radio signal from neutral hydrogen gas billions of light-years away. The emissions date to a period when the Universe was several billion years younger than it is today, and had traveled roughly four to five billion years before reaching Earth. The findings were published in The Astrophysical Journal Letters.

Until now, reliable measurements of hydrogen at such distances generally required combining radio observations with data from optical galaxy surveys. This study detected the hydrogen intensity mapping signal using MeerKAT radio data alone. ScienceDaily notes the signal is extremely faint and difficult to isolate from foreground emission, human-made radio-frequency interference, and instrumental effects, making a direct detection a notable technical milestone. The Business Standard reports the data were collected in 2018, when MeerKAT had only recently begun science operations, so the achievement came from data never originally designed for this purpose.

The researchers analyzed about 96 hours of MeerKAT observations and found the signal from two separate periods in cosmic history, at redshifts the paper identifies as approximately z ≈ 0.32 and z ≈ 0.44. The observations allowed the team to trace hydrogen across distances of several million light-years, a scale ScienceDaily compares to the separation between the Milky Way and the Andromeda galaxy. todaypress.tv reports the MeerKAT array consists of 64 antennas, and that the method measures cumulative hydrogen emission rather than detecting each galaxy individually.

Neutral hydrogen is a key ingredient for understanding how galaxies form and evolve, and intensity mapping offers a way to study vast cosmic volumes efficiently without cataloging individual galaxies. Lead researcher Dr. Sourabh Paul said the direct detection shows the technique is becoming a practical tool for cosmology, according to ScienceDaily. Co-author Dr. Zhaoting Chen told the outlets that measuring the collective hydrogen signal across large regions provides a new way to investigate both galaxy evolution and the underlying matter distribution of the Universe.

MeerKAT serves as a precursor to the Square Kilometre Array Observatory (SKAO), and hydrogen intensity mapping is expected to be a major scientific focus for that facility. According to The Business Standard, Professor Laura Wolz said extracting the signal from observations not originally designed for the technique highlights the scientific value of MeerKAT data and points the way to future SKAO observations. The team plans to process more extensive and longer observations covering larger portions of the sky to build more precise hydrogen maps, study dark matter's influence on the cosmic web, and reconstruct how the Universe has changed over billions of years.