MeerKAT Telescope Directly Detects Ancient Hydrogen Signal, Offering New Way to Map the Universe

Astronomers using the MeerKAT radio telescope in South Africa have directly detected the faint radio signal of hydrogen gas from 4 billion to 5 billion years ago, in research that could offer a new way to map the large-scale structure of the universe. The study, led by Sourabh Paul, was published in the July issue of The Astrophysical Journal Letters.

Neutral hydrogen, the universe's lightest and most abundant element, emits a faint radio signal known as the 21-centimeter line. As the cosmos expands, the wavelength of this signal stretches, or "redshifts," and the amount of stretching tells astronomers how long the signal has traveled and so how old the hydrogen is. Tracing this signal across the sky, a technique called hydrogen intensity mapping, lets astronomers build a 3D picture of the universe's largest structures without needing to detect every individual galaxy.

Until now, the technique had relied on combining radio detections with separate visible-light surveys of galaxies. The new study instead built a hydrogen intensity map using only radio data from MeerKAT, an array of 64 antennas in South Africa's Northern Cape, analyzing about 96 hours of observations that were originally collected in 2018, when the telescope had just begun science operations.

"This is a very exciting milestone," Paul said. "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."

The detected hydrogen spans distances of many million light-years, comparable to the distance between the Milky Way and the neighboring Andromeda galaxy. The team says future observations with MeerKAT, and eventually with the Square Kilometre Array Observatory under construction in Australia and South Africa, could extend the technique to cover larger areas of sky over longer periods.