Astronomers utilizing the MeerKAT radio telescope have successfully detected signals from neutral hydrogen gas located billions of light-years away, offering a promising new method for charting the large-scale structure of the universe.
The research, published in the July edition of The Astrophysical Journal Letters, marks a significant milestone for hydrogen intensity mapping. This technique involves tracing the locations of hydrogen, the cosmos’s most abundant element, to build three-dimensional maps of vast cosmic structures. Neutral hydrogen emits a faint radio signal known as the 21-centimeter line. As the universe expands under the influence of dark energy, this signal is stretched or redshifted, allowing astronomers to determine the distance and era from which the emission originated.
Previously, hydrogen intensity mapping required combining radio wave detections with observations from visible-light galactic surveys. However, this latest study breaks from that convention by constructing a hydrogen map using only radio waves collected by MeerKAT, an array of 64 antennas situated in the Northern Cape of South Africa.
“This is a very exciting milestone,” said team leader Sourabh Paul. “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.” He added that detecting the signal directly with MeerKAT demonstrates that the technique is becoming a practical tool for cosmology.
The research team analyzed approximately 96 hours of observations from 2018, when MeerKAT had just begun its science operations. They identified hydrogen signals dating back 4 billion to 5 billion years, spanning distances comparable to the gap between the Milky Way and the Andromeda galaxy.
Zhaoting Chen of the University of Edinburgh highlighted the efficiency of the method. “Neutral hydrogen is one of the key ingredients for understanding how galaxies form and evolve,” Chen stated. “With intensity mapping, we do not need to detect every individual galaxy. 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.”
Laura Wolz of the University of Manchester noted that the ability to extract these signals from data not originally designed for this purpose is encouraging. She emphasized the technique’s importance for future surveys, including those by the Square Kilometre Array Observatory (SKAO), which is currently under construction in Western Australia and South Africa.
Mario G. Santos of the University of the Western Cape described the data analysis as a challenging process requiring a deep understanding of contamination sources. He expressed optimism about the potential of the extensive MeerKAT archive. “There is now a rich trove of MeerKAT data waiting to be explored with this method,” Santos said.
The team plans to collect further observations covering larger sky areas over extended periods. These efforts aim to produce more detailed hydrogen maps, ultimately helping scientists understand how the universe’s largest structures have evolved over billions of years.
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