CHIME Telescope Makes First Solo Detection of Hydrogen Glow

The Canadian Hydrogen Intensity Mapping Experiment, known as the CHIME telescope, has made its first standalone detection of the faint radio glow of hydrogen gas from a time when the universe was about five billion years old. Researchers from India were part of the international collaboration behind the result, which opens a new route for studying cosmic expansion and dark energy.

The Indian link

The study included CHIME collaborators at the Raman Research Institute (RRI), an autonomous institute of the Department of Science and Technology. Saurabh Singh, associate professor at RRI and a co-author, described CHIME as an instrument that scans a large fraction of the cosmos as the sky drifts over it, with no moving parts, delivering a daily snapshot of the radio sky.

What is new about it

CHIME is an interferometric radio telescope in Canada, built to map how hydrogen gas is spread through the early universe so that astronomers can measure the universe's expansion and probe dark energy. Until now it had to cross-correlate its observations with galaxy survey data from other telescopes. This time it found the signal using only its own data. Because galaxy surveys cost far more and look only at the parts of the universe hot and dense enough to form stars, the standalone method promises a faster and cheaper way to study dark energy, which is one of the largest open questions in physics.

What the signal shows

An accompanying paper examined what the observed signal says about how hydrogen is spread through the universe. Shabbir Shaikh of Arizona State University, a co-author, said the data indicate that roughly two per cent of the universe's hydrogen was in neutral atomic form at that time, broadly in line with other measurements. Hydrogen, the most common element in the universe and the raw material of stars, acts as a cosmic tracer through its faint radio emission.

How the result was reached

This was not a sudden discovery. New data analysis and processing techniques were applied to pull the faint signal out of the noise of the background universe, of human technology and of the instrument itself, and the team then spent more than a year testing the finding. The measurement rests on 94 nights of observation data collected in 2019, a small fraction of what CHIME has gathered. The findings are published in The Astrophysical Journal. Researchers now have nearly seven years of observations and are extending the analysis to when the universe was only about three billion years old.