The breakthrough could give scientists a faster and less expensive way to study dark energy, the mysterious phenomenon believed to be accelerating the expansion of the universe. Understanding dark energy remains one of the biggest unsolved problems in modern physics.

The results, published in The Astrophysical Journal, also mark an important milestone for CHIME, which was originally designed to make this type of measurement.

“Hydrogen is the most common element in the universe and is the raw material from which stars are formed,” said co-author Dr. Arnab Chakraborty, a postdoctoral fellow at the University of Toronto who first proposed the discovery. “Its weak radio emissions act like cosmic trackers, revealing how matter is distributed in space.”

Scientists have proposed competing explanations for the nature of dark energy. Because CHIME can make these measurements using its own data, researchers can independently test those ideas and gather evidence that may support or challenge existing theories.

“This is a completely new technology for exploring space, made possible by an instrument designed, built and funded by Canadians,” said co-author Dr. Mark Halpern, professor in UBC’s Department of Physics and Astronomy and CHIME principal investigator. “This is a bold new step in the global cosmology program and a Canadian success story.”

How CHIME Maps the Universe with Hydrogen

CHIME is a radio telescope located near Penticton, British Columbia, and hosted by the National Research Council of Canada (NRC). The instrument observes the entire northern sky every day.

The project brings together researchers from across Canada, including scientists from the University of British Columbia, McGill University, the University of Toronto and the Dominion Radio Astrophysical Observatory (NRC). Other North American collaborators are also joining the effort, including Arizona State University.

One of CHIME’s main goals is to chart how hydrogen gas was distributed in the early universe. By measuring its large-scale structure, astronomers can reconstruct how the universe expanded over time and use those measurements to investigate dark energy.

Until now, CHIME researchers had to compare radio observations with galaxy survey data collected by other telescopes. These studies address similar cosmological questions by examining light from galaxies, but they can cost millions of dollars and primarily probe regions of space that are hot and dense enough for stars to form.

CHIME instead measures the combined radio emissions produced by hydrogen itself. This approach allows researchers to explore much larger areas of the universe, reach farther into the past and pursue similar questions at a fraction of the cost, without relying on data from other surveys.

What the Hydrogen Signal Reveals

In an accompanying paper, the researchers analyzed what the newly detected signal could reveal about the distribution of hydrogen throughout the universe.

“Our data show that about 2 percent of the hydrogen in the universe was in the form of neutral atoms at this time, which is broadly consistent with other measurements,” said co-author Dr. Shabar Shaikh, a postdoctoral fellow at Arizona State University. “By measuring how hydrogen is distributed and clustered, CHIME provides a new way to test our understanding of how galaxies form and evolve.”

The measurement offers more than a new way to study the expansion of the universe. It will also help researchers test models of galaxy formation and better understand how matter is organized across the cosmos.

How Researchers Found Hydrogen Hidden in Cosmic Noise

The discovery was not a sudden breakthrough. Researchers developed new data-processing and analysis methods to extract the extremely weak hydrogen signal from much stronger interference.

The background included radio noise from space, signals produced by human technology and effects generated by the telescopes themselves. After identifying possible traces of hydrogen, the team spent more than a year testing the results to confirm that the signal was real.

The analysis ultimately showed that the signal came from hydrogen in distant space, about 5 billion years after the universe was created. The findings are based on 94 nights of observations collected in 2019.

“We tried very hard to convince ourselves that this was not a false alarm,” Dr. Chakraborty said. “After all the tests, the signal remained. This gave us confidence that we were seeing real hydrogen from distant space.”

Seven More Years of CHIME Data Could Reveal More

The new results represent only a small portion of the information CHIME has collected since it began operating.

Researchers currently have about seven years of observations available for analysis. They are working to extend the technique farther into the history of the universe, with the goal of studying a time when the universe was just 3 billion years old.

“Astrophysicists have long believed that this hydrogen mapping technique using these types of telescopes has great potential. By actually showing that this technique works, we have opened a whole new window into the universe that we can use to test current theories and learn new things about galaxies and other properties of the universe,” said co-author Dr. Simon Foreman, assistant professor at Arizona State University.

This project is funded by the Canadian Foundation for Innovation. It includes the National Research Council of Canada, the Natural Sciences and Engineering Research Council, the provinces of British Columbia, Ontario and Quebec, and is supported by the Canadian Digital Research Alliance.