Scientists are turning to hydrogen, the most abundant element in the cosmos, to unravel the secrets of dark energy, the enigmatic force responsible for the accelerating expansion of the universe. This breakthrough stems from new findings that the Canadian Hydrogen Intensity Mapping Experiment (CHIME) can detect the faint radio signature of hydrogen from the distant past without relying on expensive cross-correlations with other telescopes.
CHIME was originally designed to investigate the pervasive influence of dark energy. Mark Halpern, the project’s principal investigator at the University of British Columbia, highlighted the significance of this achievement. “This is a completely new technique for probing the cosmos, delivered by an instrument that was conceived and built by Canadians,” Halpern said. “It’s a bold new step in the global cosmology program and a Canadian success story.”
Dark energy presents a unique challenge because it began influencing the fabric of space only after the initial expansion from the Big Bang had slowed. Researchers often compare this to a child on a swing that stops moving and then begins oscillating faster and faster without any external push. The implications of this accelerating expansion are profound: if dark energy continues to strengthen, it could lead to a “Big Rip” where space is torn apart, or alternatively, if it weakens, gravity could cause the universe to collapse back into a singularity in a “Big Crunch.” Currently, dark energy constitutes 68% of the universe’s matter-energy budget.
Arnab Chakraborty of the University of Toronto explained the role of hydrogen in this investigation. “Hydrogen is the most common element in the universe and the raw material from which stars form,” he said. “Its faint radio emission acts like a cosmic tracer, revealing how matter is distributed across space.”
Previously, mapping hydrogen distribution required correlating CHIME data with galaxy survey observations from other telescopes, a process costing millions of dollars and limited to star-dense regions. However, the team has now demonstrated they can map the radio glow independently. By analyzing just 94 nights of observation data from 2019, they detected a hydrogen signal dating back to when the universe was 5 billion years old.
Shabbir Shaikh from Arizona State University noted that the data indicates approximately 2% of hydrogen was in neutral atomic form at that time, consistent with previous measurements. “By measuring how that hydrogen is distributed and clustered, CHIME gives us a new way to test our understanding of how galaxies form and evolve,” Shaikh said.
With seven years of data now collected, researchers aim to probe hydrogen distribution further back to just 3 billion years after the Big Bang. The findings were published in two papers in The Astrophysical Journal.
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