Ancient hydrogen has given scientists a fresh avenue to investigate the universe’s accelerating expansion, with a Canadian radio telescope demonstrating it can chart this elusive signal using only its own measurements.
A set of instruments known as the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, has for the first time shown it can map the distribution of ancient hydrogen gas without relying on outside observatories, according to a study published Monday, Sept. 28, in The Astrophysical Journal. Researchers said the result, seven years in the making, could open a cost-effective path to probing dark energy, the mysterious driver of cosmic acceleration.
Ancient hydrogen as a cosmic tracer
Hydrogen is the most abundant element and the basic fuel for star formation. Its faint radio emission allows astronomers to trace how matter is spread through space. “Its faint radio emission acts like a cosmic tracer, revealing how matter is distributed across space,” said study co-author Arnab Chakraborty, a postdoctoral fellow at the University of Toronto, in a statement.
CHIME, a set of stationary radio telescopes near Penticton, British Columbia, scans the entire northern sky daily. Until now, the instrument’s detections needed confirmation from other facilities, a process that added time and cost. The team said establishing CHIME as an independent measurement was essential to provide a standalone benchmark for studies of the early universe.
Seven years to validate the signal
The new paper draws on 94 nights of observations collected in 2019, which the team extensively vetted before release. CHIME can detect signals from as early as about 3 billion years after the Big Bang. “We worked very hard to convince ourselves that this wasn’t a false alarm,” Chakraborty said. “After all the tests, the signal remained. That gave us confidence we were seeing real hydrogen from the distant universe.”
Companion analysis refines hydrogen’s state
An accompanying study in The Astrophysical Journal provides additional detail on where hydrogen resides in the cosmos. That analysis indicates roughly 2% of hydrogen is neutrally atomic, meaning each atom has one proton and one electron and no net electric charge. Co-author Shabbir Shaikh, a postdoctoral fellow in the School of Earth and Space Exploration at Arizona State University, said the estimate is broadly consistent with results from other instruments.
Implications for dark energy and future work
Charting the distribution of ancient hydrogen across cosmic time can help researchers track how the universe expanded at different epochs, which in turn informs models of dark energy. The team plans to analyze CHIME’s remaining seven years of observations to strengthen these measurements and improve maps of hydrogen gas in the distant universe, complementing findings from missions such as Artemis II.