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Mark Halpern, a professor at the University of British Columbia who is a principal investigator with the team that conducts work with the CHIME radio telescope in Penticton B.C., in 2017.Ivan Semeniuk/The Globe and Mail
Hydrogen is both the simplest atom in nature and the most abundant. It is the fuel that allows stars to shine and, in doing so, makes life possible.
Now astronomers working with a unique radio telescope in British Columbia have achieved the most distant measurement to date that shows how hydrogen atoms are distributed in the deep universe.
The result supports an emerging picture of how matter organized itself after the Big Bang and built the universe we know today.
“What we really are tracing are huge clusters and families of galaxies and the filaments that make up the dense structure of space,” said Mark Halpern, a professor at the University of British Columbia who is a principal investigator with the team that conducted the work.
He said that as he and his colleagues work to better understand the signal, it may allow for something more ambitious: a direct measurement of the rate at which the universe is expanding. This would provide an independent way to gauge the influence of dark energy, an unknown phenomenon that is thought to be causing the expansion to speed up.
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The detection was made using the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, based in Penticton, B.C.
It consists of a series of trough-like antennas which passively gather radio waves from the heavens. As the Earth turns, the antennas sweep across the northern sky, gradually collecting data from a vast volume of space. The heart of the instrument is a sophisticated computer system that disentangles all the information coming from many directions and turns it into a coherent picture of the radio sky.
Since it was first switched on in 2017, CHIME has routinely detected a wide range of radio sources such as pulsars (rapidly spinning stellar corpses scattered throughout our Milky Way galaxy) and fast radio bursts (brief but intense blasts of radio energy coming from sources inside galaxies far beyond our own).
But CHIME’s original purpose was to detect the much quieter and diffuse radio emission produced by hydrogen atoms in the cold depths between galaxies. Nine years after its work began, the project appears to have realized this goal.
In a pair of studies published Monday in the Astrophysical Journal, astronomers revealed their detection of a hydrogen signal at approximately 8 billion light years from Earth, much farther than any previous measurement. An analysis of the signal shows how the hydrogen is clumped in space, which turns out to be in general agreement with other methods of mapping out the large scale structure of matter in the universe.
“This is the measurement CHIME was designed to do,” Dr. Halpern said.
Team members said the result was harder to obtain than expected in part because the combined radio noise emitted by electrons careening around the Milky Way is up to ten thousand times stronger than the faint hydrogen signal in the background.
“You want to subtract a very large signal to detect a very faint signal,” said Arnab Chakraborty, a postdoctoral researcher at the University of Toronto’s Dunlap Institute, who worked with the data.
He added another challenge is the radio environment around the observatory, which, in spite of restrictions, is increasingly inundated with human-generated radio interference thanks to the proliferation of electronics in cars and personal devices that are in constant contact with the internet.
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To obtain their result, the team began with data gathered over 2,000 days and whittled it down to just 94 days without radio interference during which conditions were ideal for sensing signals of cosmic hydrogen.
Dr. Chakraborty said that he and others worked with the data for more than two years to satisfy themselves that what they were seeing is real.
In order to filter out unwanted radio noise, the team had to remove the data that would show how the separation between large clouds of hydrogen was changing billions of years ago. If this can be restored with future analysis, it will enable an estimate of the strength of dark energy at that earlier time in the universe’s history.
CHIME is among a few facilities worldwide “with huge potential” to use hydrogen for revealing the history and nature of the universe, said Will Percival, an astrophysicist at the University of Waterloo who was not part of the collaboration.
“This was not an easy signal to tease out of the data,” he added. “Kudos to the CHIME team for getting this result.