CHIME captured the radio signal from hydrogen dating back to when the universe was about five billion years old, using only its own data.
The method costs a fraction of galaxy surveys in visible light and can be used to test theories of dark energy.
The signal held up after more than a year of tests and also showed up when the researchers split the data into two separate halves.
The CHIME radio telescope in Canada has captured the faint radio signal from hydrogen that existed when the universe was about five billion years old. The signal has traveled for almost nine billion years. This is the first time CHIME has done this with only its own data, without comparing it to maps from other telescopes.
The results are presented in two studies in The Astrophysical Journal. The work was done by researchers from the University of British Columbia, McGill University, the University of Toronto, the National Research Council of Canada (NRC), Arizona State University, and the Raman Research Institute in India.
Hydrogen shows how matter is distributed
Hydrogen is the most common element in the universe and the raw material for stars. The gas gives off radio waves with a wavelength of 21 centimeters (about 8 inches). By measuring the combined glow of hydrogen over large areas, researchers can see how matter is distributed in space.
Such a map can be used to measure how the universe has expanded and to test different theories of dark energy. Dark energy is thought to make up about 70 percent of the universe and to be the reason the expansion is speeding up.
Previously, CHIME had to combine its measurements with galaxy surveys from other telescopes. Those surveys are done in visible light and cost millions more. They also only capture the parts of the universe that are dense and hot enough to form stars. By measuring the radio glow of hydrogen directly, CHIME reaches larger scales and farther back in time, at a fraction of the cost.
More than a year of tests
The analysis is based on 94 nights of observations from 2019. The researchers only used data collected at night, when the sun was below the horizon.
The hydrogen signal is very faint. Radiation from the Milky Way and other sources in space is several orders of magnitude stronger. On top of that comes interference from human-made radio technology and noise from the instrument itself. The team developed new methods to find and remove the interference. In the analysis, the foreground radiation was suppressed by a factor of at least 10,000.
The signal stood out with a statistical significance of 12.4 sigma. This means it was just over twelve times larger than the uncertainty in the measurement. When the researchers split the frequency band into two halves and analyzed each one separately, the signal showed up in both.
Arnab Chakraborty, a postdoctoral researcher at the University of Toronto, was the first to propose the detection. He says the team worked hard to convince themselves that it was not a false alarm. The researchers tested the result for more than a year, and the signal held up after every test.
The analysis uses only a small part of CHIME's data. The researchers have almost seven years of observations and want to use the method all the way back to when the universe was about three billion years old.
Two percent of the hydrogen was neutral
In the second study, the researchers interpret the signal. They calculate that about two percent of the universe's hydrogen existed as neutral atoms at that time. This broadly matches other measurements. According to Shabbir Shaikh, a postdoctoral researcher at Arizona State University, the results offer a new way to test how galaxies form and evolve.
Mark Halpern, a professor at the University of British Columbia and principal investigator for CHIME, describes the method as an entirely new way to study the cosmos. The instrument was conceived, built, and funded in Canada.
A telescope with no moving parts
CHIME is located at the Dominion Radio Astrophysical Observatory near Penticton, British Columbia. The telescope was built in 2017 and consists of four semi-cylindrical reflectors. Each one is 20 meters (about 66 feet) wide and 100 meters (about 330 feet) long, and together they have 1,024 antennas. The telescope has no moving parts. Instead, the rotation of Earth sweeps the sky past it, and CHIME maps the entire northern sky every day.
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