A Canadian radio telescope has independently detected the faint 21-centimeter glow of neutral hydrogen from a time when the universe was about five billion years old. The result gives cosmologists a new way to map matter across immense volumes of space and, eventually, to test competing explanations for dark energy.
The Canadian Hydrogen Intensity Mapping Experiment, or CHIME, was built in British Columbia to map the large-scale distribution of hydrogen in the universe. Until now, its cosmological hydrogen measurements depended on cross-correlation with optical galaxy surveys. The new work, published in The Astrophysical Journal and announced by the University of British Columbia on September 28, shows that CHIME can recover the cosmological hydrogen signal using its own radio data.
Hydrogen is useful because it is the most abundant element in the universe. Neutral hydrogen emits radio waves at a characteristic wavelength of 21 centimeters. Cosmic expansion stretches that signal to longer wavelengths, so astronomers can use its observed frequency to infer how far back in cosmic history the emission originated. Rather than resolving individual galaxies, intensity mapping adds together the weak emission from huge regions of space to trace how matter is distributed.
The signal was extracted from 94 nights of observations collected in 2019. Researchers then spent more than a year testing whether the detection could instead be explained by instrumental effects, foreground radio emission or human-made interference. According to the team, the signal survived those checks. An accompanying analysis indicates that roughly two percent of hydrogen was in neutral atomic form at the epoch being observed, broadly consistent with other measurements.
The broader significance is dark energy. By measuring how matter clusters at different distances and epochs, astronomers can reconstruct how the expansion rate of the universe has changed. CHIME was designed to make this kind of survey across enormous areas of sky at lower cost than conventional optical galaxy mapping. A standalone hydrogen detection means the technique can now begin to function as an independent cosmological probe rather than merely confirming structures already mapped by other instruments.
The current result is still an early step, not a new measurement of dark energy itself. It uses only a small fraction of the data CHIME has accumulated. The collaboration now has nearly seven years of observations and is working toward measurements from an earlier era, when the universe was only about three billion years old. Larger datasets and tighter control of systematic errors will be required before the method can distinguish between competing cosmological models.
That is what makes the result philosophically interesting as well as technically important. Much of cosmic history is invisible to ordinary telescopes, yet the universe preserves traces of its evolution in extremely weak background signals. Mapping ancient hydrogen turns those traces into a history of structure and expansion. It is another example of cosmology reconstructing the past not by seeing individual objects, but by reading patterns left across the universe as a whole.
For related coverage, see Templum Dianae’s report on recent evidence in the search for dark matter.
References
https://doi.org/10.3847/1538-4357/ae9835
https://commons.wikimedia.org/wiki/File:CHIME_experiment_construction_-_2015-07-16.jpg
