Researchers operating the Canadian Hydrogen Intensity Mapping Experiment telescope have successfully mapped neutral hydrogen from about 5 billion years ago using solely the instrument’s own data, bypassing the need for external optical galaxy catalogs.
Mapping Cosmic Signals Without External Maps
Located in British Columbia, Canada, the CHIME radio telescope measures the clustering of hydrogen gas across the observable universe through 21cm intensity mapping. This technique traces neutral hydrogen clouds to probe the distribution of matter and investigate dark energy, the mysterious force driving the accelerated expansion of the universe. Cosmologists currently focus on three primary scenarios for the ultimate fate of the cosmos: eternal expansion, where the universe continues expanding forever at an accelerating rate without ever reaching a critical catastrophic milestone; the big rip, where dark energy grows increasingly intense over time causing galaxy clusters to tear apart first, followed by individual galaxies, stars, planets, and finally even atoms themselves; and the big crunch, which is the exact opposite of the big rip. Until recently, relying on the method required cross-referencing telescope data with expensive optical galaxy maps produced by other instruments.
Software upgrades implemented by an international team of scientists have removed that dependency. Researchers tested the optimized software using observation data gathered over 94 nights in 2019.
The resulting measurements allowed the team to detect a hydrogen glow from an era when the universe was less than half its current age.
Professor Simon Foreman, an assistant professor in ASU’s Department of Physics, noted the significance of the achievement. We have measured the clustering of hydrogen solely using CHIME data, without relying on other telescopes to tell us where to look,
he said. This is the second-ever measurement of this type by any telescope, and the first measurement of hydrogen clustering when the universe was less than half of its current age.
Refining Galactic Distribution Models
Arizona State University postdoctoral research scholars Shabbir Shaikh and Albin Joseph helped lead a secondary study connecting the CHIME measurements to physical models of how neutral hydrogen distributes itself within galaxies. Their analysis demonstrated that astrophysical data can be reliably extracted from intensity mapping at nonlinear scales.
Like a fingerprint, the strength and shape of this signal reveal how much hydrogen filled the universe about 8 billion years ago and how it was clustered,
Albin Joseph said.
Independent data collection allows researchers to test competing theories regarding dark energy without inheriting external calibration biases. According to Shabbir Shaikh, the initial findings already highlight discrepancies with current models. We already see that the observed clustering measurement disagrees with some state-of-the-art galaxy formation simulations. This indicates the need for further investigation into how neutral hydrogen is distributed in galaxies,
he said.
Tracking Parallel Breakthroughs in South Africa
Operating each dish as an independent telescope rather than combining its 64 dishes into a single interferometer, the team traded sharp angular resolution for very high survey speed and analyzed observations across approximately 250 square degrees of the sky—roughly the area of 1250 full moons.
That signal originated roughly 4.5 billion years ago, when the universe was a little older than 9 billion years. Dr Steven Cunnington, Senior Research Fellow at the University of Portsmouth’s Institute of Cosmology and Gravitation, led the development of the analysis pipeline that enabled the detection. Members of the MeerKLASS collaboration held their bi-annual meeting ‘Busy Week’ hosted at the University of Torino in September 2025. Since rejoining the University of Portsmouth as a Stephen Hawking Fellow in April 2025, Dr Cunnington has also co-led one of the largest working groups within the international MeerKLASS Collaboration. The paper detailing this work is published in Monthly Notices of the Royal Astronomical Society, featuring authors from the MeerKLASS Collaboration alongside Matilde Barberi-Squarotti, José L. Bernal, Philip Bull, Stefano Camera, Isabella P. Carucci, Zhaoting Chen, Steven Cunnington, Brandon N. Engelbrecht, José Fonseca, Keith Grainge, Wenkai Hu, Melis O. Irfan, Yichao Li, Mário G. Santos, Marta Spinelli, Jingying Wang, Amadeus Witzemann, and Laura Wolz, submitted on 8 October 2026.
This result feels particularly special because it’s the culmination of a journey that began when I started my PhD at Portsmouth over a decade ago. I am now fortunate to be part of a much wider international collaboration sharing this common goal.
Dr Steven Cunnington, Senior Research Fellow at the University of Portsmouth
Extracting the MeerKAT signal required overcoming astrophysical foreground emissions roughly 10,000 times stronger than the hydrogen signal itself. Professor Mário Santos, Principal Investigator of the MeerKLASS survey at the University of the Western Cape, emphasized the scale of the effort.
This is a milestone in establishing 21-cm intensity mapping as a novel tool for cosmology
Professor Mário Santos, Principal Investigator of the MeerKLASS survey at the University of the Western Cape
With initial detections now achieved by multiple international collaborations using independent telescope systems, researchers plan to scale up their analysis using accumulated multi-year datasets to further examine the expansion history of the universe. With future data from CHIME and other telescopes, we will be able to push these measurements back even further in time and map out the dark energy-dominated era with unprecedented precision,
Foreman said.