Astronomers have created the largest three-dimensional map of hydrogen emission from the early universe, revealing cosmic structures that existed between 9 and 11 billion years ago when star formation was at its peak.
The map captures a period often referred to as the universe’s “cosmic noon” and was assembled using data from the Hobby-Eberly Telescope Dark Energy Experiment, or HETDEX.
The project maps the faint Lyman-alpha ultraviolet glow of hydrogen that exists between galaxies. Researchers describe this diffuse hydrogen emission as a “sea of light” that is normally invisible until reconstructed through mapping.
To build the map, the team used a technique known as line intensity mapping. The method combines more than 600 million spectra collected by HETDEX into a three-dimensional heat map of cosmic hydrogen. The experiment operates on the Hobby-Eberly Telescope in Texas, where spectrographs capture the large dataset used in the study.
Unlike traditional surveys that catalogue galaxies one by one, intensity mapping measures the combined Lyman-alpha emission across large regions of the sky. By correlating the positions of bright galaxies with the faint hydrogen glow, astronomers were able to identify vast structures in the early universe that earlier surveys, which focused mainly on bright objects, could not detect.
Researchers say the map provides new insight into how galaxies accumulated gas, formed new stars, and merged into large-scale structures during the peak era of star formation. The findings also offer an important tool for studying how galaxies evolved over time.
The project marks an early step in a new generation of surveys that use intensity mapping to reveal the broader glowing structure of the cosmos rather than only its brightest regions.
Co-author Caryl Gronwall said the study represents an exciting first step toward understanding the processes involved in how galaxies form and evolve.