Astronomers Create the Largest 3D Map of the Early Universe’s Hydrogen Glow

The astronomers have unveiled the largest ever three-dimensional map of hydrogen emission from the early universe. The map extends over the period of 9 to 11 billion years ago, during the universe's ‘cosmic noon' when star formation was at its peak, and is assembled from the data collected in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) that maps the faint Lyman-alpha ultraviolet glow of hydrogen between galaxies. The “sea of light” is invisible until this map is drawn.

Mapping the early universe

According to the new paper, the team applied a technique called line intensity mapping, combining over 600 million HETDEX spectra into a 3D “heat map” of cosmic hydrogen. HETDEX runs on the Hobby-Eberly Telescope in Texas, using spectrographs to capture this vast dataset. Instead of cataloguing galaxies one by one, this approach measures the combined Lyman-alpha emission across wide swaths of sky. By correlating bright galaxy positions with the faint hydrogen glow, it uncovered vast structures in the early universe that earlier surveys focused on bright objects could not detect.

Implications for cosmology

By mapping the location of hydrogen at the peak star-forming epoch of the universe, astronomers have learned new things about how galaxies accumulated gas, made new stars, and merged into vast structures. It is also an important tool for studying the evolution of galaxies.

The project also marks the beginning of an era of surveys that use an approach called intensity mapping, which promises to show the entire, glowing structure of the cosmos, rather than just its brightest parts. Caryl Gronwall, co-author of the study, said in a statement, "This study is an exciting first step in using intensity mapping to understand the processes involved in how galaxies form and evolve."