Observed stars and gas account for only part of the ordinary, or baryonic, matter inferred from measurements of the early universe. The CHIME/FRB collaboration used the frequency-dependent delay caused by ionized gas as a sensitive probe of this hard-to-see material.

Researchers statistically compared the dispersion of 2,870 fast radio bursts with more than six million galaxy positions from DESI. They found very diffuse, extended reservoirs around galaxies and galaxy groups, reaching roughly four million light-years from galaxies according to the university summary.

The result concerns ordinary matter made of protons and neutrons, not mysterious dark matter. This is a first application of the specific cross-correlation method, and larger burst catalogues should improve the map.