Lyman-alpha forest

The Lyman-alpha forest is a series of absorption lines seen in the spectra of distant galaxies and quasars. These lines occur when light from these objects passes through clouds of hydrogen gas in the universe. Specifically, hydrogen atoms absorb light at a specific wavelength called Lyman-alpha. As a result, we see a "forest" of these absorption features, which can tell us about the distribution and density of hydrogen in the universe. Studying the Lyman-alpha forest helps astronomers understand the structure and evolution of the cosmos over time, providing insight into how galaxies and matter are distributed in space.