Glowing filaments of the cosmic web

Most gas in the Universe lies in the intergalactic medium, where it forms into sheets and filaments of the cosmic web. Clusters of galaxies form at the intersection of these filaments, fed by gas pulled along them by gravity. Although this picture is well established by cosmological simulations, it has been difficult to demonstrate observationally. Umehata et al. mapped emission from the intergalactic medium in an area around galaxies that are starting to form a cluster (see the Perspective by Hamden). They found that the gas is arranged into filaments, whose position and velocity correlate with star-forming galaxies, supporting the theoretical picture.

Science, this issue p. 97; see also p. 31