This image is a snapshot of a cosmological simulation zoomed on a single galaxy and its environment when the universe was only one billion years old (today the age of the Universe is about 13.8 billion years). This density map traces the gas distribution, clumps in the map represent the central galaxy and their satellites, while filaments are primordial gas inflowing on the compact objects. This numerical simulation is produced by the Cosmology group of the Scuola Normale Superiore.