This image from a supercomputer simulation shows the density of dark matter in our Milky Way galaxy which is known to contain an ancient thin disk of stars. Brightness (blue-to-violet-to-red-to-yellow) corresponds to increasing concentration of dark matter. The bright central region corresponds roughly to the Milky Way's luminous matter of gas and stars and the bright clumps indicate dark-matter satellites orbiting our Milky Way galaxy, which are known as "substructure". The simulation predicts that the dark-matter halos of spiral galaxies are lumpy, filled with hundreds of dark matter substructures that pass through the stellar disks of galaxies, leaving their imprint and disturbing them in the process.
Credit: Stelios Kazantzidis, Ohio State University