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. Image courtesy of Stelios Kazantzidis, Ohio State University.

Density maps of disk stars illustrating the global morphological transformation of a galactic disk subject to bombardment by dark matter substructures. Brighter colors indicate regions of higher density of disk stars. The left panel shows the initial disk, while the right panel depicts the final disk after the violent gravitational encounters with the orbiting substructures. The edge-on (upper panels) and face-on (bottom panels) views of the disk are displayed in each frame. Satellite-disk interactions of the kind expected in the currently favored cosmological model produce several distinctive signatures in galactic disks including: long-lived, low-density, ring-like features in the outskirts; conspicuous flares; bars; and faint filamentary structures above the disk plane that resemble tidal streams. These morphological features are similar to those being discovered in the Milky Way, the Andromeda galaxy, and in other spiral galaxies. Image courtesy of Stelios Kazantzidis, Ohio State University.


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