Galaxy in a dark matter halo

Image of a spiral galaxy surrounded by a blue cloud representing the dark matter halo
Artist’s impression of a spiral galaxy embedded in a larger distribution of invisible dark matter, known as a dark matter halo (coloured in blue). Studies looking at the formation of dark matter haloes have suggested that each halo could harbour a very dense nucleus of dark matter, which may potentially mimic the effects of a central black hole, or eventually collapse to form one.
ESO / L. Calçada