Artwork showing the approximate extent of the dark matter halo around a large spiral galaxy such as our own. Credit: Jose Wudka.
The dark halo is the massive outer region of the Milky Way Galaxy that surrounds the disk and stellar halo. The dark halo consists mostly of dark matter, whose form is unknown. Though it emits almost no light, the dark halo outweighs the rest of the Galaxy by a factor of approximately 20 to 1. Similar halos of nonluminous matter appear to surround and envelope other large galaxies. See also galactic halo.