The dark halo of the Milky Way

Most of the matter in the Milky Way is invisible to astronomers. Precise nu mbers are elusive, but it appears that the dark component is 20 times as ma ssive as the visible disk of stars and gas. This dark matter is distributed in space differently than the stars, forming a vast, diffuse halo, more sp herical than disklike, which occupies more than 1000 times the volume of th e disk of stars. The composition of this dark halo is unknown, but it may c omprise a mixture of ancient, degenerate dwarf stars and exotic, hypothetic al elementary particles.