星形成
The Milky Way's stellar halo contains globular clusters, RR Lyrae stars with low metal content, and subdwarfs. Stars in our stellar halo tend to be old (most are greater than 12 billion years old) and metal-poor, but there are also halo star clusters with observed metal content similar to disk stars. The halo stars of the Milky Way have an observed radial velocity dispersion of about 200 km/s and a low average velocity of rotation of about 50 km/s. Star formation in the stellar halo of the Milky Way ceased long ago.