galactic halo

noun

1. astronomy a spheroidal aggregation of globular clusters, individual stars, dust, and gas that surrounds the Galaxy

galactic halo

1. A large, spherical region of relatively dust-free space surrounding a spiral galaxy such as the Milky Way. The inner regions of the galactic halo contain globular clusters of very old stars, while the outer regions are apparently occupied by large amounts of dark matter.
2. See also MACHO