galactic halo

The term galactic halo is used to denote an extended, roughly spherical component of a galaxy, which extends beyond the main, visible component. It can refer to any of several distinct components which share these properties:the galactic spheroid (stars)the galactic corona (hot gas, i.e. a plasma) the dark matter halo
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The spherical region around our own and other spiral galaxies which consists of dim stars, brown dwarfs and the stellar collections known as globular clusters. Its radius is that of the parent galaxy although, since it is a sphere instead of a disc, its volume is much greater.