Satellite galaxy
From Tardis Wiki, the free Doctor Who reference
Satellite Galaxies, also called Dwarf Galaxies, were small galaxies that orbited larger galaxies. They contained many stars, but not as many as a larger galaxy.
Mutter's Spiral had a satellite galaxy called Galaxy Seven, which was likely its seventh satellite galaxy. (NSA: The Eyeless).
In 4126, the Tenth Doctor and Donna Noble were shown a map of the Tri-Galactic that was controlled by the Second Great and Bountiful Human Empire. It likely included satellite galaxies, the Andromeda Galaxy and possibly others as well. (DW: Planet of the Ood)
In the 43rd century, Humans colonised the Canis Major Dwarf galaxy, likely another satellite of Mutter's Spiral. (DWBIT: #45)
