|Cannibal Background Information: Satellite Galaxies|
Most large galaxies like our Milky Way are surrounded by satellite companion galaxies. These companion galaxies are small (typically a few kiloparsecs or less in size) and low in mass (107 - 109 solar masses, or 0.1% - 10% the mass of the big galaxy). They come in a variety of types, from irregular galaxies like the Large Magellenic Cloud, a companion of the Milky Way, to dwarf elliptical companions like M32 and NGC 205, which accompany the nearby Andromeda galaxy.
The gravitational pull from the larger parent galaxy keeps these satellite traveling on bound orbits around their parent. These orbits can be highly elliptical, such that the satellites pass through the inner regions of the parent, then back to the outskirts, repeatedly over hundreds of millions or billions of years.
While all but the largest companions are too low in mass to seriously affect the parent galaxy, the companions themselves are greatly changed by the interaction with the parent. Through a process called "dynamical friction", the companion will slowly spiral in nearer and nearer to the center of the parent. As it moves inwards, the gravitational tidal force of the parent strips stars from the companion, slowly "eating away" the low mass companion. An example of this is the recently discovered Sagittarius dwarf galaxy in our own Milky Way