Out own Milky Way Galaxy has a number of small, dwarf galaxy companions. The two most famous and visible are the Large and Small Magellanic Cloud in the southern hemisphere. It has been pretty much a cosmological given that over eons of time smaller dwarf galaxies are absorbed by the largest galaxy in the group and thereby help that galaxy grow larger.
Astronomers have found a dwarf galaxy where this process is occurring and have obtained some great images and data that will help us understand the building of a bigger galaxy. The image below is of dwarf galaxy NGC 4449 and is the first ever to show a the stream of stellar material that is merging with it
Sky Guy in VA