Our galaxy the Milky Way is part of a cluster of galaxies called the local group and these galaxies orbit and interact with each other under the force of gravity.
One of the most interesting galaxies in the local group is the Andromeda galaxy. It is generally regarded as a twin of our own Milky Way galaxy and it has taught us a great deal about our own galaxy including much about the structure of the Milky Way.
Image credit: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF
Picture of the Andromeda galaxy. Its possible to see many of the same structures
as are found in our galaxy. Clearly visible are the disk and the central bulge.
Its also possible to see a number of the spherical elements and orbital galaxies
that appear like smudged stars around the Andromeda galaxy.