Messier 81 is a spiral galaxy in approx. 12 million light-years distance. It is about half the size of our home galaxy. Holmberg IX, a young dwarf satellite galaxy, is to the left of M 81.
M 81's companion galaxy M 82 to the right is the closest example of a star-burst galaxy. At least one close encounter with M 81 triggered a tremendous increase of star birth in its inner region, resulting in many super novae, which pushed out a high amount of exited gas from the galaxy's center.
Above image also shows some galactic 'cirrus', interstellar dust within our galaxy, illuminated by the combined light of the Milky Way.