M101 is a comparable in size to the Milky Way. The disk is 100 billion solar masses, and the central bulge of about 3 billion solar masses. M101 is rich is pinkish star forming regions, many of which are very large and bright. Unlike most spiral galaxies, M101spiral shape is notably asymmetrical. This is due to the tidal forces from interactions with its companion galaxies. These gravitational interactions compress interstellar hydrogen gas, which then triggers strong star formation activity in M101's spiral arms.
Video: NASA, ESA, and G. Bacon (STScI);
Image: NASA, ESA, K. Kuntz (JHU), F. Bresolin (University of Hawaii), J. Trauger (Jet Propulsion Lab), J. Mould (NOAO), Y.-H. Chu (University of Illinois, Urbana), and STScI
Publication: June 18, 2018