The distribution of the mass of the Milky Way Galaxy is determined by the observed motion of stars and gas in the Galaxy, as well as by the gravitational lensing of distant objects by the Galaxy's mass. The rotation curve of the Milky Way, which plots the velocities of stars and gas as a function of distance from the center of the Galaxy, indicates that there is more mass in the Galaxy than can be accounted for by the observed stars and gas. This suggests the presence of large amounts of dark matter, which is thought to make up most of the mass of the Galaxy. The distribution of visible matter, such as stars and gas, also plays a role in determining the overall mass distribution.
