 The mass of the Andromeda Galaxy is estimated to be 1.5 × 1012 solar masses, while the Milky Way is estimated to be 8.5 × 1011 solar masses. In comparison, a 2009 study estimated that the Milky Way and M31 are about equal in mass, while a 2006 study put the mass of the Milky Way at ~ 80 % of the mass of the Andromeda Galaxy. The Milky Way and Andromeda are expected to collide in 3.75 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disc galaxy.
