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 .
In comparison , a 2009 study estimated that the Milky Way and Andromeda are about equal in mass , while a 2006 study put the mass of the Milky Way at ~ 80 % of the mass of Andromeda .