Figuring out how much stuff is in inside our own galaxy is harder than you might expect. New research shows that the Milky Way we live in is about half the mass of our closest neighbor, Andromeda. It's previously been suggested that the Milky Way is more massive than Andromeda; this research disproves this.
Walker’s team was able to account for the forces of gravity within the Local Group as well as external expansion forces in order to precisely determine the mass of our galaxy and our closest neighbor. Ultimately, they were able to disprove other studies that had claimed the Milky Way to be more massive than Andromeda.