Milky Way 50 Percent Larger, Astronomers Discover

[N]ew measurements of how quickly our galaxy is rotating have led a team of Harvard astrophysicists to conclude that our galaxy is 50 percent more massive than previously thought, and likely does have four arms.

“We should certainly think of the Milky Way no longer as the little sister of the local group,” said Mark Reid of the Harvard-Smithsonian Center for Astrophysics. “We should think of the Milky Way and Andromeda as more like fraternal twins.”