By pinpointing the ages and origins of stars in the Milky Way, astronomers can trace its history. (Credit: Koppelman, Villalobos and Helmi/NASA/ESA/Hubble)

Ten billion years ago, the Milky Way encountered another galaxy in the vast emptiness of space, and consumed it. Dubbed Gaia-Enceladus by astronomers, this stranger was roughly a quarter the Milky Way’s size, and it forever changed the makeup and shape of our home galaxy.

Scientists have had evidence for a while that the Milky Way saw