Galactic archaeologists find stars in the Milky Way came from another galaxy 12 billion years ago

An illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger Look up on a dark night and the Milky Way appears as a calm band of stars across the sky. But our galaxy has a violent past. For more than 13 billion years it has grown through star formation and mergers with other galaxies. We already know that…