Footprints of 'galactic immigration' uncovered in Andromeda galaxy
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Over the course of billions of years, galaxies grow and evolve by forging new stars and merging with other galaxies through aptly named "galactic immigration" events. Astronomers try to uncover the histories of these immigration events by studying the motions of individual stars throughout a galaxy and its extended halo of stars and dark matter. Such cosmic archaeology, however, has only been possible in our own galaxy, the Milky Way, until now.