This illustration shows the disk of our Milky Way Galaxy surrounded by a fain, extended halo of old stars. Astronomers using the Hubble Space Telescope to observe the nearby Andromeda Galaxy serendipitously identified a dozen foreground stars in the Milky Way halo. They measured the first sideways motions (represented by the arrows) for such distant halo stars. The motions indicate the possible presence of a shell in the halo, which may have formed from the accretion of a dwarf galaxy. This observation supports the view that the Milky Way has undergone continuing growth and evolution over its lifetime by consuming smaller galaxies. // NASA/ESA/and A. Feild (STScI)