The two insets are Hubble Space Telescope images of a normal dwarf galaxy (upper left) and a recently discovered ultra-compact dwarf galaxy (lower right). The object running diagonally in the middle is a star trail that would result from a tidal disruption of the halo of a normal dwarf galaxy, producing a compact dwarf galaxy. The background shows the Fornax galaxy cluster, where seven ultra-compact dwarf galaxies have been found.