Sombrero galaxy (M104, NGC 4594), Hubble Space Telescope image. This spiral galaxy is seen almost edge-on to Earth. Its disc is seen as a dark band of dust crossing the brighter central bulge. Most of a galaxy's mass is thought to be in the form of dark matter, some of which can be detected when it obscures the light from stars behind it. The Sombrero galaxy lies around 28 million light years from Earth in the constellation Virgo. It is around 50,000 light years across, less than half the width of our Milky Way galaxy. The image is a mosaic of six true-colour images taken by the HST's Advanced Camera for Surveys in spring 2003.