Cosmic Background Explorer satellite map of tiny variations in the Cosmic Background Radiation, representing vast structures present in the universe since the big bang. But Dr Staveley-Smith's study shows that at about 250 million light years beyond the Milky Way, dwarf galaxies appear much more evenly distributed than the bright ones. But they remain absent from the largest voids. This observation gels with theories of galaxy formation, where the bright objects in galaxies are embedded in a sea of cold dark matter. Galaxies only form at the 'peaks' of the CDM density distributions.
Larger galaxies form from larger peaks and thus are more clumped than fainter dwarf galaxies.
For example, density peaks will be higher if there is an underlying large spatial scale density fluctuation. Where there is a negative large spatial scale fluctuation, those same density peaks will not stand out as much, thus creating a void. A related study with the Parkes telescope has found over 100 bright galaxies behind the Milky Way, forming long lines and sheets which join up with known structures. Dr Staveley-Smith and colleagues are also trying to locate the Great Attractor. This is an immense gravitational source, probably a huge cluster of galaxies, pulling the Milky Way and neighbouring galaxies towards it at 600 km per second.