... ESO, the European Southern Observatory . ... ESO's Governing Bodies . ... Green ESO . ... This artistтАЩs impression shows the Milky Way galaxy. The blue halo of material surrounding the galaxy indicates the expected distribution of the mysterious dark matter, which was first introduced by astronomers to explain the rotation properties of the galaxy and is now also an essential ingredient in current theories of the formation and evolution of galaxies. ... Dark Matter , Milky Way . ... Milky Way . ...