Keynote: Structure of the Universe

Abstract

A clear keynote for our conference is given by the diagram shown in Figure 1. This year we can celebrate that it is just half a century ago that it was produced by Harlow Shapley and Adelaide Ames. This marvellous picture illustrates nearly all we know about the properties of the Universe, except its expansion. It can teach us practically all the lessons we are still learning today. Most prominent is the Virgo cluster. Also evident are structures on larger scale, such as the appendages on both sides of the cluster, spanning a total length of 20 to 30 Mpc.* They are the kernel of the Local, or Virgo, supercluster. The supercluster has a complicated structure, evident from the clumpiness in the distribution along its axis, but likewise from the arrangement of the galaxies in its environment. The centre of the local supercluster (the Virgo cluster) lies at a distance of about 20 Mpc. The supercluster probably extends somewhat beyond us. However, everything in the Shapley-Ames picture should be considered as connected with this one supercluster. Features marked A, B and C may be independent structures; A lies at a distance of roughly 50 Mpc; C, at a distance of ∼ 70 Mpc, lies similarly well outside the Local Supercluster. The strongly elongated feature B, with an average velocity of 1400 km s−1 and a dispersion of only 300 km s−1, appears also well isolated. All three are roughly 30 Mpc long, and may be considered as separate superclusters.