5.3. Cold Dark Matter
The difficulties of the neutrino-dominated model became evident in early 1980s. A new scenario was suggested by Blumenthal, Pagels & Primack (1982), Bond, Szalay & Turner (1982), and Peebles (1982); here hypothetical particles like axions, gravitinos or photinos play the role of dark matter. Numerical simulations of structure evolution for neutrino and axion-gravitino-photino-dominated universe were made and analysed by Melott et al. (1983). All quantitative characteristics (the connectivity of the structure, the multiplicity of galaxy systems, the correlation function) of this new model fit the observational data well. This model was called subsequently the Cold Dark Matter (CDM) model, in contrast to the neutrino-based Hot Dark Matter model. Presently the CDM model with some modifications is the most accepted model of the structure evolution. The properties of the Cold Dark Matter model were analysed in detail in the classical paper by Blumenthal et al. (1984). With the acceptance of the CDM model the modern period of the study of dark matter begins.
Numerical simulations made in the framework of the Cold Dark Matter Universe (with and without the cosmological -term) yield the distribution of galaxies, clusters and superclusters in good agreement with observations. These studies are too numerous to be cited here. Also the evolution of the structure can be followed by comparison of results of simulations at different epochs. During the School a movie was demonstrated showing the evolution of a central region of a supercluster (the movie was prepared at the Astrophysical Institute in Potsdam). Here the growth of a rich cluster of galaxies at the center of the supercluster could be followed. The cluster had many merger events and has "eaten" all its nearby companions. During each merger event the cluster suffers a slight shift of its position. As merger galaxies come from all directions, the cluster sets more and more accurately to the center of the gravitational well of the supercluster. This explains the fact that very rich clusters have almost no residual motion in respect to the smooth Hubble flow. According to the old paradigm galaxies and clusters form by random hierarchical clustering and could have slow motions only in a very low-density universe (an argument against the presence of large amount of dark matter by Materne & Tammann 1976).