Clusters of Galaxies: Physics, Evolution and Cosmology

Clusters of galaxies - the largest bound structures - can reveal the origin, the evolution and the future of the universe. A cluster is an accumulation of hundreds of galaxies. The space between the galaxies is filled with hot gas, which emits radiation of such high energy, that it is visible in the X-ray range. In particular observations with the new X-ray satellites XMM and CHANDRA are therefore crucial for cosmological research. Most of the mass in the universe is not visible and therefore called dark matter. With clusters of galaxies the amount and the distribution of this dark matter can be measured indirectly. Not only X-ray observations but also the gravitational lensing effect can be used for these studies. Gravitational lensing distorts the images of galaxies situated behind clusters. Hence the position and the shape of the distorted images yield information on the dark matter. With an accurate knowledge of the dark matter a fundamental parameter can be determined - the density of the universe. This parameter decides whether the universe will expand forever or will contract and collapse eventually. The gas between the galaxies contains also heavy elements like e.g. iron. Such heavy elements must have been produced in the stars of galaxies and then they must have been transported into the gas. As the transport processes are not well understood so far, numerical simulations will be performed , which take into account all the possible transport processes. Also these studies are connected with cosmology as the simulations will yield insight into the formation of galaxies and clusters. Clusters of galaxies are relatively young objects, which still contain information about their formation process. Many clusters are not yet in an equilibrium state, but are still in the process of merging. As various cosmological models predict different cluster evolution timescales, the determination of the dynamical state is therefore another way to constrain cosmological parameters with clusters. In this comprehensive project many different methods to constrain cosmological models will be applied using clusters of galaxies as diagnostic tools. The combination of all of these methods will provide deep insights into the origin and the evolution of the universe.