Complex Physics in Cluster Cores: Showstopper for the Use of Clusters for Cosmology?

The influence of cool galaxy cluster cores on the X-ray luminosity--gravitational mass relation is studied with Chandra observations of 64 clusters in the HIFLUGCS sample. As preliminary results we find (i) a significant offset of cool core (CC) clusters to the high luminosity (or low mass) side compared to non-cool core (NCC) clusters, (ii) a smaller scatter of CC clusters compared to NCC clusters, (iii) a decreasing fraction of CC clusters with increasing cluster mass, (iv) a reduced scatter in the luminosity--mass relation for the entire sample if the luminosity is scaled properly with the central entropy. The implications of these results on the intrinsic scatter are discussed.