Theories of Large Scale Structure of the Universe, galaxies and clusters of galaxies. These are so-called HOT clusters. Many of these show evidence for ongoing mergers in them, e.g., Coma, and are not relaxed systems. Watanabe et al. A number of these have high gas densities in their cores, as result the radiative efficiency is high and leads to cooling time scales shorter than the Hubble time.
CFs are usually prevalent among POOR clusters and groups.
Presence of a CF component should be included in the analysis of X-ray spectral and imaging data. It, therefore, seems fair to say that the natural state for a regular cluster is the one that has a CF in its centre. Inaccuraces in the plasma physics resulting from poor knowledge of the atomic physics in the codes used to analyse the X-ray data. Below we give examples of controversial results due to above deficiencies. The results are now consistent with the other experiments.