A gravitational contribution to the cooling flow problem

X-ray spectra of cooling flow clusters have shown that the gas temperature drops by about a factor of 3 over the central region where the radiative cooling time drops to 10(8) yr or less, yet does not appear to cool further. This cooling flow problem can be solved by a well-matched, distributed energy source throughout the inner region of a cluster. Here it is proposed that the gravitational potential of the cluster (and central giant galaxy) can contribute to that source. The intracluster medium is assumed to be magnetized and so thermally unstable and, crucially, overdense blobs are assumed to slip from the flow and fall inward. The gravitational accretion energy which would be released locally in a comoving flow is instead dissipated nearer the centre, offsetting the cooling there. The energetics of the process are studied here for the case of A2199. The virial theorem leads to the thermal and gravitational energies being well-matched in all clusters and groups. Evidence for the infall of lower metallicity gas in cluster cores may be found in the off-centre abundance peaks of several well-studied clusters.