2004A&A...413..441C

The radiative cooling time of the X-ray-emitting plasma near the center in many clusters of galaxies is shorter than the age of the cluster, but neither the expected large drop in central temperature - nor the expected mass flow towards the pressure-depleted cluster centers - are observed. We propose a solution to these ``cooling flow'' problems wherein energy is supplied to the plasma by hadronic cosmic rays (CRs). The solution requires an energy deposition more intense and more distributed than in conventional CR models, but this alternative model is also successful in describing the origin of CRs, as well as the properties of gamma ray bursts and of the diffuse gamma background radiation. The X-ray energy emitted by clusters is supplied, in a quasi-steady state, by the hadronic CRs, which act as ``warming rays''. The temperature distribution in the intracluster space is successfully predicted from the measured plasma-density distribution. Four other puzzling features of clusters can also be explained in simple terms: the discrepancy between their ``virial'' and ``lensing'' masses, their large magnetic fields, the correlation between their optical and X-ray luminosities, and the non-thermal tail of their X-ray spectrum.