Cosmic rays are generated in galaxies, presumably by supernovae and active galactic nuclei, and are released into the surrounding medium. Theoretical estimates and implications from radio observations suggest that the nuclear component of the cosmic rays may be dynamically important in the intergalactic medium of clusters of galaxies, in particular in compact clusters with cooling flows. We studied the propagation and dynamical role of the cosmic rays in the intracluster gas by means of steady spherically symmetric models. With expected values for the cosmic-ray production rate and the transport coefficients we find that the cosmic-ray pressure may be comparable to the thermal gas pressure in the halo region around central galaxies in clusters with cooling flows. This should result in Rayleigh-Taylor instabilities inducing an inhomogeneous structure in the cooling flow region. These inhomogeneities may be an important trigger for subsequent thermal condensation leading to the formation of filaments and star birth regions.
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Boehringer et al. (1988) studied this question.