2005ApJ...622..847S

We propose a scenario in which a large fraction or even most of the gas cooling to low temperatures of T<10⁴ K in cooling flow clusters gains energy directly from the central black hole. Most of the cool gas is accelerated to nonrelativistic high velocities, v_j≃10³-10⁴ km/s, after flowing through, or close to, an accretion disk around the central black hole. A poorly collimated wind (or a pair of poorly collimated opposite jets) is formed. According to the proposed scenario, this gas inflates some of the X-ray-deficient bubbles, such that the average gas temperature inside these bubbles (cavities) in cooling flow clusters is kT_b≲100 keV. A large fraction of these bubbles will be very faint or undetectable in the radio. The bright rims of these weak smaller bubbles will appear as ripples. We suggest that the X-ray ripples observed in the Perseus cluster, for example, are not sound waves but rather the rims of radio-faint weak bubbles that are only slightly hotter than their environment. This scenario is incorporated into the moderate cooling flow model; although not a necessary ingredient in that model, it brings it to better agreement with observations. A cooling flow does exist in the moderate cooling flow model, but the mass cooling rate is ≲10% of that in old versions of cooling flow models.