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The cooling flow problem is one of the central problems in galaxy clusters,and active galactic nucleus (AGN) feedback is considered to play a key role inoffsetting cooling. However, how AGN jets heat and suppress cooling flowsremains highly debated. Using an idealized simulation of a cool-core cluster,we study the development of central cooling catastrophe and how a subsequentpowerful AGN jet event averts cooling flows, with a focus on complexgasdynamical processes involved. We find that the jet drives a bow shock, whichreverses cooling inflows and overheats inner cool core regions. The shocked gasmoves outward in a rarefaction wave, which rarefies the dense core andadiabatically transports a significant fraction of heated energy to outerregions. As the rarefaction wave propagates away, inflows resume in the clustercore, but a trailing outflow is uplifted by the AGN bubble, preventing gasaccumulation and catastrophic cooling in central regions. Inflows and trailingoutflows constitute meridional circulations in the cluster core. At latertimes, trailing outflows fall back to the cluster centre, triggering centralcooling catastrophe and potentially a new generation of AGN feedback. We thusenvisage a picture of cool cluster cores going through cycles ofcooling-induced contraction and AGN-induced expansion. This picture naturallypredicts an anti-correlation between the gas fraction (or X-ray luminosity) ofcool cores and the central gas entropy, which may be tested by X-rayobservations.

Reversing cooling flows with AGN jets: shock waves, rarefaction waves, and trailing outflows