Heating by Acoustic Waves of Multiphase Media

We study the emission and dissipation of acoustic waves from cool dense clouds in pressure equilibrium with a hot, volume-filling dilute gas component. In our model, the clouds are exposed to a source of ionizing radiation whose flux level varies with time, forcing the clouds to pulsate. We estimate the rate at which acoustic energy is radiated away by an ensemble of clouds and the rate at which it is absorbed by, and dissipated in, the hot dilute phase. We show that acoustic energy can be a substantial heating source of the hot gas phase when the mass in the cool component is a substantial fraction of the total gas mass. We investigate the applicability of our results to the multiphase media of several astrophysical systems, including quasar outflows and cooling flows. We find that acoustic heating can have a substantial effect on the thermal properties of the hot phase in those systems.