Heating by Acoustic Waves of Multiphase Media

TL;DR

This paper investigates how acoustic waves generated by pulsating clouds in multiphase media can significantly heat the hot gas phase, with implications for astrophysical systems like quasar outflows and cooling flows.

Contribution

It introduces a model for acoustic wave emission and dissipation in multiphase media, highlighting acoustic heating as a substantial energy source for hot gas phases.

Findings

Acoustic energy can heat the hot gas when cool clouds are a significant mass fraction.

The model estimates the energy transfer rates between phases.

Acoustic heating impacts the thermal state of astrophysical multiphase systems.

Abstract

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.