Efficiently Cooled Stellar Wind Bubbles in Turbulent Clouds. II. Validation of Theory with Hydrodynamic Simulations

In a companion paper, we develop a theory for the evolution of stellar wind-driven bubbles in dense, turbulent clouds. This theory proposes that turbulent mixing at a fractal bubble/shell interface leads to highly efficient cooling, in which the vast majority of the input wind energy is radiated away. This energy loss renders the majority of the bubble evolution momentum driven rather than energy driven, with expansion velocities and pressures orders of magnitude lower than in the classical Weaver et al. solution. In this paper, we validate our theory with three-dimensional, hydrodynamic simulations. We show that extreme cooling is not only possible, but is generic to star formation in turbulent clouds over more than three orders of magnitude in density. We quantify the few free parameters in our theory, and show that the momentum exceeds the wind input rate by only a factor alpha(p) similar to 1.2-4. We verify that the bubble/cloud interface is a fractal with dimension similar to 2.5-2.7. The measured turbulent amplitude (v(t) similar to 200-400 km s(-1)) in the hot gas near the interface is shown to be consistent with theoretical requirements for turbulent diffusion to efficiently mix and radiate away most of the wind energy. The fraction of energy remaining after cooling is only 1 - Theta similar to 0.1-0.01, decreasing with time, explaining observations that indicate low hot-gas content and weak dynamical effects of stellar winds.

Automated summary

This study presents a theory on the evolution of wind-driven bubbles in dense, turbulent clouds, and validates it through simulations. It demonstrates the possibility of extreme cooling and explains the low hot-gas content and weak dynamical effects of stellar winds observed in turbulent clouds.