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

TL;DR

This paper validates a new theory that stellar wind bubbles in turbulent clouds cool efficiently and are momentum-driven, using 3D hydrodynamic simulations that match theoretical predictions across various densities.

Contribution

The study confirms the theory of efficient cooling and momentum-driven evolution of stellar wind bubbles through detailed simulations, highlighting the fractal interface and turbulent mixing effects.

Findings

Cooling is highly efficient and generic in turbulent star-forming clouds.

Bubble expansion velocities are much lower than classical models predict.

The bubble/cloud interface is fractal with dimension ~2.5-2.7.

Abstract

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 Weaver77 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 ~ 1.2-4. We verify that the bubble/cloud interface is a fractal with dimension ~ 2.5-2.7. The measured turbulent amplitude (v_t ~ 200-400 km/s) 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 ~ 0.1-0.01, decreasing with time, explaining observations that indicate low hot-gas content and weak dynamical effects of stellar winds.