Abstract

Winds from massive stars have velocities of ~1000 km/s or more, and produce hot, high pressure gas when they shock. I present a theory for the evolution of bubbles driven by these winds from star clusters interacting with the turbulent, dense interstellar medium of their natal molecular clouds. A key feature is the fractal nature of the bubble's surface, which strongly enhances losses from the hot gas, through turbulent diffusion and subsequent cooling at temperatures where radiation is maximally efficient. Due to the extreme cooling, the evolution of the bubble is drastically different than the classical Weaver et al. 1977 solution.  We validate our theory and quantify its few free parameters using a suite of three-dimensional hydrodynamic simulations.  We show that the momentum exceeds the wind input rate by only a factor ~ 1.2-4 and verify that the bubble/cloud interface has a fractal dimension of ~2.5-2.7. The measured turbulent amplitude (200-400 km/s) in the hot gas near the interface is consistent with requirements for turbulent diffusion to efficiently mix and cool away most of the wind energy.  The predicted fraction of energy remaining after cooling is only 1-10%, explaining low observed X-ray fluxes from observed wind bubbles. We discuss implications of our theory for observations of stellar winds, and for predictions of feedback-regulated star formation in a range of environments.