DYNAMICS OF WIND BUBBLES AND SUPERBUBBLES .1. SLOW WINDS AND FAST WINDS

Steady injection of mass and energy into an ambient medium produces a wind-blown bubble. This paper describes the overall evolution of such bubbles in a uniform medium from the initial, free-expansion stage to the final stage in which the pressure of the ambient medium is significant. We introduce the concepts of slow and fast winds, which naturally arise from consideration of radiative losses in the free-expansion stage. Bubbles blown by slow winds are radiative; bubbles blown by young stellar objects are the prototype. Provided the wind velocity is not too small, such bubbles evolve into partially radiative bubbles after the radiative stage. Bubbles blown by fast winds, on the other hand, are adiabatic by the time the swept-up gas dominates the gas injected by the wind, and they remain adiabatic unless there is additional mass injection into the bubble; bubbles blown by winds from OB stars are the prototype. Bubbles blown by either slow winds or fast winds eventually expand to the point that the pressure of the ambient medium is significant, and become pressure-confined bubbles. We also consider the evolution of bubbles in a plane-parallel disk, where the density decreases steeply along a vertical direction. We discuss when a bubble can break out a thin galactic disk, and how they evolve after the breakout. After breakout, bubbles can evolve into jets. Steady, collimated jets can form only over a limited range of wind luminosity and Mach number; astronomical jets are likely to be unsteady and/or hydromagnetic. Our results are applied to the neutral stellar wind in the HH 7-11 region, to the north polar spur, and to the galactic winds in starburst galaxies.