The hydrodynamics of Type II supernovae

Abstract

The evolutionary phases of an explosion in a star with an extended envelope, which could produce the moderately cool expanding photosphere indicated in observations of Type II supernovae are described. The propagation of the shock wave through the star is studied from gamma = 4/3 blast wave solutions. If the photon mean free path becomes large compared to the length scales of the flow, a thermal wave moves out from the shock wave and a dense shell is formed behind the shock. The arrival of the shock wave at the photosphere is accompanied by ultraviolet and X-ray bursts. As the star expands, a rarefaction wave converts internal energy into kinetic energy. Detailed hydrodynamic models have been calculated, assuming an initial radius compatible with stellar evolution and an energy compatible with the observed velocities. The observed values of photospheric radius and temperature near maximum light are reproduced. Features of the models which are consistent with observation are: the ejection of a detached shell; the rate of photosphere cooling; the shape of the light curve around maximum; the decrease in the velocity of the gas at the photosphere in tens of days after maximum; and the photospheric radius after several hundred days.