Neutrino Transport in a Type II Supernova Environment

Abstract

AbstractWe discuss the full problem of neutrino transport in the context of a Type II supernova environment. We describe the “standard model” of Type II supernova, which involves the core collapse and core bounce of an 8 — 20M⊙ star. Although the shock produced in the standard model is supposed to expel the outer layers of the star, this does not happen in the best numerical collapse calculations without considerable numerical tweaking, if at all. In this model, neutrino transport plays an important role. We describe the weakness of the best transport approximation currently used in collapse calculations, the flux-limited diffusion approximation. We investigate the effect of a full transport approach by constructing two different types of model atmospheres, with conditions chosen to closely approximate conditions found in full collapse calculations. The first model is to construct equilibrium plane-parallel hydrostatic neutrino atmospheres. The second is to solve the equations of neutrino hydrodynamics for a spherical shell of matter, with a piston and a source of neutrinos at the lower boundary. We describe in detail the neutrino interactions which are important in the supernova problem. We present the equations of neutrino hydrodynamics and neutrino hydrostatics which are solved in the two models, and emphasize the differences between photon transport and neutrino transport. We describe briefly a “toy” model, the neutrino Eddington atmosphere, which highlights the differences between photon and neutrino atmospheres. We present the results of our model atmosphere calculations for a few selected cases of interest. Finally, we summarize alternatives and extensions to the standard model which are of current interest and may hold the answer to the Type II supernova problem. However, the delicate balance between competing effects suggest that a rigorous calculation of neutrino transport will be required to obtain a definitive answer.