Multidimensional Radiation/Hydrodynamic Simulations of Proto–Neutron Star Convection

Abstract

Based on multidimensional, multigroup, flux-limited-diffusion hydrodynamic simulations of core-collapse supernovae with the VULCAN/2D code, we study the physical conditions within and in the vicinity of the nascent proto-neutron star (PNS). Our numerical study follows the evolution of the collapsing envelope of the 11 Msolar model of Woosley & Weaver from ~200 ms before bounce to ~300 ms after bounce on a spatial grid that switches from Cartesian at the PNS center to spherical above a 10 km radius. As has been shown previously, we do not see any large-scale overturn of the inner PNS material. Convection, directly connected to the PNS, is found to occur in two distinct regions, between 10 and 20 km, coincident with the region of negative lepton gradient, and exterior to the PNS, above 50 km. Separating these two regions, an interface with no sizable inward or outward motion is the site of gravity waves, emerging at 200-300 ms after core bounce, excited by the convection in the outer convective zone. In the PNS convection is always confined within the neutrinospheric radii for all neutrino energies above just a few MeV. We find that such convective motions do not appreciably enhance the νe neutrino luminosity, and that they enhance the ν¯e and ``νμ'' luminosities modestly by ~15% and ~30%, respectively, during the first postbounce 100-200 ms. Moreover, we see no evidence of doubly diffusive instabilities in the PNS, expected to operate on diffusion timescales of at least a second, much longer than the millisecond timescale associated with PNS convection. PNS convection is thus found to be a secondary feature of the core-collapse phenomenon, rather than a decisive ingredient for a successful explosion.