Multi-Dimensional Radiation/Hydrodynamic Simulations of Protoneutron Star Convection
Abstract
Based on multi-dimensional multi-group radiation hydrodynamic simulations of core-collapse supernovae with the VULCAN/2D code, we study the physical conditions within and in the vicinity of the nascent protoneutron star (PNS). Conclusions of this work are threefold: First, as before, we do not see any large-scale overturn of the inner PNS material. Second, we see no evidence of doubly-diffusive instabilities in the PNS, expected to operate on diffusion timescales of at least a second, but instead observe the presence of convection, within a radius range of 10-20 km, operating with a timescale of a few milliseconds. Third, we identify unambiguously the presence of gravity waves, predominantly at 200-300 ms past core bounce, in the region separating the convective zones inside the PNS and between the PNS surface and the shocked region. PNS convection is always confined to a region between 10 and 20 km, i.e., within the neutrinospheric radii for all neutrino energies above just a few MeV. We find that such motions do not appreciably enhance the electron neutrino luminosity, and that they can enhance the anti-electron and "mu" neutrino luminosities by no more than ~15% and ~30%, respectively, during the first post-bounce ~100 ms, after which the optical depth barrier between the inner convection and the neutrinospheres effectively isolates one from the other, terminating even this modest enhancement. PNS convection is thus found to be a secondary feature of the core-collapse phenomenon, rather than a decisive ingredient for a successful explosion. (abridged)Keywords
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