Stellar core collapse. I - Infall epoch

Abstract

We report on simulations of the collapse of the central iron core of 15 M/sub sun/ spherically symmetric star. In this paper we consider the infall epoch, between the onset of collapse and core bounce. The models use the recent equation of state of Lamb, Lattimer, Pethick, and Ravenhall and general-relativistic hydrodynamics. The electron capture rates on nuclei proceed rapidly for densities less than 10/sup 11/ g cm/sup -3/, but are suppressed at higher densities where the neutron number of the nucleus, N, exceeds 40 (Fuller, Fowler, and Newman). We treat neutrino transport by a leakage scheme. The effects of changes in the neutrino trapping density and of qualitative changes in the electron capture reactions on the evolution are explored. Greater lepton loss during collapse leads to larger pressure deficits, more rapid collapse, and smaller inner homologous cores. The entropy change during the infall is small: Vertical Bar ..delta..s Vertical Bar <0.8. The mass of inner core is given, to about 20% by the formula of Goldreich and Weber. Because the collapsing core is far from equilibrium, the effects of general relativity are small.