The Convective Urca Process with Implicit Two‐dimensional Hydrodynamics

Consideration of the role of the convective flux in the thermodymics of theconvective Urca neutrino loss process in degenerate, convective, quasi-static,carbon-burning cores shows that the convective Urca process slows down theconvective current around the Urca-shell, but, unlike the "thermal" Urcaprocess, does not reduce the entropy or temperature for a given convectivevolume. Here we demonstrate these effects with two-dimensional numericalhydrodynamical calculations. These two-dimensional implicit hydrodynamicscalculations invoke an artificial speeding up of the nuclear and weak rates.They should thus be regarded as indicative, but still qualitative. We findthat, compared to a case with no Urca-active nuclei, the case with Urca effectsleads to a higher entropy in the convective core because the energy released bynuclear burning is confined to a smaller volume by the effective boundary atthe Urca shell. All else being equal, this will tend to accelerate theprogression to dynamical runaway. We discuss the open issues regarding theimpact of the convective Urca process on the evolution to the "smolderingphase" and then to dynamical runaway.Comment: 22 pages, 11 figures, accepted for publication in the Astrophysical Journa