The Interplay between Proto–Neutron Star Convection and Neutrino Transport in Core‐Collapse Supernovae

Abstract

We couple two-dimensional hydrodynamics to realistic one-dimensional multigroup Ñux-limited di †u-sion neutrino transport to investigate protoÈneutron star convection in core-collapse supernovae, and more speciÐcally, the interplay between its development and neutrino transport. Our initial conditions, time-dependent boundary conditions, and neutrino distributions for computing neutrino heating, cooling, and deleptonization rates are obtained from one-dimensional simulations that implement multigroup Ñux-limited di †usion and one-dimensional hydrodynamics.The development and evolution of protoÈneutron star convection are investigated for both 15 and 25 models, representative of the two classes of stars with compact and extended iron cores, respectively. M _ For both models, in the absence of neutrino transport, the angle-averaged radial and angular convection velocities in the initial Ledoux unstable region below the shock after bounce achieve their peak values in D20 ms, after which they decrease as the convection in this region dissipates. The dissipation occurs as the gradients are smoothed out by convection. This initial protoÈneutron star convection episode seeds additional convectively unstable regions farther out beneath the shock. The additional protoÈneutron star convection is driven by successive negative entropy gradients that develop as the shock, in propagating out after core bounce, is successively strengthened and weakened by the oscillating inner core. The convection beneath the shock distorts its sphericity, but on the average the shock radius is not boosted signiÐcantly relative to its radius in our corresponding one-dimensional models.In the presence of neutrino transport, protoÈneutron star convection velocities are too small relative to bulk inÑow velocities to result in any signiÐcant convective transport of entropy and leptons. This is evident in our two-dimensional entropy snapshots, which in this case appear spherically symmetric. The peak angle-averaged radial and angular convection velocities are orders of magnitude smaller than they are in the corresponding "" hydrodynamics-only ÏÏ models.A simple analytical model supports our numerical results, indicating that the inclusion of neutrino transport reduces the entropy-driven (lepton-driven) convection growth rates and asymptotic velocities by a factor D3 (50) at the neutrinosphere and a factor D250 (1000) at o \ 1012 g cm~3, for both our 15 and 25 models. Moreover, when transport is included, the initial postbounce entropy gradient is M _ smoothed out by neutrino di †usion, whereas the initial lepton gradient is maintained by electron capture and neutrino escape near the neutrinosphere. Despite the maintenance of the lepton gradient, protoÈ neutron star convection does not develop over the 100 ms duration typical of all our simulations, except in the instance where "" low-test ÏÏ intial conditions are used, which are generated by core-collapse and bounce simulations that neglect neutrinoÈelectron scattering and ionÈion screening...

General Relativistic Effects in the Core Collapse Supernova Mechanism

“…This focus on convection was motivated in part by the potential of convection for increasing the likelihood of explosions, and in part by a number of observations of SN 1987A, which indicate that extensive mixing occurred throughout much of the ejected material, pointing, by inference, to Ñuid instabilities arising during the explosion itself. These investigations have employed multidimensional simulations with Newtonian hydrodynamics and transport (Herant, Benz, & Colgate, 1992 ;Herant et al 1994 ;Miller, Wilson, & Mayle 1993 ;Janka & 1995Burrows, Hayes, & Muller Fryxell, 1995 ;Mezzacappa et al 1998aMezzacappa et al , 1998b. While this work is extremely important, it has ignored the role of GR.…”

Simulations of stellar core collapse, bounce, and postbounce evolution with Boltzmann neutrino transport, and implications for the core collapse supernova mechanism

“…This will occur in intermediate regimes in which neutrino transport is efficient but in which the neutrinos are still strongly enough coupled to the matter. Figures 1 and 2 from Mezzacappa et al [7] demonstrate that this equilibration can in fact occur. Figure 1 shows the onset and development of proto-neutron star convection in a 25 M⊙ model shortly after bounce in a simulation that did not include neutrino transport, i.e., that was a hydrodynamics-only run.…”

“…Therefore, the question arises whether or not failures to produce explosions in past one-dimensional models were the result of the transport approximations employed. It is important to note that, without invoking protoneutron star (e.g., neutron finger) convection, simulations that implement multigroup flux-limited diffusion do not produce explosions [23,13] (as we will discuss, the existence and vigor of proto-neutron star convection is a matter of debate [7,14,16]). …”

“…The heating is mediated primarily by the absorption of electron neutrinos and antineutrinos on the dissociation-liberated nucleons behind the shock. This past decade has also seen the emergence of multidimensional supernova models, which have investigated the role convection, rotation, and magnetic fields may play in the explosion [4][5][6][7][8][9][10], in some cases invoking new explosion paradigms.…”

Supernova neutrino challenges

“…For neutrino transport, it indicates one of two approaches: multidimensional diffusion in regions with strong radiation/fluid coupling, matched with a spherically symmetric 'light bulb' approximation in weakly coupled regions ("thick/thin"); or the (mostly) independent application of a spherically symmetric formalism/algorithm to separate spatial angle bins ("ray-by-ray"). disputed [18,39,40]; and though related phenomena may operate [40], more recent simulations with energy-dependent neutrino transport and true two-dimensional fluid dynamics indicate that fluid motions are either suppressed by neutrino transport [19] or have little effect on neutrino luminosities and supernova dynamics [36,38].…”