Multidimensional Simulations of the Accretion‐induced Collapse of White Dwarfs to Neutron Stars

We present 2.5D radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from 2D rotational equilibrium configurations. Electron capture leads to the collapse to nuclear densities of these cores within a few tens of milliseconds. The shock generated at bounce moves slowly, but steadily, outwards. Within 50-100ms, the stalled shock breaks out of the white dwarf along the poles. The blast is followed by a neutrino-driven wind that develops within the white dwarf, in a cone of ~40deg opening angle about the poles, with a Mdot of 5-8 x 10⁻³ Msun/s. The ejecta have an entropy on the order of 20-50 k_B/baryon, and an electron fraction distribution that is bimodal. By the end of the simulations, at >600ms after bounce, the explosion energy has reached 3-4 x 10^49 erg and the outflowing mass has reached a few times 0.001Msun. We estimate the asymptotic explosion energies to be lower than 10^50 ergs, significantly lower than those inferred in the core collapse of massive progenitors. AIC of WDs thus represents one instance where a neutrino mechanism leads undoubtedly to a successful, albeit weak, explosion. We document in detail the numerous effects of the fast rotation of the progenitors: the neutron stars are aspherical; the ``\ν\μ'' and \\ν̄_e luminosities are reduced compared to the \ν_e luminosity; the deleptonized region has a butterfly shape; the neutrino flux and electron fraction depend strongly upon latitude (a la von Zeipel); and a quasi-Keplerian 0.1-0.5Msun accretion disk is formed [abridged].