Multi‐Dimensional Simulations of the Accretion‐Induced Collapse of White Dwarfs to Neutron Stars

Abstract

We have performed 2.5D radiation‐hydrodynamics simulations of the accretion‐induced collapse (AIC) of white dwarfs, starting from 2D rotational equilibrium configurations of a 1.92‐M⊙ model. Electron capture leads to the collapse to nuclear densities of the core within a few tens of milliseconds. The shock generated at bounce moves slowly, but steadily, outwards. Within 50–100 ms, 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 ∼ 40° opening angle about the poles, with a mass loss rate of 5 × 10−3M⊙yr−1. The ejecta have an entropy on the order of 20–50 kB/baryon, and an electron fraction distribution that is bimodal. By the end of the simulations, at ⩾600 ms after bounce, the explosion energy has reached 3 × 1049 erg and the total ejecta mass has reached a few times 0.001 M⊙. We estimate the asymptotic explosion energies to be slightly lower than 1050 erg, significantly lower than those inferred for standard core collapse. The AIC of white dwarfs thus represents one instance where a neutrino mechanism leads undoubtedly to a successful, albeit weak, explosion.We summarize the numerous effects of the fast rotation of the progenitor: The neutron star is aspherical; the “νμ” and ν̄e neutrino luminosities are reduced compared to the νe neutrino luminosity; the deleptonized region has a “butterfly” shape; the neutrino flux and electron fraction depend strongly upon latitude (à la von Zeipel); and a quasi‐Keplerian 0.5‐M⊙ accretion disk is formed.