Gravitational collapse of white dwarfs to neutron stars: From initial conditions to explosions with neutrino-radiation hydrodynamics simulations

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Abstract Using general relativistic neutrino-radiation hydrodynamics simulations with the multi-group M1 scheme in one dimension, we investigate the collapse of massive, fully convective, and non-rotating white dwarfs (WDs), which are formed by accretion-induced collapse or merger-induced collapse, and the subsequent explosion. We produce initial WDs in hydrostatic equilibrium, which have super-Chandrasekhar mass and are about to collapse. The WDs have masses of $1.6\, M_{\odot }$ with different initial central densities specifically at $1.0\times 10^{10}$, $4.0\times 10^{9}$, $2.0\times 10^{9}$, and $1.0\times 10^{9}\:\mbox{g}\:\mbox{cm}^{-3}$. First, we examine the stability of initial WD in case weak interactions are turned off. Secondly, we calculate the collapse of WDs with weak interactions. We employ hydrodynamics simulations with Newtonian gravity in the first and second steps. Thirdly, we calculate the formation of neutron stars and accompanying explosions with general relativistic simulations. As a result, WDs with the highest density of $10^{10}\:\mbox{g}\:\mbox{cm}^{-3}$ collapse not by weak interactions but by the photodissociation of the iron, and three WDs with low central densities collapse by the electron capture as expected at the second step and succeed in the explosion with a small explosion energy of $\sim\! 10^{48}\:$erg at the third step. By changing the surrounding environment of WDs, we find that there is a minimum value of ejecta masses, which is $\sim\! 10^{-5}\, M_{\odot }$. With the most elaborate simulations of this kind so far, this value is one to two orders of magnitude smaller than previously reported values and is compatible with the estimated ejecta mass from FRB 121102.