Core-collapse of white dwarfs with super Chandrasekhar mass
speaker: Masamitsu Mori
Abstract:
Recently, Fast Radio Bursts (FRBs) from globular clusters have been reported (Kirsten et al. 2022). A model has been proposed suggesting that young neutron stars (magnetars) may be involved in causing FRBs. However, these FRBs have been observed in globular clusters where star formation has ended. This implies the possibility that young magnetars were formed in the old stellar population.
As an explanation for this celestial phenomenon, it has been proposed that a white dwarf (WD) binary system merged and exceeded the Chandrasekhar mass limit, causing a collapse due to a decrease in degenerate pressure through electron capture reactions, leading to a gravitational collapse supernova explosion rather than a type Ia supernova explosion.
Therefore, we conducted a general relativistic neutrino radiation hydrodynamics calculation for a 1.6 solar mass WD and successfully achieved an explosion. In this simulation, we assumed hydrostatic equilibrium and used the Chandrasekhar mass before gravitational collapse as the initial conditions.
In this study, we used a one-dimensional simulation and performed calculations that implemented general relativistic gravity, a state equation based on nuclear physics, and a moment method for neutrino radiation transport. First, we confirmed stability under adiabatic conditions and then calculated the process leading to gravitational collapse through a decrease in the Chandrasekhar mass due to electron capture reactions by solving the neutrino radiation transport. Up to this point, we used Newtonian gravity to reduce numerical errors. Finally, we performed an explosion calculation with consideration of general relativistic gravity for the model that underwent gravitational collapse.
The explosion reproduced in this study was very small, with an explosion energy of $3 \times 10^{48}$ erg and an ejecta mass of $5 \times 10^{-4}~M_{\odot}$.