Stability and convergence of nuclear detonations in white dwarf collisions

TL;DR

This study examines the numerical stability and convergence of thermonuclear detonations in white dwarf collisions, establishing resolution and parameter bounds for accurate simulation of nuclear products and energy release.

Contribution

It introduces specialized geometric gridding and mesh strategies for simulating white dwarf collisions and defines parameter bounds for stable, convergent detonation modeling.

Findings

Grid resolutions of 5 km or better are needed for <10% uncertainty in energy and products.

Limiter parameters significantly affect the stability and convergence of detonation simulations.

Results are applicable across various white dwarf compositions and collision scenarios.

Abstract

We investigate the numerical stability of thermonuclear detonations in 1D accelerated reactive shocks and 2D binary collisions of equal mass, magnetized and unmagnetized white dwarf stars. To achieve high resolution at initiation sites, we devised geometric gridding and mesh velocity strategies specially adapted to the unique requirements of head-on collisional geometries, scenarios in which one expects maximum production of iron-group products. We study effects of grid resolution and the limiting of temperature, energy generation, and reactants for different stellar masses, separations, magnetic fields, initial compositions, detonation mechanisms, and limiter parameters across a range of cell sizes from 1 to 100 km. Our results set bounds on the parameter space of limiter amplitudes for which both temperature and energy limiting procedures yield consistent and monotonically convergent solutions. Within these bounds we find grid resolutions of 5 km or better are necessary for uncertainties in total released energy and iron-group products to drop below 10%. Intermediate mass products (e.g., calcium) exhibit similar convergence trends but with somewhat greater uncertainty. These conclusions apply equally to pure C/O WDs, multi-species compositions (including helium shells), magnetized and unmagnetized cores, and either single or multiple detonation scenarios.