Filling The Pockets: The Spherical Nature of 3D Deflagration in Thermonuclear Supernovae

TL;DR

This paper examines the three-dimensional hydrodynamics of thermonuclear supernovae, revealing that turbulence and magnetic fields significantly influence the burning process and improve the match with spherical models.

Contribution

It demonstrates that including turbulence and magnetic fields in 3D simulations enhances burning efficiency, addressing a key inconsistency in supernova explosion models.

Findings

Turbulence and magnetic fields promote mixing of burned and unburned material.

Enhanced mixing leads to more efficient burning and better spherical model agreement.

Magnetic and turbulent effects are most effective at small scales.

Abstract

We investigate thermonuclear explosions within the delayed detonation framework. While spherical delayed detonation models generally reproduce key observational features, a fundamental inconsistency emerges in three dimensions: 3D hydrodynamic simulations exhibit insufficient white dwarf expansion during the deflagration phase. We identify the early deflagration stage, when the burning is dominated by the laminar speed, as a critical phase and explore potential solutions using three dimensional magnetohydrodynamic simulations performed with the FLASH code. In hydrodynamical simulations, the early deflagration phase produces large pockets of unburned C/O, leading to inefficient burning. Much of the released energy is deposited into buoyantly rising plumes rather than into the global pre-expansion of the white dwarf, which is required to produce the partially burned layers characteristic of SNe Ia. In contrast, when preexisting turbulent velocity fields and strong magnetic fields, on scales expected from the smoldering phase, are included, the effective burning approaches that in spherical models. Both turbulence and magnetic fields promote the entrainment of burned material into unburned pockets, addressing a long-standing problem in multi-dimensional deflagration models. The resulting streaks of burned material enable the conductive ignition of the surrounding unburned fuel. The dominant effect is not a change in the small-scale flame physics (~10^{-3} cm), but rather enhanced mixing between burned and unburned material. As expected, this mechanism is most efficient when the turbulent length scales are smaller than those of the unburned plumes.