The core helium flash revisited: II. Two and three-dimensional hydrodynamic simulations

TL;DR

This study uses advanced 2D and 3D hydrodynamic simulations to analyze turbulent convection during the core helium flash, revealing differences in flow patterns, velocities, and convection zone growth compared to traditional models.

Contribution

It provides the first detailed 3D hydrodynamic simulations of the core helium flash, showing better agreement with mixing length theory and highlighting turbulent entrainment effects.

Findings

3D models show less explosive behavior than 2D.

Convective velocities are smaller in 3D models.

Outer convection zone has a sub-adiabatic temperature gradient.

Abstract

We study turbulent convection during the core helium flash close to its peak by comparing the results of two and three-dimensional hydrodynamic simulations. We use a multidimensional Eulerian hydrodynamics code based on state-of-the-art numerical techniques to simulate the evolution of the helium core of a $1.25 M_{\odot}$ Pop I star. Our three-dimensional hydrodynamic simulations of the evolution of a star during the peak of the core helium flash do not show any explosive behavior. The convective flow patterns developing in the three-dimensional models are structurally different from those of the corresponding two-dimensional models, and the typical convective velocities are smaller than those found in their two-dimensional counterparts. Three-dimensional models also tend to agree better with the predictions of mixing length theory. Our hydrodynamic simulations show the presence of turbulent entrainment that results in a growth of the convection zone on a dynamic time scale. Contrary to mixing length theory, the outer part of the convection zone is characterized by a sub-adiabatic temperature gradient.