Hydrodynamic simulations of shell convection in stellar cores

TL;DR

This paper uses hydrodynamic simulations to study shell convection in various stellar cores, revealing that entropy barriers are less influential than previously thought and identifying a new mixing process.

Contribution

It introduces detailed hydrodynamic simulations of shell convection in different stellar core scenarios, challenging existing assumptions about entropy barriers.

Findings

Entropy barriers are less significant for stellar structure than previously believed.

A new dynamic mixing process operating below shell convection zones was discovered.

Simulations cover helium, carbon, and oxygen burning shells in various star types.

Abstract

Shell convection driven by nuclear burning in a stellar core is a common hydrodynamic event in the evolution of many types of stars. We encounter and simulate this convection (i) in the helium core of a low-mass red giant during core helium flash leading to a dredge-down of protons across an entropy barrier, (ii) in a carbon-oxygen core of an intermediate-mass star during core carbon flash, and (iii) in the oxygen and carbon burning shell above the silicon-sulfur rich core of a massive star prior to supernova explosion. Our results, which were obtained with the hydrodynamics code HERAKLES, suggest that both entropy gradients and entropy barriers are less important for stellar structure than commonly assumed. Our simulations further reveal a new dynamic mixing process operating below the base of shell convection zones.