Linking 1D Evolutionary to 3D Hydrodynamical Simulations of Massive Stars

TL;DR

This paper investigates convective boundary mixing in massive stars by linking 1D evolutionary models with 3D hydrodynamical simulations, revealing differences in boundary 'stiffness' that affect stellar evolution and explosive phenomena.

Contribution

It introduces a method to connect 1D stellar evolution models with 3D hydrodynamic simulations, focusing on convective boundary 'stiffness' and its impact on mixing processes.

Findings

Lower convective boundaries are 'stiffer' than upper boundaries.

Results agree with previous 3D hydrodynamic simulations.

Implications for stellar evolution and explosive phenomena.

Abstract

Stellar evolution models of massive stars are important for many areas of astrophysics, for example nucleosynthesis yields, supernova progenitor models and understanding physics under extreme conditions. Turbulence occurs in stars primarily due to nuclear burning at different mass coordinates within the star. The understanding and correct treatment of turbulence and turbulent mixing at convective boundaries in stellar models has been studied for decades but still lacks a definitive solution. This paper presents initial results of a study on convective boundary mixing (CBM) in massive stars. The 'stiffness' of a convective boundary can be quantified using the bulk Richardson number ($\textrm{Ri}_B$), the ratio of the potential energy for restoration of the boundary to the kinetic energy of turbulent eddies. A 'stiff' boundary ($\textrm{Ri}_B \sim 10^4$) will suppress CBM, whereas in the opposite case a 'soft' boundary ($\textrm{Ri}_B \sim 10$) will be more susceptible to CBM. One of the key results obtained so far is that lower convective boundaries (closer to the centre) of nuclear burning shells are 'stiffer' than the corresponding upper boundaries, implying limited CBM at lower shell boundaries. This is in agreement with 3D hydrodynamic simulations carried out by Meakin and Arnett [The Astrophysical Journal 667:448-475, 2007]. This result also has implications for new CBM prescriptions in massive stars as well as for nuclear burning flame front propagation in Super-Asymptotic Giant Branch stars and also the onset of novae.