Three-Dimensional Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae

TL;DR

This paper presents 3D hydrodynamical simulations of the standing accretion shock instability (SASI) in core-collapse supernovae, revealing mode behaviors, nonlinear couplings, and spectral properties in a realistic post-bounce environment.

Contribution

It extends previous axisymmetric studies to fully 3D simulations, analyzing mode interactions, nonlinear saturation, and spectral characteristics of SASI in supernova conditions.

Findings

Growth rates of SASI are degenerate across azimuthal modes.

Nonlinear mode couplings produce m=0 and m≠0 modes depending on initial perturbations.

3D models show lower saturation levels and more complex turbulence than 2D models.

Abstract

We have studied non-axisymmetric standing accretion shock instability, or SASI, by 3D hydrodynamical simulations. This is an extention of our previous study on axisymmetric SASI. We have prepared a spherically symmetric and steady accretion flow through a standing shock wave onto a proto-neutron star, taking into account a realistic equation of state and neutrino heating and cooling. This unperturbed model is supposed to represent approximately the typical post-bounce phase of core-collapse supernovae. We then have added a small perturbation (~1%) to the radial velocity and computed the ensuing evolutions. Not only axisymmetric but non-axisymmetric perturbations have been also imposed. We have applied mode analysis to the non-spherical deformation of the shock surface, using the spherical harmonics. We have found that (1) the growth rates of SASI are degenerate with respect to the azimuthal index m of the spherical harmonics Y_l^m, just as expected for a spherically symmetric background, (2) nonlinear mode couplings produce only m=0 modes for the axisymmetric perturbations, whereas m=!0 modes are also generated in the non-axisymmetric cases according to the selection rule for the quadratic couplings, (3) the nonlinear saturation level of each mode is lower in general for 3D than for 2D because a larger number of modes are contributing to turbulence in 3D, (4) low l modes are dominant in the nonlinear phase, (5) the equi-partition is nearly established among different m modes in the nonlinear phase, (6) the spectra with respect to l obey power laws with a slope slightly steeper for 3D, and (7) although these features are common to the models with and without a shock revival at the end of simulation, the dominance of low l modes is more remarkable in the models with a shock revival.