Simulations of non-axisymmetric rotational core collapse

TL;DR

This paper presents the first 3D hydrodynamic simulations of non-axisymmetric instabilities in collapsing, rapidly rotating stellar cores, analyzing gravitational wave emission and the development of bar-like deformations.

Contribution

It introduces pioneering 3D simulations of non-axisymmetric instabilities during core collapse, revealing the growth of bar-like structures and their impact on gravitational radiation.

Findings

Secular instabilities do not develop within the simulated timeframe.

Dynamically unstable cores show strong nonlinear non-axisymmetric growth.

No significant gravitational wave enhancement despite tri-axial deformation.

Abstract

We report on the first three-dimensional hydrodynamic simulations of secular and dynamical non-axisymmetric instabilities in collapsing, rapidly rotating stellar cores which extend well beyond core bounce. The resulting gravitational radiation has been calculated using the quadrupole approximation. We find that secular instabilities do not occur during the simulated time interval of several 10 ms. Models which become dynamically unstable during core collapse show a strong nonlinear growth of non-axisymmetric instabilities. Both random and coherent large scale initial perturbations eventually give rise to a dominant bar-like deformation ($\exp(\pm im\phi$) with $m=2$). In spite of the pronounced tri-axial deformation of certain parts of the core no considerable enhancement of the gravitational radiation is found. This is due to the fact that rapidly rotating cores re-expand after core bounce on a dynamical time scale before non-axisymmetric instabilities enter the nonlinear regime. Hence, when the core becomes tri-axial, it is no longer very compact.