Asymptotic gravity waves in core-collapse progenitor stars

Internal gravity waves (IGW) are generically excited at convective boundaries inside stars. During the final months before a massive stars’ core-collapse, the excited IGW carry energy and angular momentum so large that the wave transport can e.g. completely set the rotation period of the neutron star remnant. In this talk, I present the first three-dimensional simulation of a core-collapse progenitor with which we can characterise IGW generation and transport preceding core-collapse. First I will show that the energy carried by convectively generated IGW in our simulation is described remarkably well by the established asymptotic theory, which utilizes e.g. the WKB approximation. But, the IGW’s subsequent propagation and dissipation depends very sensitively on the rotation. And in 3D, the equilibrium rotation patterns that develop are too complex to be captured in the established asymptotic theory for wave transport. I will present the rich nonlinear wave dynamics in our 3D simulation responsible for angular momentum transport and wave dissipation. I will propose that the angular momentum transport is governed by a “mean flow” interaction between global rotation and IGW transport. Mean flow interactions can explain the periodic Easterly <-> Westerly sudden reversal of winds at the equator on Earth, Saturn and Jupiter. If such reversals are realised in massive stars, it has implications for several exotic phenomena. This includes IGW driven mass loss outbursts observed in the final months before core-collapse supernova, and also gamma ray burst progenitor stars - which require very extreme rotation at core collapse.