Abstract

The radial transport of angular momentum is a central quantity in astrophysics, as it is an essential ingredient in the dynamics of many objects, among which the best known are accretion discs or radiative stars. In both cases, the mechanism that generates the turbulence and the amount of angular momentum transported outward remain to be clearly identified. Because it is deeply related to the generation of magnetic fields, understanding angular momentum transport is essential to dynamo theory.   In this talk, I will first describe a new laboratory experiment aiming to reproduce a black hole or proto-star accretion disk in the laboratory. In this experiment, a Couette flow is driven by an electromagnetic force rather than by the rotation of the boundaries. When the electromagnetic force applied to the liquid metal is large enough, it provides a configuration analogous to astrophysical disks, characterized by a fully turbulent flow that exhibits Keplerian rotation rates. The angular momentum is then transported through a non-dissipative regime, yielding predictions for the accretion rates of astrophysical disks.   In a second part, I will describe global numerical simulations aiming to model a radiative stellar layer. For some parameters, we report the existence of a subcritical transition to turbulence due to the generation of a dynamo magnetic field, very similar to the Tayler-Spruit model. This regime significantly enhances turbulent transport in radiative zones, leading to a drastic spin-down of the inner part of the star.   Bibliography: Vernet, Fauve, Gissinger, Phys. Rev. Lett. (2022) Petitdemange, Marcotte, Gissinger, Science (in revision, 2022)