Angular momentum transport in electrically-conducting fluids

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• Dr. Cristophe Gissinger - ENS Paris
• Monday 18 October 2021, 14:00-15:00
• Online.

If you have a question about this talk, please contact Callum William Fairbairn.

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.

In this talk, I will first describe a new laboratory experiment in which 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, the experiment 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 transport in radiative zones, leading to a drastic spin-down of the inner part of the star.

This talk is part of the DAMTP Astrophysics Seminars series.

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