Hydrodynamic instability in eccentric Keplerian discs

Astronomy Unit Seminars
Dr Adrian Barker (DAMTP, Cambridge)
Sijme-Jan Paardekooper
October 31st, 2014 at 14:30
GO Jones Room 610

Eccentric gas discs are thought to arise in a number of astrophysical contexts, including certain classes of binary stars and probably also in protoplanetary discs. The eccentricity evolution of newly born planets due to their tidal interaction with the disc is intricately coupled with the evolution of eccentric motions within the disc. However, to determine the outcome of such processes requires understanding the dynamics of eccentric discs. I will describe recent work to understand the dynamics and stability of eccentric discs. In particular, I will describe the construction of a local model of an eccentric disc, similar to the shearing box. This is used to study the vertical oscillatory flows produced due by the variation of the vertical gravitational acceleration around an eccentric orbit, as well as their stability to locally axisymmetric perturbations. Eccentric discs are found to be generically unstable to a parametric instability involving the excitation of small-scale inertial waves. The nonlinear evolution of these instabilities is found to generate hydrodynamic activity in the disc, and may limit the eccentricities that can be achieved in practice. Throughout this talk, I will highlight the importance of considering three-dimensional models of eccentric discs in order to correctly capture their evolution.