« Kinetic theory in galactic centers » 
Christophe Pichon 
I will review the formalism allowing for the description of the longterm evolution of a large set of particles orbiting a dominant massive object, such as in galactic nuclei. Because stars move in the quasiKeplerian potential induced by the central black hole, their orbits can be approximated by ellipses whose orientations remain fixed over many dynamical times. Yet, on secular timescales, such a system will undergo a slow collisional relaxation driven by the remaining fluctuations in the system. When these fluctuations originate from the system intrinsic graininess (finiteN effects), the associated (scalar) resonant relaxation is captured by the (degenerate) inhomogeneous BalescuLenard equation. I will review in detail this kinetic formalism and emphasise the key physical mechanisms at play in this context. I will show in particular how one can account for the system's inhomogeneity (intricate trajectories), as well as the system's ability to amplify perturbations (selfgravity). I will finally show how such methods may be used to study the selfinduced resonant relaxation of a discrete selfgravitating razorthin axisymmetric disc orbiting a massive black hole, to recover for example the quenching of resonant diffusion in the vicinity of the black hole due to the divergence of the relativistic precessions.

vendredi 2 février 2018  11:00 Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris 
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