## M 1 Astronomy Internship 2021

### Distribution of stellar orbital orientations in galactic nuclei

**Astrophysical Context**

In the vicinity of a supermassive black hole, stars move on nearly Keplerian orbits. Yet, because of the enclosed stellar mass and relativistic corrections, the potential slightly deviates from the Keplerian one, which causes the stellar orbits to precess. Similarly, as a result of the finite number of stars, the mutual gravitational torques between pairs of stars also drive a rapid reshuffling of the stars' orbital orientations, much faster than the standard deflections by close encounters. Overall, the combination of these two effects leads to a stochastic evolution of stellar orbital angular momentum vectors, through a process named *resonant relaxation*.

**Upshot**

This internship will be focused on the process of *vector resonant relaxation*, namely the relaxation of stars' orbital orientations.
We will aim at deriving efficiently the long-term thermodynamical equilibria of such a dynamics.
We will explore in particular how fast multipole expansions can be tailored to that setup to allow for very efficient numerical explorations of these long-term relaxations.
These investigations should offer new clues on the spontaneous formation of non-sherical disc structures (possibly made of intermediary mass black holes) in galactic nuclei.

**Requirement**

Strong interest in theoretical astronomy, dynamics, analytical and numerical work.

**Framework**

The internship will be co-supervised by Jean-Baptiste Fouvry (IAP, Paris), Christophe Pichon (IAP, Paris), and Pierre-Henri Chavanis (LPT, Toulouse), as part of the SEGAL ANR (www.secular-evolution.org).

**References**

Rauch, K., Tremaine, S., 1996, 9603018

Kocsis, B., Tremaine, S., 2015, 1406.1178

Roupas, Z., Kocsis, B., Tremaine, S., 2017, 1701.03271

Takacs, A., Kocsis, B., 2018, 1712.04449

Szolgyen, A., Kocsis, B., 2018, 1803.07090

Fouvry, J.-B., Bar-Or, B., Chavanis, P.-H., 2019, 1812.07053