The thermodynamics of rotating black hole clusters

Yuri Levin

Center for Computational Astrophysics, Flariton Institute

Statistical physics has a bad track record in describing large-N gravitational systems.

It has become clear over the last several years that there is a remarkable exception

to this rule. Resonant relaxation due to orbit-averaged secular dynamics in galactic nuclei

drives them to states of thermal and rotational equilibria on an astronomically short timescale.

Statistical physics becomes a powerful, yet under-appreciated tool to study such systems.

I will introduce the general formalism (due mostly to Touma and Tremaine, but going as far back as Lynden-Bell), 

as well as a novel numerical algorithm for finding equilibria due to Andrei Gruzinov. 

There are fun applications: phase transitions leading to lopsided precessing equilibria (such as the nucleus of

Andromeda), and strong clustering in eccentricity and inclination of stellar-mass black holes.

I will use statistical physics to argue that secular-dynamical friction must exist and that moreover, it

plays a huge role in galactic nuclei, turning rotating clusters into 

flywheels that control the orbits of all heavy objects inside them, such as stellar discs and IMBHs.

I will speculate on its effect on the spin of the supermassive black hole itself.