Orbital alignment and mass segregation in galactic nuclei via vector resonant relaxation

TL;DR

This paper investigates how vector resonant relaxation causes massive stars in galactic nuclei to align their orbits into a thin disk, revealing insights into the distribution of black holes and stellar dynamics.

Contribution

It introduces a maximum entropy method to predict the long-term orbital orientation distribution of stars in galactic nuclei, accounting for various initial conditions.

Findings

Massive stars form a thin, self-aligned disk.

Disk thickness depends on initial mass function and cluster geometry.

Method offers a new way to infer intermediate mass black hole distribution.

Abstract

Supermassive black holes dominate the gravitational potential in galactic nuclei. In these dense environments, stars follow nearly Keplerian orbits and see their orbital planes relax through the potential fluctuations generated by the stellar cluster itself. For typical astrophysical galactic nuclei, the most likely outcome of this vector resonant relaxation (VRR) is that the orbital planes of the most massive stars spontaneously self-align within a narrow disc. We present a maximum entropy method to systematically determine this long-term distribution of orientations and use it for a wide range of stellar orbital parameters and initial conditions. The heaviest stellar objects are found to live within a thin equatorial disk. The thickness of this disk depends on the stars' initial mass function, and on the geometry of the initial cluster. This work highlights a possible (indirect) novel method to constrain the distribution of intermediate mass black holes in galactic nuclei.