Semi-Analytical Fokker Planck Models for Nuclear Star Clusters

TL;DR

This paper develops a semi-analytical model using Fokker-Planck equations to describe stellar dynamics in nuclear star clusters, improving estimates of inspiral rates and implications for galactic transients.

Contribution

It introduces a self-similar solution to the 2D Fokker-Planck equation for nuclear star clusters, capturing the transition between diffusion and advection regimes.

Findings

Provides density and flux profiles of stellar objects in clusters.

Enhances rate estimates for extreme mass-ratio inspirals.

Suggests implications for galactic center transient phenomena.

Abstract

We study the dynamics of nuclear star clusters, the dense stellar environments surrounding massive black holes in the centers of galaxies. We consider angular momentum diffusion due to two-body scatterings among stellar objects and energy advection due to gravitational wave emission upon interaction with the central massive black hole. Such dynamics is described by a two-dimensional Fokker-Planck equation in energy-angular momentum space. Focusing on the transition between the diffusion-dominated region and the advection-dominated one, we utilize self-similarity to obtain a full solution for the Fokker-Planck equation. This solution provides the density and flux of the stellar objects in nuclear star clusters. This improves the rate estimates for extreme mass-ratio inspirals, and has interesting implications for a new class of galactic center transients called quasi-periodic eruptions.