Secular theory of the orbital evolution of the young stellar disc in the Galactic Centre

TL;DR

This paper develops a secular theory for the orbital evolution of young stars in the Galactic Centre, considering mutual interactions and external perturbations, revealing two distinct dynamical modes that influence the stellar disc's evolution.

Contribution

It introduces semi-analytic formulas for orbit evolution under combined mutual and external perturbations, highlighting two qualitative dynamical modes.

Findings

Strongly interacting orbits become synchronized and precess together.

Weaker interactions cause independent precession and inclination oscillations.

The processes may explain the evolution of the young stellar disc near the Milky Way's black hole.

Abstract

We investigate the orbital evolution of a system of N mutually interacting stars on initially circular orbits around the dominating central mass. We include perturbative influence of a distant axisymmetric source and an extended spherical potential. In particular, we focus on the case when the secular evolution of orbital eccentricities is suppressed by the spherical perturbation. By means of standard perturbation methods, we derive semi-analytic formulae for the evolution of normal vectors of the individual orbits. We find its two qualitatively different modes. Either the orbits interact strongly and, under such circumstances, they become dynamically coupled, precessing synchronously in the potential of the axisymmetric perturbation. Or, if their mutual interaction is weaker, the orbits precess independently, interchanging periodically their angular momentum, which leads to oscillations of inclinations. We argue that these processes may have been fundamental for the evolution of the disc of young stars orbiting the supermassive black hole in the centre of the Milky Way.