The S stars' zone of avoidance in the Galactic center

TL;DR

This study models the origin and orbital evolution of S stars in the Galactic center, explaining the observed 'zone of avoidance' through binary disruption and relaxation processes.

Contribution

It introduces a comprehensive model combining binary disruption and orbital relaxation to explain S-star distributions and the zone of avoidance.

Findings

Binary disruption near the black hole explains the S-star distribution.

Orbital relaxation accounts for the eccentricity distribution of S stars.

The model reproduces the observed zone of avoidance in S-star orbits.

Abstract

This paper investigates the origin and orbital evolution of S stars in the Galactic center using models of binary disruption and relaxation processes. We focus on explaining the recently discovered ``zone of avoidance'' in S-star orbital parameters, defined as a region where no S stars are observed with pericenters of $\log(r_p / {\rm AU}) \leq 1.57 + 2.6(1 - e)$ pc. We demonstrate that the observed S-star orbital distributions, including this zone of avoidance and their thermal eccentricity distribution, can be largely explained by the continuous disruption of binaries near the central supermassive black hole, followed by orbital relaxation. Our models consider binaries originating from large scales ($5$--$100$ pc) and incorporate empirical distributions of binary properties. We simulate close encounters between binaries and the black hole, tracking the remnant stars' orbits. The initially highly eccentric orbits of disrupted binary remnants evolve due to nonresonant and resonant relaxation in the Galactic center potential. While our results provide insights into the formation mechanism of S stars, there are limitations, such as uncertainties in the initial binary population and mass function and simplifications in our relaxation models. Despite these caveats, our study demonstrates the power of using S-star distributions to probe the dynamical history and environment of the central parsec of our Galaxy.