Disruptions of stars and binary systems on chaotic orbits in an axisymmetric Milky Way center

TL;DR

This study models the chaotic stellar orbits near the Milky Way's center, revealing that collisionless disruptions are more frequent than collisional ones, impacting phenomena like hypervelocity stars and tidal disruption events.

Contribution

It provides the first detailed analysis of collisionless disruption rates in the Milky Way's center using an observationally benchmarked model, highlighting the dominance of chaotic trajectories.

Findings

Collisionless disruption rates can exceed collisional rates by orders of magnitude.

Chaotic low z-angular momentum trajectories are common near the galactic center.

Disruption phenomena are biased towards shallow, high-inclination encounters, affecting debris distribution.

Abstract

Non-spherical potentials allow a wide range of trajectories, both regular and chaotic, whose periapse distances can vary orbit to orbit. In particular chaotic trajectories can bring a system arbitrarily close to the central massive black hole leading to a disruption. In this paper, we work with an observationally benchmarked model of the innermost 200 pc of the Milky Way and show that low z-angular momentum trajectories are commonly chaotic. We compute the timescales and properties of close pericenter passages, and compare the implied collisionless disruption rate to the well-studied collisional rate from 2-body scatterings. We find that the relative collisionless rate can dominate by orders of magnitude. Our calculations are relevant for a wide range of disruption phenomena, including the production of hypervelocity stars (HVSs) and tidal disruption events (TDEs). Most of these disruptions involve stars come from the Nuclear Stellar Cluster, with a pericenter distribution that strongly favours shallow encounters, and a preference for high inclination interactions. The latter implies that unbound disrupted material - whether ejected stars or stellar debris - would be preferentially directed towards the galactic poles. Many of our conclusions apply generally to any galaxy with a non-spherical galactic centre potential and central massive black hole.