Escape dynamics in a binary system of interacting galaxies

TL;DR

This study investigates how stars escape from a binary galaxy system using numerical methods, revealing energy-dependent escape patterns, fractal basin boundaries, and the influence of Lagrangian points on escape routes.

Contribution

It provides a detailed numerical analysis of escape dynamics in a binary galaxy model, highlighting the role of energy levels and fractal basin boundaries in escape behavior.

Findings

Escape rates are higher near the critical escape energy.

Escape basin boundaries are fractal in nature.

Most orbits escape quickly at high energies.

Abstract

The escape dynamics in an analytical gravitational model which describes the motion of stars in a binary system of interacting dwarf spheroidal galaxies is investigated in detail. We conduct a numerical analysis distinguishing between regular and chaotic orbits as well as between trapped and escaping orbits, considering only unbounded motion for several energy levels. In order to distinguish safely and with certainty between ordered and chaotic motion, we apply the Smaller ALingment Index (SALI) method. It is of particular interest to locate the escape basins through the openings around the collinear Lagrangian points $L_1$ and $L_2$ and relate them with the corresponding spatial distribution of the escape times of the orbits. Our exploration takes place both in the configuration $(x,y)$ and in the phase $(x,\dot{x})$ space in order to elucidate the escape process as well as the overall orbital properties of the galactic system. Our numerical analysis reveals the strong dependence of the properties of the considered escape basins with the total orbital energy, with a remarkable presence of fractal basin boundaries along all the escape regimes. It was also observed, that for energy levels close to the critical escape energy the escape rates of orbits are large, while for much higher values of energy most of the orbits have low escape periods or they escape immediately to infinity. We hope our outcomes to be useful for a further understanding of the escape mechanism in binary galaxy models.