Orbit classification of low and high angular momentum stars

TL;DR

This study analyzes how angular momentum influences star orbit types in a disk galaxy model, revealing that low angular momentum stars tend to have chaotic orbits, while high angular momentum stars mostly follow regular paths.

Contribution

It introduces a comprehensive method combining SALI and spectral dynamics to classify star orbits based on angular momentum in an axisymmetric galaxy model.

Findings

Low angular momentum stars are more likely to have chaotic orbits.

High angular momentum stars predominantly follow regular orbits.

The percentage of chaotic orbits decreases as angular momentum increases.

Abstract

We determine the character of orbits of stars moving in the meridional plane $(R,z)$ of an axially symmetric time-independent disk galaxy model with a spherical central nucleus. In particular, we try to reveal the influence of the value of the angular momentum on the different families of orbits of stars, by monitoring how the percentage of chaotic orbits, as well as the percentages of orbits of the main regular resonant families evolve when angular momentum varies. The smaller alignment index (SALI) was computed by numerically integrating the equations of motion as well as the variational equations to extensive samples of orbits in order to distinguish safely between ordered and chaotic motion. In addition, a method based on the concept of spectral dynamics that utilizes the Fourier transform of the time series of each coordinate is used to identify the various families of regular orbits and also to recognize the secondary resonances that bifurcate from them. Our investigation takes place both in the physical $(R,z)$ and the phase $(R,\dot{R})$ space for a better understanding of the orbital properties of the system. Our numerical computations reveal that low angular momentum stars are most likely to move in chaotic orbits, while on the other hand, the vast majority of high angular momentum stars perform regular orbits.