How does the mass transport in disk galaxy models influence the character of orbits?

TL;DR

This study investigates how mass transport from the disk to the nucleus in a galaxy model affects stellar orbit regularity and chaos, revealing increased chaos with a more massive nucleus and orbit character changes during evolution.

Contribution

It introduces a dynamic galaxy model with mass transfer and analyzes its impact on orbit regularity and chaos, using advanced numerical methods.

Findings

Chaos increases as the nucleus becomes more massive.

Some orbits switch between regular and chaotic states during evolution.

Certain orbit families remain stable despite galaxy development.

Abstract

We explore the regular or chaotic nature of orbits of stars moving in the meridional (R,z) plane of an axially symmetric time-dependent disk galaxy model with a central, spherically symmetric nucleus. In particular, mass is linearly transported from the disk to the galactic nucleus, in order to mimic, in a way, the case of self-consistent interactions of an actual N-body simulation. We thus try to unveil the influence of this mass transportation 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 as the galaxy develops a dense and massive nucleus in its core. The SALI method is applied to samples of orbits in order to distinguish safely between ordered and chaotic motion. In addition, a method based on the concept of spectral dynamics is used for identifying the various families of regular orbits and also for recognizing the secondary resonances that bifurcate from them. Our computations strongly suggest that the amount of the observed chaos is substantially increased as the nucleus becomes more massive. Furthermore, extensive numerical calculations indicate that there are orbits which change their nature from regular to chaotic and vice versa and also orbits which maintain their orbital character during the galactic evolution. The present outcomes are compared to earlier related work.