Chaos in elliptical galaxies

TL;DR

This paper reviews the presence of chaos in elliptical galaxies, discusses the challenges in modeling such chaos, and demonstrates that stable, self-consistent models with high fractions of chaotic orbits are feasible.

Contribution

It challenges the notion that chaotic orbits hinder stable galaxy models and shows that current modeling methods can produce stable, chaotic-rich elliptical galaxy models.

Findings

High fractions of chaotic orbits are present in elliptical galaxy models.

Stable models with significant chaotic orbits can be constructed.

Schwarzschild's method has limitations but can be improved for such models.

Abstract

Here I present a review of the work done on the presence and effects of chaos in elliptical galaxies plus some recent results we obtained on this subject. The fact that important fractions of the orbits that arise in potentials adequate to represent elliptical galaxies are chaotic is nowadays undeniable. Alternatively, it has been difficult to build selfconsistent models of elliptical galaxies that include significant fractions of chaotic orbits and, at the same time, are stable. That is specially true for cuspy models of elliptical galaxies which seem to best represent real galaxies. I argue here that there is no physical impediment to build such models and that the difficulty lies in the method of Schwarzschild, widely used to obtain such models. Actually, I show that there is no problem in obtaining selfconsistent models of elliptical galaxies, even cuspy ones, that contain very high fractions of chaotic orbits and are, nevertheless, highly stable over time intervals of the order of a Hubble time.