Dynamics of Cuspy Triaxial Galaxies with a Supermassive

This talk provides a progress report on an extended collaboration which has aimed to address two basic questions, namely: Should one expect to see cuspy, triaxial galaxies in nature? And can one construct realistic cuspy, triaxial equilibrium models that are robust? Three technical results are described: (1) Unperturbed chaotic orbits in cuspy triaxial potentials can be extraordinarily sticky, much more so than orbits in many other three-dimensional potentials. (2) Even very weak perturbations can be important by drastically reducing, albeit not completely eliminating, this stickiness. (3) A simple toy model facilitates a simple understanding of why black holes and cusps can serve as an effective source of chaos. These results suggest that, when constructing models of galaxies using Schwarzschild’s method or any analogue thereof, astronomers would be well advised to use orbital building blocks that have been perturbed by ‘noise’ or other weak irregularities, since such building blocks are likely to be more nearly time-independent than orbits evolved in the absence of all perturbations. 1. Unperturbed chaotic orbits tend to be extremely sticky The results reported here derive from a numerical analysis of orbits in the triaxial Dehnen potentials, where (cf. Merritt & Fridman 1996)