Complex Instability Around the Rotation Axis of Stellar Systems. Part 1. Galactic Potentials

摘要

The frequent instability of the radial periodic orbits along the rotation axis of bulges, spheroids, and other rotating triaxial ellipsoids is numerically investigated in realistic gravitational potentials. Especially in nearly axisymmetric systems, complex instability sets in as soon as rotation takes place. The classical sequence of bifurcation stable goes to semi-unstable goes to unstable found by Heissler et al. (1982) evolves to the sequence stable goes to semi-unstable goes to stable goes to complex unstable, and finally to the sequence stable goes to complex unstable when the figure rotation is increased. Addition of a concentrated mass in the core modifies this behavior in the sense that the maximum orbital amplitude at which the bifurcation stable goes to complex unstable occurs is lowered. The diffusion time of chaotic orbits, starting along the rotation axis rapidly becomes shorter than the Hubble time when the central mass makes all the z-axis orbits complex unstable.