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Session 88 - Structure and Kinematics of Galaxies.
Oral session, Wednesday, January 17
La Condesa, Hilton
HST observations of elliptical galaxies have revealed the presence of strong cusps or black holes at their centers. We investigate the development of chaos in triaxial elliptical galaxies arising from the presence of central concentrations. The chief influence of a cusp or black hole is the disruption of the regular box orbits which are believed to form the ``backbone'' of integrable triaxial models. The Liapunov characteristic numbers for a large number of stochastic orbits tend to converge to a single value after a long time (\sim 10^4 orbital times). The Liapunov times (which measure the time scales for divergence of two nearby orbits) are typically 3-5 crossing times. This confirms the conventional wisdom that all stochastic regions of phase space are connected and that slow diffusion occurs between the different regions. Large ensembles of stochastic orbits chosen to have identical energies, mix on timescales of less than \sim 100 orbital times and reach a near-invarient density distribution. These results suggest that the stochastic regions of phase space in most ellipticals are likely to be fully mixed, which strongly constrains the existance of self-consistent triaxial equilibria.
