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Session 13 - Galaxies & Globular Clusters.
Oral session, Monday, June 09
North Main Hall F/G,
The motion of stars in triaxial stellar systems with central density cusps, \rho\propto r^-\gamma, or central singularities ("black holes"), is generically chaotic. We use Laskar's frequency mapping technique to calculate the timescales for chaotic mixing in triaxial potentials with a range of cusp slopes and black hole masses. Preliminary results suggest that cusps steeper than \gamma\approx 1 lead to chaotic mixing timescales that are comparable to or less than galaxy lifetimes for the majority of boxlike orbits within the half-mass radius. Galaxies with steep cusps should therefore avoid triaxial shapes, since the parts of phase space associated with boxlike orbits would be populated nearly uniformly in such galaxies. This result is consistent with the observed lack of significant triaxiality in low-luminosity ellipticals, which always have steep cusps. We also show how to use the additional information on the structure of the phase space obtained from the frequency mapping technique to build self-consistent models of elliptical galaxies.
