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Dissipative motion in galaxies with non-axisymmetric potentials
Due to the clumpy nature of the self gravitating gas composing the
interstellar medium, it is not clear whether galactic gas dynamics can be
discussed in terms of standard hydrodynamics. Nevertheless, it is clear that
certain generic properties related to orbital structure in a given potential
and the effect of dissipation can be used to qualitatively understand gas
motion in galaxies. The effect of dissipation is examined in triaxial galaxy
potentials with and without rotating time dependent components. In the former
case, dissipative trajectories settle around closed loop orbits when these
exist. When they do not, e.g., inside a constant density core, then the only
attractor is the centre and this leads to mass inflow. This provides a self
regulating mechanism for accession of material towards the centre --- since the
formation of a central masses destroys the central density core and eventually
stops the accession. In the case when a rotating bar is present, there are
usually several types of attractors, including those on which long lived
chaotic motion can occur (strange attractors). Motion on these is erratic with
large radial and vertical oscillations.Comment: Contibution to the conference on ``Astrophysical Fluids: From Atomic
Nuclei to Stars and Galaxies'' (in honour of Giora Shaviv's 60 th birthday).
To appear in Physics Report
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