Chaotic orbits in a galaxy model with a massive nucleus

The transition from regular to chaotic motion is studied in an axially symmetric galaxy model with a disk-halo and a spherical nucleus. This model has the characteristic that the mass of the nucleus increases exponentially, because mass is transported from the disk to the nucleus while the total mass of the galaxy remains constant. Stars with values of angular momentum L-z less or equal to a critical value L-zc, moving near the galactic plane, are scattered to the halo when approaching the nucleus. The corresponding orbits are chaotic. A linear relationship is found to exist between the critical angular momentum and the final mass of the nucleus M-nf. Our results suggest that the stars in the central regions of disk galaxies with massive nuclei must be in chaotic orbits. Comparison with previous work is also made.