Exploring the origin, the nature and the dynamical behaviour of distant
  stars in galaxy models
  We explore the regular or chaotic nature of orbits moving in the meridional
plane of an axially symmetric galactic gravitational model with a disk, a dense
spherical nucleus and some additional perturbing terms corresponding to
influence from nearby galaxies. In order to obtain this we use the Smaller
ALingment Index (SALI) technique integrating extensive samples of orbits. Of
particular interest is the study of distant, remote stars moving in large
galactocentric orbits. Our extensive numerical experiments indicate that the
majority of the distant stars perform chaotic orbits. However, there are also
distant stars displaying regular motion as well. Most distant stars are ejected
into the galactic halo on approaching the dense and massive nucleus. We study
the influence of some important parameters of the dynamical system, such as the
mass of the nucleus and the angular momentum, by computing in each case the
percentage of regular and chaotic orbits. A second order polynomial
relationship connects the mass of the nucleus and the critical angular momentum
of the distant star. Some heuristic semi-theoretical arguments to explain and
justify the numerically derived outcomes are also given. Our numerical
calculations suggest that the majority of distant stars spend their orbital
time in the halo where it is easy to be observed. We present evidence that the
main cause for driving stars to distant orbits is the presence of the dense
nucleus combined with the perturbation caused by nearby galaxies. The origin of
young O and B stars observed in the halo is also discussed.
