by
Panos Patsis(Research Center for Astronomy, Academy of Athens)
→
Europe/Stockholm
FA32
FA32
Description
Structure observed in nature is usually associated with Order. In the
case of the galaxies with spiral arms the stars are supposed to follow
ordered, "regular", orbits. Ordered flows are typically described by
precessing ellipses corresponding to stable periodic orbits at
successive energies (Jacobi constants) in agreement with a density
wave scenario. This property is linked to the strength of the spirals
and their pattern speed. In the case of barred-spiral galaxies
however, the spirals extend beyond the end of the bars, located in
most cases close to the corotation of the system. In the corotation
region Chaos dominates and observed structures have to survive in this
dynamical environment. We will show how spiral arms in barred-spiral
systems can be supported by stars in chaotic motion "along" the
arms. The trajectories of these stars are associated with the
invariant manifolds of unstable periodic orbits at the corotation
region. There are even cases where chaotic orbits build also bars with
morphological properties similar to those of barred-spiral galaxies in
the local universe. Thus, Chaos is able to build structures in galaxies.
