The role of bulges in the motion of stars in disks

Abstract

Using a modern galactic model that takes into account a dark matter halo, a spherical bulge and a disk, we study the nature of the orbit for star in the galaxy disk. Essentially, we study if the orbits of stars are stable or chaotic depending on the shape of the galaxy, specifically the ratio of the masses between the bulge and the disk of the galaxy. We also study the role of the star specific energy in the nature of the orbits. To analyse the trajectories of the stars we use Poincaré sections, a classical method that takes a qualitative approach to determine if the orbits calculated are regular or chaotic. We also take a more quantitative approach calculating the fraction of the area filled with regular orbits. Our results indicate that the stability of the orbits are highly dependent on the relation of masses between the bulge and the disk and the speci c energy of the star.