The Secular Evolution of a Uniform Density Star Cluster Immersed in a Compressible Galactic Tidal Field

Abstract

Nuclear stellar clusters are common in the center of galaxies. We consider the possibility that their progenitors assumed to be globular clusters may have formed elsewhere, migrated to, and assembled near their present location. The main challenge for this scenario is whether globular clusters can withstand the tidal field of their host galaxies. Our analysis suggests that provided the mass-density distribution of background potential is relatively shallow, as in some galaxies with relatively flat surface brightness profiles, the tidal field near the center of galaxies may be shown to be able to compress rather than disrupt a globular cluster at a distance from the center much smaller than the conventionally defined “tidal disruption radius” r t . To do so, we adopt a previously constructed formalism and consider the secular evolution of star clusters with a homogeneous mass-density distribution. We analytically solve the secular equations in the limit that the mass density of stars in the galactic center approaches a uniform distribution. Our model indicates that a star cluster could travel to distances much smaller than r t without disruption, thus potentially contributing to the formation of the nuclear cluster. However, appropriate numerical N -body simulations are needed to confirm our analytic findings.