The secular evolution of a uniform density star cluster immersed in a compressible galactic tidal field

TL;DR

This paper analytically investigates how uniform density star clusters can survive in galactic centers' tidal fields, suggesting they may migrate inward without disruption and contribute to nuclear cluster formation.

Contribution

It provides an analytical model for the secular evolution of uniform density star clusters in galactic tidal fields, highlighting conditions for their survival and inward migration.

Findings

Clusters can survive closer to galactic centers than traditional tidal disruption radius.

Shallow galactic potential allows tidal compression rather than disruption.

Analytical results suggest possible inward migration of clusters without destruction.

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.