The dearth of nuclear star clusters in bright galaxies

TL;DR

This study uses N-body simulations to show that massive globular clusters are often destroyed before reaching galaxy centers with supermassive black holes over 10^8 solar masses, hindering nuclear star cluster formation.

Contribution

It demonstrates that SMBHs above 10^8 solar masses prevent globular clusters from reaching the galactic center, explaining the scarcity of nuclear star clusters in bright galaxies.

Findings

Massive GCs are dissolved before reaching inner galaxy regions when SMBH > 10^8 M_sun.

Destructive tidal interactions hinder nuclear star cluster formation in bright galaxies.

Close SMBH-GC interactions can produce stellar waves escaping the galaxy.

Abstract

We investigate the interaction of a massive globular cluster (GC) with a super massive black hole (SMBH), located at the centre of its host galaxy, by means of direct N-body simulations. The results show that tidal distortions induced by the stellar background and the SMBH act on a time shorter than that of dynamical friction decay for a $10^6$ M$_\odot$ GC whenever the SMBH mass exceeds $\sim 10^8$ M$_\odot$ . This implies an almost complete dissolution of the infalling GC before it reaches the inner region ($\lesssim 5$ pc) of the parent galaxy. The generalization of this result to a larger sample of infalling GCs shows that such destructive process may prevent the formation and growth of a bright galactic nucleus. Another interesting, serendipitous, result we obtained is that the close interaction between the SMBH and the GC produces a "wave" of stars that escape from the cluster and, in a fraction, even from the whole galaxy.