  Many, if not all, galaxies host massive compact objects at their centers.
They are present as singularities (super massive black holes) or high density
star clusters (nuclear tar clusters). In some cases they coexist, and interact
more or less strongly. In this short paper I will talk of the 'merger' globular
cluster scenario, which has been shown in the past to be an explanation of the
substantial mass accumulation in galactic centers. In particular, I will
present the many astrophysical implications of such scenario pointing the
attention on the mutual feedback of orbitally decaying globular clusters with
massive and super massive black holes.
