Globular cluster-massive black hole interactions in galactic centers

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.Comment: 4 pages, 1 fiugre. Presented at the MODEST 16/Cosmic Lab conference in Bologna, Italy, April 18-22 2016. To be pusblshed in Mem. S.A.It. Conference Serie

Evolution of the Globular Cluster System in a Triaxial Galaxy

Dynamical friction and tidal disruption are effective mechanisms of evolution of globular cluster systems, especially in non-axysimmetric galaxies with a central compact nucleus. With a semi-analytical approach based on the knowledge of the dependence of the dynamical friction and tidal disruption effects on the relevant parameters, we are able to follow the time evolution of the globular cluster system in a model of a triaxial galaxy and give its observable properties to compare with observational data. An important result is that the flatter distribution of the globular cluster system relatively to that of the stellar bulge, as observed in many galaxies, can be explained by the evolution of the globular cluster system, starting from the same density profile.Comment: 9 pages, including 7 eps figures; latex file using standard MNRAS style file. Paper submitted to MNRA

An efficient parallel tree-code for the simulation of self-gravitating systems

We describe a parallel version of our tree-code for the simulation of self-gravitating systems in Astrophysics. It is based on a dynamic and adaptive method for the domain decomposition, which exploits the hierarchical data arrangement used by the tree-code. It shows low computational costs for the parallelization overhead -- less than 4% of the total CPU-time in the tests done -- because the domain decomposition is performed 'on the fly' during the tree setting and the portion of the tree that is local to each processor 'enriches' itself of remote data only when they are actually needed. The performances of an implementation of the parallel code on a Cray T3E are presented and discussed. They exhibit a very good behaviour of the speedup (=15 with 16 processors and 10^5 particles) and a rather low load unbalancing (< 10% using up to 16 processors), achieving a high computation speed in the forces evaluation (>10^4 particles/sec with 8 processors).Comment: 10 pages, 8 figures, LaTeX2e, A&A class file needed (included), submitted to A&A; corrected abstract word wrappin

High velocity stars from close interaction of a globular cluster and a super massive black hole

Observations show the presence, in the halo of our Galaxy, of stars moving at velocities so high to require an acceleration mechanism involving the presence of a massive central black hole. Thus, in the frame of a galaxy hosting a supermassive black hole ($10^8$ $M_{\odot}$) we investigated a mechanism for the production of high velocity stars, which was suggested by the results of N-body simulations of the close interaction between a massive, orbitally decayed, globular cluster and the super massive black hole. The high velocity acquired by some stars of the cluster comes from the transfer of gravitational binding energy into kinetic energy of the escaping star originally orbiting around the cluster. After the close interaction with the massive black hole, stars could reach a velocity sufficient to travel in the halo and even overcome the galactic gravitational well, while some of them are just stripped from the globular cluster and start orbiting on precessing loops around the galactic centre.Comment: 15 pages, 9 figures, 2 Tables, accepted for publication in MNRA