Our aim is deepening the knowledge of the physics of the inner few parsecs of our Galaxy and of other galaxies.
The central regions of galaxies are very peculiar places, because they are sites of exotic objects like super massive black holes (SMBHs) and very massive and dense stellar clusters (Nuclear Star Clusters, NSCs). Moreover, the physical conditions are extreme, so to make them exceptional natural laboratories to test physical theories.
With this project, we intend to study better the inter-relation between the central local, small, space-time scales and those , much larger, of the overall galactic environment. Actually, galactic nuclei have sizes of ~ 10 pc and crossing times of few Myrs while galaxies extend to tens of kpc and orbital periods are Gyr long.
The existence of correlations between the inner part of a galaxy and the overall distribution is indirectly proven by the evidence of tight relations between the masses of SMBHs and the mass of the parent galaxy, as well by the evidence of a similar (although with different slope) correlation for the NSC mass and its host galaxy mass.
Moreover, observations of the so called "hyper velocity stars" (HVSs) in the Galactic halo seem to find an explanation only by mean of an acceleration mechanism caused by a central SMBH.
Our research will aim to interpretation of
i) the formation and evolution of galactic nuclei and their stellar and black hole content, ii) the possibility of formation and growth of a local SMBH by instability of a dense cluster of black holes; iii) the origin of HVSs and of the S-stars (the ones which orbit fast around the Galactic geometric center), as well as iv) check the possibility that either HVSs keep bound around them some revolving planets or they release them to the background as hypervelocity planets (HVPs).
This project is a continuation of a research driven by the applicant that in the past has produced relevant results and numerous publications at international level.
This project has specific innovative points, on the sides of the topics, aims (Physics and Astrophysics) and methods (algorithms and numerical methods) used.
Let us sketch some of these.
Topics: the study of inner galactic regions around massive and supermassive black holes is a highly debated topic in modern Astrophysics, especially after the recent discovery, by the Event Horizon telescope collaboration, of the evidence of an event horizon around the supermassive black hole in the giant elliptical galaxy M 87.
We have been working on the physics of the very dense environment around for many years. Our topics embrace the formation and evolution of CMOs as well as the topic of high- and hyper-velocity stars and planets in our Milky Way and other galaxies, which are fields still not completely covered by previous researches. Among the topics we are interested in, we cite that of the possible survival of planetary systems around the so called S-stars, which are the ones revolving closely to the CMO of our Galaxy (Sgr A*). At this regard, we are investigating on the possibility of picking via observations of stars approaching very closely the Sgr A* object the expected general relativistic effects of precession.
The interpretation, also, of the numerous data concerning the distribution of different types of stars (including RR Lyrae pulsators) in the galactic bulge is a modern topic which we attack in this project and of which we have already preliminary results.
Aims: the understanding of formation of NSCs and SMBHs, in the frame of violent dynamics in the inner galactic regions is an open question. In particular, one unsolved puzzle is that of the stability of the observed NSCs in galaxies.
Most of the galaxies borrow CMOs at their center, but there is a difference between very dense nuclear clusters and super massive black holes. It remains to understand if the missing evidence of NSCs in bright galactic hosts may be related to their collapse due to insufficient kinetic energy source to support the "heavy" gravitational structure.
Also the topic of generation of HVS with their planetary systems is new, as well as that of understanding the dynamical behavior of the "zoo" of compact objects strongly interacting in dense stellar environments.
A novel topic is that of the possible subsequent merging events of lighter black holes, to build up an eventual super massive black hole. This phenomenon would constitute a very important source of gravitational wave emission, never studied before.
Methods: we use state of the art dynamical simulations by means of direct summation, high precision codes developed in our group (HiGPUs, NBSymple, ARchain) or upon this specific collaboration (NBODY6++, phiGPU) or freely available. We will make use of both local (owned by the ASTRO group, lead by the project PI) computing platforms (CPU+GPUs hybrid systems) and huge parallel main frames via computing grants (supercomputer JJUWELS at the Gauss Centre for supercomputing, Julich, Germany).
A link to the expertise and activity of the ASTRO scientific group lead by R. Capuzzo Dolcetta is
https://sites.google.com/uniroma1.it/astrogroup/home