The physics of the inner few parsecs of our Galaxy and of other galaxies is poorly known, because of its extreme conditions.
Actually, the central regions of galaxies are 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). This implies that physical conditions are extreme, to make them exceptional natural laboratories to test physical theories under conditions unreachable elsewhere.
This project aims to a deeper study of the inter-relation between the central local, small, space-time scales and those , much larger, of the overall galactic environment: 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. In spite of these huge differences, there is a clear observational evidence that the characteristics and properties of the inner, dense nuclear regions of galaxies are correlated to the much wider overall structure.
In particular, it has been shown that in bright galaxies a central SMBH is almost always present, while in fainter ones is usually present a dense central NSC.
In such frame, our project aims to pursue our investigation about:
i) the formation and evolution of galactic nuclei and their stellar and black hole content, ii) the formation and growth of a local SMBH by instability of a dense cluster of intermediate mass black holes; iii) the dynamics of S-stars (those passing by the Sgr A* Galactic black hole) is influenced by the local very strong field out of the Newtonian regime; iv) the origin of the hyper velocity stars as well as iv) the possibility that either HVSs keep bound around them some revolving planets or they release them to the background as hypervelocity planets.
This project is a continuation of a research driven by the applicant that in the past has produced relevant results and numerous publications at high international level.
This project presents numerous innovative points, on the sides of the topics, aims (Physics and Astrophysics) and methods (algorithms and numerical methods) used.
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. Even more relevant, the 2 Nobel prizes awarded to R. Genzel and A. Ghez for their detailed analysis of the motion of stars passing very close to the Galactic center, to determine the mass of the Sgr A* (possible) black hole.
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 modern 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. We would compare the observed apside line precessions with that we can compute under different hypothesis (fully General relativity in presence of a non-spinning or spinning blacvk hole; Poste Newtonian approximation of GR up to various orders, etc.).
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 intermediate mass 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, ARWV) or upon this specific collaboration (NBODY6++, phiGPU) or freely available. We will make use of both ocal (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