טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAharon Danor
SubjectStellar Dynamics near Massive Black Holes
in Nuclear Star Clusters
DepartmentDepartment of Physics
Supervisor Professor Hagai Perets
Full Thesis textFull thesis text - English Version


Abstract

My Ph.D. study aims at a detailed study of the stellar dynamics and properties of nuclear stellar clusters (NSC) in galactic nuclei and their implications for transient events such as tidal disruption events by massive black holes (MBHs) and extreme-mass ratio gravitational wave sources. The formation and evolution of NSCs and their structures depend on a wide variety of physical processes and the inter-relations between a variety of stellar populations and stellar systems, including stars, compact objects, and massive black holes. Relevant processes include dynamical processes, such as two-body relaxation processes and mass segregation, star formation processes and strong interactions of stars with the MBH though tidal disruptions of stars by the MBH and gravitational wave inspirals of compact objects. A wide range of tools and methods have been used to model the dynamics of NSCs, with most of the models focusing on a very limited number of processes while neglecting others. In this thesis I explore more realistic models for the evolution of NSCs, by combining several different physical processes and their mutual interactions, through the use of Fokker-Planck (FP) statistical physics methods and the effective introduction of the above mentioned processes and their coupling using the FP approach, thus allowing for the study of the long-term evolution of NSCs, which is otherwise too computationally prohibitive to explore through other methods. In particular, it provides for the first time the study of several elements including (1) the role of star formation in the dynamics of galactic nuclei, (2) the long-term evolution and history of of tidal disruption of stars by MBHs, (3) the role of age and mass segregation, (4) the dynamics of compact objects and non-trivial mass functions. These aspects, and in particular their combination have been little explored before, and my study provides a more coherent and realistic picture of the evolution of NSCs . Moreover, this study provides detailed predictions regarding (1) the rates and history of tidal disruption events, (2) the mass function of extreme-mass ratio gravitational wave sources, (3) the age-segregated structure of NSCs and the possible explanation for the origin of the core-like structure observed in the NSC of our own Milky-Way galaxy. The main results of this thesis have been published in three refereed papers. The submitted and published papers presented below are preceded by an introductory section and concluded by a summary section. The introduction presents the basic concepts and processes that are relevant for understanding the main concepts presented in this thesis. These include a description of various few-body interactions of stars with an MBH, and the interactions of stars and massive objects near MBHs. The latter interactions are presented in the context of relaxation processes, which govern the dynamics of stars near MBHs, and lead to scattering of stars into

Them.