טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMikhaloff Diego Nathan
SubjectEvolution and Dynamics of Stellar Disks Around Massive
Black Holes
DepartmentDepartment of Physics
Supervisor Professor Hagai Perets
Full Thesis textFull thesis text - English Version


Abstract


We study the dynamical evolution of a stellar disk orbiting a massive black hole. We explore the role of two-body relaxation, mass segregation, stellar evolution and binary heating in affecting the disk evolution, and consider the impact of the nuclear cluster density and the stellar-disk mass-function. We use analytic arguments and apply them to study the evolution of the velocity dispersion of stars in a stellar disk (similar to that observed in the Galactic center; GC), both on the short (few Myr) and longer (100 Myr) evolutionary timescales. We find the dominant processes affecting the disk evolution are two-body relaxation and mass stratification, whereas binary heating have only a little contribution. Massive stars play a dominant role in kinematically heating low mass stars, and driving them to high eccentricities/inclinations. Multi-mass models with realistic mass-functions for the disk stars show that the disk structure to be mass stratified, with the most massive stars residing in thinner structures. Stellar evolution plays an important role in decreasing the number of massive stars with time, thereby leading to slower relaxation, where the remnant compact objects of these stars are excited to higher eccentricities/inclinations. At these later evolutionary stages dynamical heating by the nuclear cluster plays a progressively more important role. We conclude that the high eccentricities and high inclination observed for the majority on the young O-stars in the Galactic Center suggest that the disk stars had been formed with initially high eccentricities, or that collective or secular processes (not explored here) dominate the disk evolution. The latter processes are less likely to produce mass stratification in the disk; detailed study of the mass-dependent kinematic properties of the disk stars could therefore provide a handle on the processes that dominate its evolution. Finally, we find that the disk structure is expected to keep its coherency, and be observed as a relatively thin disk even after 100 Myr; two-body relaxation is too inefficient for the disk to assimilate into the nuclear cluster on such timescales. It therefore suggests earlier disks, now containing only older, lower mass stars, might still be observed in the Galactic center, unless destroyed/smeared by other non-two-body relaxation processes