Final Report Summary - FDP-MBH (Fundamental dynamical processes near massive black holes in galactic nuclei)
This project combined analytical studies and computer simulations to explore fundamental questions in the dynamics and statistical mechanics of stars near massive black holes (MBHs). These are directly linked to key astrophysical, cosmological and basic physics issues such as the growth and evolution of single and binary MBHs and the connections to the evolution of the host galaxy; the rate of supply of single and binary stars to the black hole and their tidal heating, destruction, scattering, capture or ejection; the rate and modes of gravitational wave emission from captured compact objects and from the mergers of binary MBHs; and the emergence of exotic stellar populations around MBHs.
Our most important achievements are:
1. The discovery that the slowest mode of randomization of such systems, by 2-body relaxation, is an anomalous diffusion process, where “unlikely” strong scattering events are in fact not so rare. We confirmed that the long-term effects of this process imply that passively evolving galactic nuclei with lower-mass black holes should be dynamically relaxed.
2. The discovery of a new mode of mass segregation (the tendency of the more massive stars to sink to the center), named “strong mass segregation”, where the massive stars tend to concentrate very sharply at the center, near the MBH. This increases the rates of strong interactions of stars with the MBH.
3. We demonstrated that an “exotic” fast form of relaxation of angular momentum, Resonant Relaxation, dominates almost all facets of evolution in the environment near MBHs in galactic nuclei. In particular, it strongly affects the dynamics of small compact objects that fall into MBHs and emit gravitational waves, through the newly found and still not fully understood phenomenon of the Schwarzschild Barrier. Resonant relaxation will also interfere with attempts to test basic predictions of General Relativity with the orbits of stars around the Galactic MBH, and affect the dynamics of the unusual population of young stars that are seen orbiting around it.
4. We discovered, and modelled for the first time, the strong effects of resonant stellar torques on accretion disks that feed MBHs. These can strongly influence the geometry, properties and variability of accretion disks, and thereby affect the cosmic evolution of both the mass and spin of MBHs.
Our most important achievements are:
1. The discovery that the slowest mode of randomization of such systems, by 2-body relaxation, is an anomalous diffusion process, where “unlikely” strong scattering events are in fact not so rare. We confirmed that the long-term effects of this process imply that passively evolving galactic nuclei with lower-mass black holes should be dynamically relaxed.
2. The discovery of a new mode of mass segregation (the tendency of the more massive stars to sink to the center), named “strong mass segregation”, where the massive stars tend to concentrate very sharply at the center, near the MBH. This increases the rates of strong interactions of stars with the MBH.
3. We demonstrated that an “exotic” fast form of relaxation of angular momentum, Resonant Relaxation, dominates almost all facets of evolution in the environment near MBHs in galactic nuclei. In particular, it strongly affects the dynamics of small compact objects that fall into MBHs and emit gravitational waves, through the newly found and still not fully understood phenomenon of the Schwarzschild Barrier. Resonant relaxation will also interfere with attempts to test basic predictions of General Relativity with the orbits of stars around the Galactic MBH, and affect the dynamics of the unusual population of young stars that are seen orbiting around it.
4. We discovered, and modelled for the first time, the strong effects of resonant stellar torques on accretion disks that feed MBHs. These can strongly influence the geometry, properties and variability of accretion disks, and thereby affect the cosmic evolution of both the mass and spin of MBHs.