PROFESSOR S. SRIDHAR

Planets orbiting a star, and many stars orbiting a massive black hole, are examples of Few-body (N < ten) and Many-body (N > million) self-gravitating systems. In both systems the Newtonian gravity of a central mass is the dominant force. The weaker mutual gravitational interactions between the other bodies drives the long-term (or secular) evolution of the system. Two problems of interest are: 1. Many planetary systems in binary stars have planets orbiting one star, with the companion star on a distant orbit. It is observed that the number of single-planet systems is much larger than the number of systems with multiple planets. A physical mechanism that can explain this fact will be discussed: gravitational forcing by the binary companion star on a distant orbit can resonate with secular planetary modes. This can have dramatic results ranging from the excitation of large planetary eccentricities and mutual inclinations, to disruption until just one planet is left. 2. The Andromeda galaxy has an eccentric and lopsided disc of stars orbiting a massive black hole; our Galactic Centre may have inclined and warped stellar components orbiting a massive black hole. These asymmetric structures could arise from broken symmetry states of a many- body system with long-range interactions and a compact phase space. A theoretical framework for the secular dynamics and statistical mechanics of stellar systems in galactic nuclei will be presented.