### Complex dynamics of fast spinning neutron stars around a massive black hole

Prof. Kinwah Wu

Strongly bound gravitational systems often show interesting dynamical phenomena. Spinning finite-size objects in gravity would not follow geodesics in the space-time manifold. A fast spinning neutron stars or a neutron-star system orbiting around a black hole would exhibit complex spin and orbital behaviours due to various relativistic coupling. This project investigates two special classes of black hole - neutron star systems:

(1) a fast spinning NS orbiting around a BH, and

(2) a double neutron-star system orbiting around a BH (which is a hierarchical 3-body system).

In (1) spin-curvature coupling leads to non-planar NS orbits, in addition to de-Sitter and Lense-Thirring precessions of the neutron star's spin. In (2) orbit-orbit coupling induces gravito-magnetism, which manifests in the complex orbital and spin motion of the double neutron-star system. Radio pulsar timing and gravitational wave observations will be able to study the dynamical properties of these systems. Black hole - neutron star systems are useful in the study of fundamental physics and in astrophysics. They can be used to map the space-time structure around black holes and to determine the masses and spins of the massive nuclear black holes in galaxies. This is a theoretical project. It involves phenomenological modelling, algebraic computation and numerical calculations.