In General Relativity, there are accelerating rotating black holes whose acceleration is not produced by a cosmic string, but by the interaction between the black hole spin and a rotating ("swirling") gravitational background. In this project, the student will test this interpretation with a simple model: a spinning test particle in the swirling universe. The goal is to compute the spin–curvature force along the symmetry axis, show that it produces a uniformly accelerated motion, and compare the result with the regularity condition of the exact solution.