# Spin dynamics of moving bodies in rotating black hole spacetimes

## TL;DR

This paper investigates the complex spin dynamics of test bodies in various rotating black hole spacetimes, revealing effects like amplitude modulation, rapid spin variation near ergospheres, and differences across black hole types.

## Contribution

It provides a detailed numerical analysis of spin-curvature coupling effects on test bodies in Kerr, Bardeen-like, and Hayward-like black hole spacetimes, including regular black holes.

## Key findings

- Amplitude modulation in spin precession for high spins.
- Rapid spin variation near and inside ergospheres.
- Differential effects of spin-curvature coupling across black hole types.

## Abstract

The dynamics of spinning test bodies, moving in rotating black hole (Kerr, Bardeen-like and Hayward-like) spacetimes, are investigated. In Kerr spacetime, all the spherical, zoom-whirl and unbound orbits are considered numerically. Along spherical orbits and for high spin, an amplitude modulation is found in the harmonic evolution of the spin precessional angular velocity, caused by the spin-curvature coupling. Along the discussed zoom-whirl and unbound orbits, the test body approaches the center so much that it passes through the ergosphere. Near and inside the ergosphere, the variation of the spin direction can be very rapid. The effects of the spin-curvature coupling is also investigated. The initial values are chosen such a way, that the body and its spin move in the equatorial plane of the coordinate space and of the comoving frame, respectively. Hence, a clear effect of the spin-curvature coupling is observed as the orbit and the spin vector leave the equatorial plane. Additional effects in the spin precessional angular velocity and in the evolution of the Boyer-Lindquist coordinate components of the spin vector is also considered. Finally, in case of different regular black holes, the spin-curvature coupling influences differently the orbit and the spin evolutions.