**Publication date:** Aug 2023

**Abstract:**

A way to test electromagnetic field and spacetime properties around black holes is by considering the dynamics of test particles. In fact, in real astrophysical scenarios, it is hard to determine spacetime geometry which is dominating due to degeneracy gravitational effects in parameters of gravity theories. In this work, we study for the first time the dynamics of spinning particles that have magnetic dipole moments around Schwarzschild black holes immersed in an external asymptotically uniform magnetic field using the Mathisson-Papapetrou-Dixon (MPD) equation. There are two combined interactions: gravitational interaction between the spin of the particle and (electro)magnetic interaction between the external magnetic field and the magnetic dipole moment of the particle to be taken into account. First, we derive the effective potential of the test spinning magnetized particles in motion around the black hole. We also study the combined effects of spin and magnetic interactions on innermost stable circular orbits (ISCOs), the energy, and angular momentum of the particles at ISCO together with superluminal bounds. We investigated the collision of the particles and evaluated the center-of-mass energy in the collisions. Finally, we consider various cases in which neutron stars and rotating stellar mass black holes can be treated as spinning magnetized particles, evaluating the effects of the spin and magnetic moment of objects around supermassive and intermediate-mass black holes. It is also found that magnetic interaction effects are much larger than spin ones in the case of a neutron star orbiting a supermassive mass black hole, while for the case of a neutron star and intermediate-mass black hole system, the effects are comparable where the magnetic field value is larger than 20 G for typical neutron stars and this value for the system with rotating stellar mass black holes is about 280 G.

**Authors:**

Abdulxamidov, Farrux; Rayimbaev, Javlon; Abdujabbarov, Ahmadjon; Stuchlík, Zdeněk;