Regular frames and particle's rotation near a black hole

TL;DR

This paper investigates the number of revolutions a particle makes around a rotating black hole using regular frames on the horizon, revealing differences between extremal and nonextremal black holes and comparing methods.

Contribution

It introduces a new approach using horizon-regular frames to analyze particle revolutions, avoiding subtraction procedures for nonextremal black holes.

Findings

Number of revolutions is finite for nonextremal black holes without subtraction.

For extremal black holes, results differ depending on the method used.

Regular frames provide a consistent framework near the horizon.

Abstract

We consider a particle moving towards a rotating black hole. We are interested in the number of its revolution $n$ around a black hole. In our previous work (Pavlov and Zaslavskii in Gen Relativ Gravit 50: 14, 2018. arXiv:1707.02860) we considered this issue in the Boyer-Lindquist type of coordinates with a subsequent procedure of subtraction. Now, we reconsider this issue using from the very beginning the frames regular on the horizon. For a nonextremal black hole, regularity of a coordinate frame leads to the finiteness of a number of revolutions around a black hole without a subtraction procedure. Meanwhile, for extremal black holes comparison of $n$ calculated in the regular frame with some subtraction procedures used by us earlier shows that the results can be different.