Aschenbach effect for spinning particles in Kerr-(A)dS spacetime

TL;DR

This study explores how spinning particles behave around rotating black holes with a cosmological constant, revealing that both particle spin and cosmological constant influence the Aschenbach effect, which can impact black hole spin measurements.

Contribution

It generalizes previous work by including the effects of particle spin and cosmological constant on the Aschenbach effect in Kerr-(A)dS spacetime.

Findings

Particle spin and cosmological constant modify the critical black hole spin for the Aschenbach effect.

Particle spin can mimic the effects of the cosmological constant, affecting measurements.

The critical spin value $a_c$ can increase or decrease depending on the signs of $s$ and $b3;.

Abstract

A non-monotonic behavior of the velocity gradient of a test particle revolving around a rapidly rotating black hole in the locally non-rotating frame of reference is known as the Aschenbach effect. This effect can serve as a distinguishing signature of rapidly rotating black holes, being potentially useful for the measurements of the astrophysical black hole spins. This paper is the generalization of our previous research to the motion of spinning particles around a rotating black hole with non-zero cosmological constant. We show that both the particle's spin $s$ and the cosmological constant $\Lambda$ modify the critical value of the black hole spin $a_c$, for which the Aschenbach effect can be observed; $a_c$ can increase or decrease depending on the signs of $s$ and $\Lambda$. We also found that the particle's spin $s$ can mimic the effect of the cosmological constant $\Lambda$ for a given $a_c$, causing thus a discrepancy in the measurements of $s$, $\Lambda$ and $a_c$ in the Aschenbach effect.