Aschenbach effect for spinning particles in Kerr\u2013(A)dS spacetime

Ali Vahedi,Arman Tursunov,Jafar Khodagholizadeh

doi:10.1140/epjc/s10052-021-09081-0

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.

Highlights

The most fundamental among the parameters of a black hole is its mass, which in many cases is measured through the direct observations of nearby objects with relatively high accuracy
We found that the particle’s spin s can mimic the effect of the cosmological constant for a given ac, causing a discrepancy in the measurements of s, and ac in the Aschenbach effect
Among the promising avenues for the spin determination of astrophysical black hole is potential gravitational waves detections from extreme mass ratio inspirals (EMRI) by future space-based Laser Interferometer Space Antenna (LISA) [6]

Summary

Introduction

The most fundamental among the parameters of a black hole is its mass, which in many cases is measured through the direct observations of nearby objects with relatively high accuracy. If the spin of a supermassive black hole is near-extremal (with a > 0.9953), the Aschenbach effect can be observed for co-rotating matter through the corresponding change of the radiation flux at different radial positions of accretion disk or the flares. Another interesting possibility to observe the Aschenbach effect is through the detection of gravitational waves from EMRI by future LISA experiment [6]. In this paper we study the dynamics of a spinning particle in the vicinity of a rotating black hole with non-vanishing cosmological constant, focusing on (but not restricted to) the generalization of the Aschenbach effect in the Kerr–(A)dS metric spacetime.

Review on Mathisson–Papapetrou–Dixon equations

Aschenbach effect for non-spinning particle with non-zero

Aschenbach effect: general case

Conclusion