Non-monotonic Keplerian velocity profiles around near-extreme braneworld Kerr black holes

TL;DR

This paper investigates how non-monotonic Keplerian velocity profiles occur around near-extreme braneworld Kerr black holes and naked singularities, influenced by the tidal charge parameter, with implications for astrophysical observations.

Contribution

It demonstrates the conditions under which non-monotonic velocity profiles appear in braneworld Kerr spacetimes, highlighting the role of tidal charge and spin parameters.

Findings

Non-monotonic profiles exist for tidal charge less than 0.41005.

Higher spin values favor non-monotonic velocity profiles.

Decreasing tidal charge increases the velocity difference in the profiles.

Abstract

We study the non-monotonic Keplerian velocity profiles related to locally non-rotating frames (LNRF) in the field of near-extreme braneworld Kerr black holes and naked singularities in which the non-local gravitational effects of the bulk are represented by a braneworld tidal charge $b$ and the 4D geometry of the spacetime structure is governed by the Kerr-Newman geometry. We show that positive tidal charge has a tendency to restrict the values of the black hole dimensionless spin $a$ admitting existence of the non-monotonic Keplerian LNRF-velocity profiles; the non-monotonic profiles exist in the black hole spacetimes with tidal charge smaller than $b=0.41005$ (and spin larger than $a=0.76808$). With decreasing value of the tidal charge (which need not be only positive), both the region of spin allowing the non-monotonicity in the LNRF-velocity profile around braneworld Kerr black hole and the velocity difference in the minimum-maximum parts of the velocity profile increase implying growing astrophysical relevance of this phenomenon.