Perfect fluid tori orbiting Kehagias–Sfetsos naked singularities

Abstract

We construct perfect fluid tori in the field of the Kehagias-Sfetsos (K-S) naked singularities. These are spherically symmetric vacuum solutions of the modified Hořava quantum gravity, characterized by a dimensionless parameter ωM 2 , combining the gravitational mass parameter M of the spacetime with the Hořava parameter ω, reflecting the role of the quantum corrections. In dependence on the value of ωM 2 , the K-S naked singularities demonstrate a variety of qualitatively different behavior of their circular geodesics that is fully reflected in the properties of the toroidal structures, demonstrating clear distinction to the properties of the torii in the Schwarzschild spacetimes. In all of the K-S naked singularity spacetimes the tori are located above an "antigravity" sphere where matter can stay in a stable equilibrium position, which is relevant for the stability of the orbiting fluid toroidal accretion structures. The signature of the K-S naked singularity is given by the properties of marginally stable tori orbiting with the uniform distribution of the specific angular momentum of the fluid, l = const. In the K-S naked singularity spacetimes with ωM 2 > 0.2811, doubled tori with the same l = const can exist; mass transfer between the outer torus and the inner one is possible under appropriate conditions, while only outflow to the outer space is allowed in complementary conditions. In the K-S spacetimes with ωM 2 < 0.2811, accretion from cusped perfect fluid tori is not possible due to the non-existence of unstable circular geodesics.

Iron Kα line of boson stars

“…In the Kerr spacetime and in many other spacetimes, dΩ K /dr < 0, and the magneto-rotational instability (MRI), which is the standard mechanism to drive the accretion process in Keplerian disks, can work. However, there are examples of non-Kerr spacetimes where there are at least regions with stable equatorial circular orbits where dΩ K /dr < 0 does not hold [87][88][89]. In such a case, the presence of a Keplerian disk at those radii would only be possible in the presence of an alternative mechanism to generate the necessary viscosity effects to enable the accretion of matter.…”

Gravitational lensing around Kehagias–Sfetsos compact objects surrounded by plasma

“…Hořava gravity touches the realm of the quantum gravity and strong lensing analysis in the vicinity of KS can give constraints of parameters defining black hole spacetime and corresponding link between GR and quantum gravity. In fact, there is a series of works treating the astrophysical phenomena in the vicinity of KS black hole [17] and works related to KS naked singularities [18,19,20,21].…”

Polish Doughnuts around Scalarized Kerr Black Holes

“…GRMHD simulations with a similar setup are also used to address advection-dominated flows, the evolution of weakly magnetized disks, jet formation and the differences between possible images of black holes and boson stars (BS) [7,8,9,10,11,12]. Outside the context of GRMHD simulations, Polish doughnuts are also used to address possible tori geometries around exotic spacetimes such as Kerrde Sitter backgrounds, distorted static BHs, deformed compact objects, Kehagias-Sfetsos naked singularities and BSs [13,14,15,16,17,18,19]. Although some models of doughnuts may include magnetic fields and non-constant specific angular momentum distribution, the constant specific angular momentum case remains being an important first step in this field of research, since in this case the torus solutions are marginally stable for Kerr BHs and hold similar topologies as the ones found for different specific angular momentum distributions [20,21].…”