Kiselev metric in the static and rotating form is widely used to test different aspects of the dark energy (
DE
) effects. We consider a
DE
Kiselev spacetime, predicting the reduction to the Kerr ...black hole (
BH
) solution under suitable conditions on the
DE
parameters and in this frame we study the effects of the dark energy on
BHs
and disks accretion. Elaborating a close comparison with the limiting vacuum Kerr spacetime, we focus on thick accretion disks around the central
BH
in the Kiselev solution, both co-rotating and counter-rotating with respect the central
BH
. We examine different aspects of
BH
accretion energetics by focusing on quantities related to the accretion rates and cusp luminosity, when considered the
DE
presence, related to the pure Kerr central
BH
. Our findings show that in these conditions heavy divergences with respect to the vacuum case are expected for the
DE
metrics. A known effect of the Kiselev metric is to lead to a false estimation the
BH
spin, we confirm this characteristic from the fluids dynamics analysis. Remarkably our results show that
DE
is affecting differently the accretion physics, and particularly the accretion rate, according to the fluid rotation orientation with respect to the central spinning attractor, leading in some cases to an under-estimation of the
BH
spin mass ratio. These contrasting aspects emerging in dependence on the fluids rotational orientation can be a distinguishing general
DE
feature which could lead to a revised observational paradigm where
DE
existence is considered.
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We study the accretion flows towards a central Kerr super-spinning attractor, discussing the formation of the flow inversion points, defined by condition
u
ϕ
=
0
on the particles flow axial velocity. ...We locate two closed surfaces, defining
inversion coronas
(spherical shells), surrounding the central attractor. The coronas analysis highlights observational aspects distinguishing the central attractors and providing indications on their spin and the orbiting fluids. The inversion corona is a closed region, generally of small extension and thickness, which is for the counter-rotating flows of the order of
≲
1.4
M
(central attractor mass) on the vertical rotational axis. There are no co-rotating inversion points (from co-rotating flows). The results point to strong signatures of the Kerr super-spinars, provided in both accretion and jet flows. With very narrow thickness, and varying little with the fluid initial conditions and the emission process details, inversion coronas can have remarkable observational significance for primordial Kerr super-spinars predicted by string theory. The corona region closest to the central attractor is the most observably recognizable and active part, distinguishing black holes solutions from super-spinars. Our analysis expounds the Lense–Thirring effects and repulsive gravity effects in the super-spinning ergoregions.
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We investigate ringed accretion disks composed of two tori (rings) orbiting on the equatorial plane of a central supermassive Kerr black hole. We discuss the emergence of the instability phases of ...each ring of the macro-configuration (ringed disk) according to the Paczynski violation of mechanical equilibrium. In the full general relativistic treatment, we consider the effects of the geometry of the Kerr spacetimes relevant to the characterization of the evolution of these configurations. The discussion of ring stability in different spacetimes enables us to identify particular classes of central Kerr attractors depending on their dimensionless spin. As a result of this analysis, we set constraints on the evolutionary schemes of the ringed disks relative to the torus morphology and on their rotation relative to the central black hole and to each other. The dynamics of the unstable phases of this system is significant for the high-energy phenomena related to accretion onto supermassive black holes in active galactic nuclei and the extremely energetic phenomena in quasars, which could be observed in their X-ray emission.
Our analysis focus on the dragging effects on the accretion flows and jet emission in Kerr super-spinars. These attractors are characterized by peculiar accretion structures as double tori, or ...special dragged tori in the ergoregion, produced by the balance of the hydrodynamic and centrifugal forces and also effects of super-spinars repulsive gravity. We investigate the accretion flows, constituted by particles and photons, from toroids orbiting a central Kerr super-spinar. As results of our analysis, in both accretion and jet flows, properties characterizing these geometries, that constitute possible strong observational signatures or these attractors, are highlighted. We found that the flow is characterized by closed surfaces, defining inversion coronas (spherical shell), with null the particles flow toroidal velocity (
u
ϕ
=
0
) embedding the central singularity. We proved that this region distinguishes proto-jets and accretion driven flows, co-rotating and counter-rotating flows. Therefore in both cases the flow carries information about the accretion structures around the central attractor, demonstrating that inversion points can constitute an observational aspect capable of distinguishing the super-spinars.
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5.
RINGED ACCRETION DISKS: INSTABILITIES Pugliese, D.; Stuchlík, Z.
The Astrophysical journal. Supplement series,
04/2016, Volume:
223, Issue:
2
Journal Article
Peer reviewed
Open access
ABSTRACT We analyze the possibility that several instability points may be formed, due to the Paczy ski mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive ...Kerr black hole. We consider a recently proposed model of a ringed accretion disk, made up by several tori (rings) that can be corotating or counter-rotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.
We study accretion tori and proto-jets in the field of central Kerr super-spinning attractors, exposing distinctions between Kerr naked singularities (NSs) and black holes (BHs). We focus on the ...spacetime regions very close to the central singularity, interior of the ergoregion, especially for slowly spinning NSs, where repulsive gravity effects emerge, discussing the causal structure in relation to tori contained, partially contained and confined in the ergoregion. We explore particularly regions close to the attractor rotational axis and the poles, where very slowly spinning tori, with momenta ℓ≈0, and axial cusp, constrained by the light surfaces, are relevant. Proto-jets (constraining jet emission) proved to be a signature in comparison with BH case, pointing out the emergence of very fast spinning tori in the ergoregion, very slow tori, double tori with internal cusp, and the presence of an axial cusp. The accretion disks properties point out very faster spinning attractors (extremely super spinning NSs). Providing distinguishable physical characteristics of jets and accretion tori, the differences between the BH and NS accretion scenarios, emerging from this analysis, constitute astrophysical tracers distinguishing NSs from BHs, and possible strong NSs observational signature of the primordial Kerr superspinars predicted by string theory.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We study several classes of exterior and interior axially symmetric spacetimes, such as wormholes, accelerating black holes, and binary black hole systems, from the point of view of light surfaces ...related to the generators of Killing horizons. We show that light surfaces constitute a useful framework for the study of the more diverse axially symmetric geometries. In particular, we point out the existence of common properties of the light surfaces in different spacetimes. We introduce a deformation of the Kerr–Newman metric and apply the light surfaces framework to analyze several generalizations in a compact form. As particular examples, we analyze static and spinning wormhole solutions, black holes immersed in external (perfect fluid) dark matter, spacetimes with (Taub) NUT charge, acceleration, magnetic charge, and cosmological constant, binary Reissner–Nordström black holes, a solution of a (low-energy effective) heterotic string theory, and the
(
1
+
2
)
dimensional BTZ geometry.
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We discuss the fundamentals of classical black hole (
BH
) thermodynamics in a new framework determined by light surfaces and their frequencies. This new approach allows us to study
BH
transitions ...inside the Kerr geometry. In the case of
BH
s, we introduce a new parametrization of the metric in terms of the maximum extractable rotational energy or, correspondingly, the irreducible mass, which is an alternative to the spin parametrization. It turns out that
BH
spacetimes with spins
a
/
M
=
8
/
9
and
a
/
M
=
1
/
2
show anomalies in the rotational energy extraction and surface gravity whereas the case
a
/
M
=
3
/
2
is of particular relevance to study the variations of the horizon area. We find the general conditions under which
BH
transitions can occur and express them in terms of the masses of the initial and final states. This shows that
BH
transitions in the Kerr geometry are not arbitrary but depend on the relationship between the mass and spin of the initial and final states. From an observational point of view, we argue that near the
BH
poles it is possible to detect photon orbits with frequencies that characterize the light surfaces analyzed in this work.
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