Rotating dirty black hole and its shadow

Physics of the Dark Universe

We consider Kerr black holes (BHs) surrounded by perfect dark fluid matter (PFDM), with an additional parameter (k) because of PFDM, apart from mass (M) and rotation parameter (a)the rotating PFDM BHs. We analyse the photon orbits around PFDM BHs and naked singularities (NSs) and emphasize the effect of PFDM on photon boomerangs. Interestingly, the azimuthal oscillations first increase and then decrease for retrograde orbits, whereas they first decrease and then increase for prograde orbits, with increasing k. Unlike in the Kerr NSs, photon boomerangs can form around rotating PFDM NSs. We use the Event Horizon Telescope (EHT) observational results for Schwarzschild shadow deviations of M87* and Sgr A*, δM87 * = −0.01 ± 0.17 and δSgrA * = −0.08 +0.09 −0.09 (VLTI), −0.04 +0.09 −0.10 (Keck), to report the upper bounds on the PFDM parameter: 0 ≤ k ≤ 0.0792M and k max ∈ [0.0507M, 0.0611M ] respectively. Together with the EHT bounds on the shadows of Sgr A * and M87 * , our analysis concludes that a substantial part of the rotating PFDM BH parameter space agrees with the EHT observations. Thus, one must consider the possibility of the rotating PFDM BHs being strong candidates for the astrophysical BHs.

The European Physical Journal C

This paper investigates the circular motion of neutral test particles orbiting near Kerr-Newman black hole in the presence of quintessential dark energy and cosmological constant. We limit our analysis to the equatorial plane and explore the properties of both time-like and null geodesics. The behavior of the specific energy and the angular momentum of the co-rotating as well as the counter rotating particles is analyzed. We also discuss the stable regions with respect to the horizons, radius of photon sphere and the so called static radius. We have shown that the stable points are always less than the static radius while they exceed the radius of photon orbit. The energy extraction, negative energy state and energy gain during the Penrose process is also discussed. It is found that more energy can be gained during the Penrose process in the presence of dark energy as compared to the charge and spin of the said black hole.

2021

In this paper, we discussed the possible effects of dark matter on a Schwarzschild black hole with extended uncertainty principle (EUP) correction such as the parameter α and the large fundamental length scale L∗. In particular, we surrounded the EUP black hole of mass m with a static spherical shell of dark matter described by the parameters mass M , inner radius rs, and thickness ∆rs. Considering only the case where the EUP event horizon coincides rs, the study finds that there is no deviation in the event horizon, which readily implies that the black hole temperature due to the Hawking radiation is independent of any dark matter concentration. In addition, we explored the deviations in the innermost stable circular orbit (ISCO) radius of time-like particles, photonsphere, shadow radius, and weak deflection angle. It is found that time-like orbits are sensitive to deviation even for low values of mass M. A greater dark matter density is needed to have considerable deviations to nu...

Classical and Quantum Gravity, 2021

In this work we have obtained a charged black hole solution in the presence of perfect fluid dark matter (PFDM) and discuss its energy conditions. The metric corresponding to the rotating avatar of this black hole solution is obtained by incorporating the Newman–Janis algorithm. We then compute two types of circular geodesics, namely, the null geodesics and time-like geodesics for this rotating spacetime geometry. For the case of time-like geodesics, we consider both neutral as well as charged massive particles. The effective potentials of the corresponding circular geodesics has also been studied. We then present our results by graphically representing the collective effects of the black hole parameters, namely, the charge of the black hole (Q), spin parameter (a) and the PFDM parameter (α) on the energy (E), angular momentum (L) and effective potential (V eff) of the concerned particle. Finally, we discuss the Penrose process in order to study the negative energy particles having ...

2020

The existence of quintessential dark energy around a black hole has considerable consequences on its spacetime geometry. Hence, in this article, we explore its effect on horizons and the silhouette generated by a Kerr–Newman black hole in quintessential dark energy. Moreover, to analyse the deflection angle of light, we utilize the Gauss-Bonnet theorem. The obtained result demonstrates that, due to the dragging effect, the black hole spin elongates its shadow in the direction of the rotational axis, while increases the deflection angle. On the other hand, the black hole charge diminishing its shadow, as well as the angle of light’s deflection. Besides, both spin and charge significantly increase the distortion effect in the black hole’s shadow. The quintessence parameter γ, increases the shadow radius, while decreases the distortion effect at higher values of charge and spin parameters.

Physical Review D, 2019

Classical and Quantum Gravity

We analysed the shadow cast by charged rotating black hole (BH) in presence of perfect fluid dark matter (PFDM). We studied the null geodesic equations and obtained the shadow of the charged rotating BH to see the effects of PFDM parameter $\gamma$, charge $Q$ and rotation parameter $a$, and it is noticed that the size as well as the shape of BH shadow is affected due to PFDM parameter, charge and rotation parameter. Thus, it is seen that the presence of dark matter around a BH affects its spacetime. We also investigated the influence of all the parameters (PFDM parameter $\gamma$, BHs charge $Q$ and rotational parameter $a$) on effective potential, energy emission by graphical representation, and compare all the results with the non rotating case in usual general relativity. To this end, we have also explored the effect of PFDM on the deflection angle and the size of Einstein rings.

Classical and Quantum Gravity

In this work, we consider a rotating charged black hole surrounded by perfect fluid dark matter. We consider the system to be immersed in non-magnetised, pressureless plasma. First, we evaluate the null geodesics in order to study the co-rotating and counter rotating photon orbits. Further, we analyse the null geodesics to calculate the celestial coordinates (α, β). The celestial coordinates are used to determine the black hole shadow radius (R s). Thereafter, we observe and analyse the effects of black hole spacetime, perfect fluid dark matter and plasma parameters (a, Q, χ, k) on the black hole shadow in detail. Finally, we study the effect of plasma distribution on the effective potential (V eff) of the black hole spacetime as encountered by the photons. We also present bounds on the plasma parameter from the observational data from M87* central supermassive black hole.

Journal of Cosmology and Astroparticle Physics, 2019

We consider applications of the curvature radius of a Kerr black hole shadow and propose three new approaches to simultaneously determine the black hole spin and inclination angle of the observer. The first one uses only two symmetric characteristic points, i.e., the top and the bottom points of the shadow, and is the smallest amount of data employed to extract information about spin and inclination angle amongst all current treatments. The second approach shows that only measuring the curvature radius at the characteristic points can also yield the black hole spin and the inclination angle. The observables used in the third approach have large changes to the spin and the inclination angle, which may give us a more accurate way to determine these parameters. Moreover, by modeling the supermassive black hole M87* with a Kerr black hole, we calculate the angular size for these curvature radii of the shadow. Some novel properties are found and analyzed. The results may shine new light on the relationship between the curvature radius and the black hole shadow, and provide several different approaches to test the nature of the black hole through the shadow.

The European Physical Journal C

The detailed study of horizon structure and the shadow cast by a Kerr-like black hole (BH) is performed. The trajectory of light rays forming the shadow of BH is found using the solutions of geodesic equation for the motion and effective potential of a photon around Kerr-like BH for different values of deviation parameter l in Kerr-like spcetime metric. It is observed that with an increase in the parameter l the size of the shadow of the BH is decreased. Additional, we have consider effect of plasma on BH shadow and the plasma influence on the shadow of Kerr-like BH, the size of observable radius of BH shadow and oblateness are explored with more details.