Strong gravitational lensing around dilaton–axion black holes having special coupling with electromagnetic field

2021 ◽  
Author(s):  
Tanwi Ghosh ◽  
Amna Ali
Keyword(s):  
Black Holes ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Strong Field ◽  
Observational Evidence ◽  
The Other ◽  
Strong Gravitational Lensing ◽  
The Galaxy ◽  
The Deflection Angle ◽  
Lensing Effect

Recent observational evidence reveals the existence of black holes in the galaxy. Using strong field lensing effect, we find out the expressions of the radius of the photon sphere, the deflection angle, the separation between the first and the other images, the ratio between the flux of the first image as well as the flux coming from all the other images for dilaton–axion black holes and compare the results with Reissner–Nordstrom black holes. We also investigate the variations of primary and secondary image positions as well as their magnifications with respect to the source position for this kind of black holes.

scholarly journals Gravitational lensing by a black hole with torsion

2018 ◽  
Vol 27 (12) ◽  
pp. 1850110 ◽  
Author(s):  
Lu Zhang ◽  
Songbai Chen ◽  
Jiliang Jing
Keyword(s):  
Gravitational Lensing ◽  
Deflection Angle ◽  
Strong Field ◽  
Spherically Symmetric ◽  
Field Limit ◽  
Strong Gravitational Lensing ◽  
Spacetime Structure ◽  
Higher Order Terms ◽  
The Deflection Angle ◽  
Special Case

In this paper, we have investigated the gravitational lensing in a spherically symmetric spacetime with torsion in the generalized Einstein–Cartan–Kibble–Sciama (ECKS) theory of gravity by considering higher order terms. The torsion parameters change the spacetime structure, which affects the photon sphere, the deflection angle and the strong gravitational lensing. The condition of existence of horizons is not inconsistent with that of the photon sphere. Especially, there exists a novel case in which there is horizon but no photon sphere for the considered spacetime. In this special case, the deflection angle of the light ray near the event horizon also diverges logarithmically, but the coefficients in the strong-field limit are different from those in the cases with photon sphere. Moreover, in the far-field limit, we find that the deflection angle for certain torsion parameters approaches zero from the negative side, which is different from those in the usual spacetimes.

scholarly journals Gravitational lensing by charged black hole in regularized 4D Einstein–Gauss–Bonnet gravity

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Rahul Kumar ◽  
Shafqat Ul Islam ◽  
Sushant G. Ghosh
Keyword(s):  
Black Holes ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Strong Field ◽  
Angular Position ◽  
Angular Separation ◽  
Light Deflection ◽  
Charged Black Holes ◽  
The Deflection Angle ◽  
Sgr A

AbstractAmong the higher curvature gravities, the most extensively studied theory is the so-called Einstein–Gauss–Bonnet (EGB) gravity, whose Lagrangian contains Einstein term with the GB combination of quadratic curvature terms, and the GB term yields nontrivial gravitational dynamics in $$ D\ge 5$$ D ≥ 5 . Recently there has been a surge of interest in regularizing, a $$ D \rightarrow 4 $$ D → 4 limit of, the EGB gravity, and the resulting regularized 4D EGB gravity valid in 4D. We consider gravitational lensing by Charged black holes in the 4D EGB gravity theory to calculate the light deflection coefficients in strong-field limits $$\bar{a}$$ a ¯ and $$\bar{b}$$ b ¯ , while former increases with increasing GB parameter $$\alpha $$ α and charge q, later decrease. We also find a decrease in the deflection angle $$\alpha _D$$ α D , angular position $$\theta _{\infty }$$ θ ∞ decreases more slowly and impact parameter for photon orbits $$u_{m}$$ u m more quickly, but angular separation s increases more rapidly with $$\alpha $$ α and charge q. We compare our results with those for analogous black holes in General Relativity (GR) and also the formalism is applied to discuss the astrophysical consequences in the case of the supermassive black holes Sgr A* and M87*.

Charged traversable wormholes in f(R) gravity

2021 ◽  
pp. 2150098
Author(s):  
Nisha Godani ◽  
Gauranga C. Samanta
Keyword(s):  
Gravitational Lensing ◽  
Deflection Angle ◽  
Strong Field ◽  
Energy Condition ◽  
Weak Energy Condition ◽  
Exotic Matter ◽  
Field Limit ◽  
Traversable Wormholes ◽  
The Deflection Angle ◽  
Lensing Effect

This work is focused on the study of charged wormholes in the following two aspects: (i) to obtain exotic matter free effective charged wormhole solutions and (ii) to determine deflection angle for gravitational lensing effect. We have defined a novel redshift function, obtained wormhole solutions using the background of [Formula: see text] theory of gravity and found the regions obeying the weak energy condition. Further, the gravitational lensing effect is analyzed by determining the deflection angle in terms of strong field limit coefficients.

scholarly journals Weak Deflection Angle of some Classes of non-linear Electrodynamics Black Holes via Gauss-Bonnet Theorem

2020 ◽  
Author(s):  
Hasan El Moumni ◽  
Karima Masmar ◽  
Ali Övgün
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Weak Field ◽  
Leading Order ◽  
Plasma Medium ◽  
Non Linear ◽  
The Deflection Angle ◽  
Bonnet Theorem

In this paper, we study the gravitational lensing by some black hole classes within the non-linear electrodynamics in weak field limits. First, we calculate an optical geometry of the non-linear electrodynamics black hole then we use the Gauss-Bonnet theorem for finding deflection angle in weak field limits. The effect of non-linear electrodynamics on the deflection angle in leading order terms is studied. Furthermore, we discuss the effects of the plasma medium on the weak deflection angle.

scholarly journals Perturbative deflection angle, gravitational lensing in the strong field limit and the black hole shadow

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
Junji Jia ◽  
Ke Huang
Keyword(s):  
Gravitational Lensing ◽  
Deflection Angle ◽  
Strong Field ◽  
Distance Effect ◽  
Critical Value ◽  
Field Limit ◽  
Perturbative Method ◽  
The Deflection Angle ◽  
The Impact ◽  
Strong Field Limit

AbstractA perturbative method to compute the deflection angle of both timelike and null rays in arbitrary static and spherically symmetric spacetimes in the strong field limit is proposed. The result takes a quasi-series form of $$(1-b_c/b)$$ ( 1 - b c / b ) where b is the impact parameter and $$b_c$$ b c is its critical value, with coefficients of the series explicitly given. This result also naturally takes into account the finite distance effect of both the source and detector, and allows to solve the apparent angles of the relativistic images in a more precise way. From this, the BH angular shadow size is expressed as a simple formula containing metric functions and particle/photon sphere radius. The magnification of the relativistic images were shown to diverge at different values of the source-detector angular coordinate difference, depending on the relation between the source and detector distance from the lens. To verify all these results, we then applied them to the Hayward BH spacetime, concentrating on the effects of its charge parameter l and the asymptotic velocity v of the signal. The BH shadow size were found to decrease slightly as l increases to its critical value, and increase as v decreases from light speed. For the deflection angle and the magnification of the images however, both the increase of l and decrease of v will increase their values.

scholarly journals Strong gravitational lensing of a 4-dimensional Einstein–Gauss–Bonnet black hole in homogeneous plasma

2020 ◽  
Vol 29 (09) ◽  
pp. 2050065 ◽  
Author(s):  
Xing-Hua Jin ◽  
Yuan-Xing Gao ◽  
Dao-Jun Liu
Keyword(s):  
Gravitational Lensing ◽  
Deflection Angle ◽  
Strong Field ◽  
The Novel ◽  
Coupling Constant ◽  
Homogeneous Plasma ◽  
Strong Gravitational Lensing ◽  
Image Separation ◽  
Unmagnetized Plasma ◽  
Deflection Limit

We investigate the strong gravitational lensing of spherically symmetric black holes in the novel Einstein–Gauss–Bonnet (EGB) gravity surrounded by unmagnetized plasma medium. The deflection angle in the strong deflection limit in EGB spacetime with homogeneous plasma is derived. We find that both the coupling constant [Formula: see text] in the novel EGB gravity and the presence of plasma can affect the radius of photon sphere, strong field limit coefficient and other lensing observables significantly, while plasma has little effect on the angular image separation and the relative magnifications as [Formula: see text] and [Formula: see text], respectively.

Gravitational lensing by regular black holes surrounded by plasma

2017 ◽  
Vol 26 (05) ◽  
pp. 1741011 ◽  
Author(s):  
Ahmadjon Abdujabbarov ◽  
Bobir Toshmatov ◽  
Jan Schee ◽  
Zdeněk Stuchlík ◽  
Bobomurat Ahmedov
Keyword(s):  
Black Holes ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Field Approximation ◽  
Weak Field ◽  
Source Image ◽  
Primary Ring ◽  
Regular Black Hole ◽  
Regular Black Holes ◽  
The Deflection Angle

In the weak field approximation, we study the gravitational lensing near the regular Bardeen, Hayward and Ayon-Beato–Garcia (ABG) black holes surrounded by plasma. The exact expressions for the deflection angle of the photons due to the effect of the gravitational field and the plasma have been obtained. The analysis of the image source brightness magnification in the background spacetimes of (i) Bardeen, (ii) Hayward and (iii) ABG regular black holes have shown that the increase of the corresponding charge of regular black hole causes the increase in the magnification of the source image. In addition to the primary ring, one may observe the secondary ring with smaller magnification. The influence of the plasma with (i) constant and (ii) radial power law electron density to the magnification of the source image has been studied.

scholarly journals Weak deflection angle by asymptotically flat black holes in Horndeski theory using Gauss–Bonnet theorem

2020 ◽  
Vol 18 (01) ◽  
pp. 2150003
Author(s):  
Wajiha Javed ◽  
Jameela Abbas ◽  
Yashmitha Kumaran ◽  
Ali Övgün
Keyword(s):  
Black Holes ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Weak Field ◽  
Plasma Medium ◽  
Asymptotically Flat ◽  
Optical Geometry ◽  
Principal Objective ◽  
The Deflection Angle ◽  
Bonnet Theorem

The principal objective of this project is to investigate the gravitational lensing by asymptotically flat black holes in the framework of Horndeski theory in weak field limits. To achieve this objective, we utilize the Gauss–Bonnet theorem to the optical geometry of asymptotically flat black holes and apply the Gibbons–Werner technique to achieve the deflection angle of photons in weak field limits. Subsequently, we manifest the influence of plasma medium on deflection of photons by asymptotically flat black holes in the context of Horndeski theory. We also examine the graphical impact of deflection angle on asymptotically flat black holes in the background of Horndeski theory in plasma medium as well as non-plasma medium.

Strong gravitational lensing by Kerr–Newman-Nut-Quintessence black hole

2021 ◽  
Author(s):  
Niyaz Uddin Molla ◽  
Ujjal Debnath
Keyword(s):  
Black Hole ◽  
Equatorial Plane ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Null Geodesic ◽  
Kerr Black Hole ◽  
Eos Parameter ◽  
Strong Gravitational Lensing ◽  
Spin Parameter ◽  
The Deflection Angle

We investigate the strong gravitational lensing on equatorial plane as well as quasi-equatorial plane by the Kerr–Newman-Nut-Quintessence (KNNQ) black hole (BH) with the equation of state (EoS) parameter of the quintessence [Formula: see text] and the quintessence density [Formula: see text]. Our results show that the strong gravitational lensing in the KNNQ black hole space–time has some distinct behaviors from those in the backgrounds of the four dimension Kerr black hole. Also, we investigate the strong gravitational lensing on equatorial plane as well as quasi-equatorial plane by the KNNQ BH with the effects of Nut charge, spin parameter and quintessence parameter. First, we calculate the null geodesic equations using the Hamilton–Jacobi separation method. Then we investigate the equatorial lensing by KNNQ black hole. We obtain the deflection angle and deflection coefficients in the equatorial plane, which is affected by EoS parameter of the quintessence [Formula: see text], quintessence density [Formula: see text], Nut parameter [Formula: see text], spin parameter [Formula: see text] and quintessence parameter [Formula: see text] [Formula: see text]. Next, we discuss the lens equation and the observables in the equatorial plane. Finally, we investigate gravitational lensing by the KNNQ black hole in the quasi-equatorial plane. In this work, the quintessence density [Formula: see text], the EoS parameter of the quintessence [Formula: see text], Nut parameter [Formula: see text], spin parameter [Formula: see text] and quintessence parameter [Formula: see text] [Formula: see text] have significant effects on the strong gravitational lensing both in equatorial plane as well as quasi-equatorial plane.

scholarly journals Deriving Weak Deflection Angle by Black Holes or Wormholes using Gauss-Bonnet Theorem

2021 ◽  
Author(s):  
Yashmitha Kumaran ◽  
Ali Övgün
Keyword(s):  
Black Holes ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Weak Field ◽  
Plasma Medium ◽  
Asymptotically Flat ◽  
Finite Distance ◽  
Flat Spacetimes ◽  
The Deflection Angle ◽  
Bonnet Theorem

In this review, various researches on finding the bending angle of light deflected by a massive gravitating object which regard the Gauss-Bonnet theorem as the premise have been revised. Primarily, the Gibbons and Werner method is studied apropos of the gravitational lensing phenomenon in the weak field limits. Some exclusive instances are deliberated while calculating the deflection angle, beginning with the finite-distance corrections on non-asymptotically flat spacetimes. Effects of plasma medium is then inspected to observe its contribution to the deflection angle. Finally, the Jacobi metric is explored as an alternative method, only to arrive at similar results. All of the cases are probed in three constructs, one as a generic statement of explanation, one for black holes, and one for wormholes, so as to gain a perspective on every kind of influence.

Sign in / Sign up

Export Citation Format

Share Document