Exploring the shadow of a rotating charged ModMax black hole

The research presented in this paper discusses the impact that the parameters of charge(Q)and screening factor(γ)have on properties of the horizon and silhouette of rotating charged Mod Max black holes which were reviewed in[Eur.Phys.J.C(2022)82:1155]recently,building upon previous findings in the field.Furthermore,the study explores the behavior of null geodesics,which can help us better understand the apparent shape of the black hole’s silhouette,as well as the distortion parameter and approximate radii of the silhouette that are influenced by the aforementioned parameters,and there are some values of parameter Q which corresponds to data from the Event Horizon Telescope(EHT).Notably,we explore the distortion parameter and approximate radii of the silhouette,revealing that while an increase inγleads to a growth in silhouette radius(Rs),it simultaneously reduces the distortion rate(δs).Conversely,heightened Q charge results in a reduction of Rsaccompanied by an increase inδs.Lastly,the paper analyzes the effects of the black hole’s parameters on the effective potential and energy emission:the peak value of the energy emission rate experiences a decrease as the screening factor(γ)increases,while it increases with higher values of the charge parameter(Q).

Shadow and weak gravitational lensing for Ellis-Bronnikov wormhole

In this study,we investigated the gravitational weak lensing and shadow of the Ellis-Bronnikov wormhole.First,we studied the photon motion in a plasma medium and a wormhole shadow.It was shown that the radius of the photon sphere of the Ellis-Bronnikov wormhole and the size of the wormhole shadow become larger under the influence of the parameter a.The upper limit of the parameter a in the Ellis-Bronnikov wormhole spacetime was obtained.Second,we investigated the weak gravitational lensing for the Ellis-Bronnikov wormhole and calculated the deflection angle for uniform and non uniform plasma cases.The value of the deflection angle for uniform plasma increased with the increase in plasma parameter value,and vice versa for non uniform plasma.We found that,under the influence of the parameter a,the values of the deflection angles for two cases decreased.Finally,we investigated the magnification of image brightness using the deflection angle of the light rays around the wormhole in the EllisBronnikov theory.

Weak deflection angle and shadow cast by the charged-Kiselev black hole with cloud of strings in plasma

In this study,the gravitational deflection angle of photons in the weak field limit(or the weak deflection angle)and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole(BH)in the string cloud background are investigated.The influences of the BH charge Q,quintessence parameterγ,and string cloud parameter a on the weak deflection angle are studied using the Gauss-Bonnet theorem.in addition to studying the influences on the radius of photon spheres and size of the BH shadow in the spacetime geometry of the chargedKiselev BH in string clouds.Moreover,we study the effects of plasma(uniform and non-uniform)on the weak deflection angle and shadow cast by the charged-Kiselev BH surrounded by the clouds of strings.In the presence of a uniform/nonuniform plasma medium,an increase in the string cloud parameter a increases the deflection angleα.In contrast,a decrease in the BH charge Q decreases the deflection angle.Further,we observe that an increase in the BH charge Q causes a decrease in the size of the shadow of the BH.We notice that,with an increase in the values of the parametersγand a,the size of the BH shadow increases,and therefore,the intensity of the gravitational field around the charged-Kiselev BH in string clouds increases.Thus,the gravitational field of the charged-Kiselev BH in the string cloud background is stronger than the field produced by the pure Reissner-Nordstrom BH.Moreover,we use the data released by the Event Horizon Telescope(EHT)collaboration,for the supermassive BHs M87*and Sgr A*,to obtain constraints on the values of the parametersγand a.

Particle dynamics,black hole shadow and weak gravitational lensing in the f(Q)theory of gravity

We study the particle dynamics around a black hole(BH)in f(Q)gravity.First,we investigate the influence of the parameters of f(Q)gravity on the horizon structure of the BH,photon orbits and the radius of the innermost stable circular orbit(ISCO)of massive particles.We further study the effects of the parameters of f(Q)gravity on the shadow cast by the BH.Moreover,we consider weak gravitational lensing using the general method,where we also explore the deflection angle of light rays around the BH in f(Q)gravity in uniform and nonuniform plasma mediums.

Probing Horava-Lifshitz gravity using particle and photon dynamics in the presence of plasma

We study the particle motion around a black hole(BH)in Horava-Lifshitz(HL)gravity with the Kehagias-Sfetsos(KS)parameter.First,the innermost stable circular orbit(ISCO)is obtained for massive particles around the BH in HL gravity.We find that the radii of the ISCOs decrease as the KS parameter decreases,meaning that the parameterΩcauses the orbits of particles to move inward with respect to that of the Schwarzschild BH case.Then,the optical properties of a KS BH are studied in detail,that is,the BH shadow and gravitational weak lensing.We demonstrate that the size of the BH shadow decreases under the influence of the KS parameter.

Quantum effects on the black hole shadow and deflection angle in the presence of plasma

In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present the modifications in the shadow radius of the RGI BH.To this end,we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media.Importantly,owing to the plasma media,we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified.This,in turn,changes and modifies the expression for the intensity observed far away from the BH.Finally,we obtain the shadow images for the RGI BH for different plasma models.Although quantum effects change the background geometry,such effects are minimal,and practically detecting these effects using the current technology based on supermassive BH shadows is impossible.The parameterΩencodes the quantum effects,and in principle,one expects such quantum effects to play significant roles only for very small BHs.However,the effects of plasma media can play an important role in the optical appearance of BHs,as they affect and modify the equations of motion.

Photon motion and weak gravitational lensing in black-bounce spacetime

The effect of spacetime curvature on photon motion may offer an opportunity to propose new tests on gravity theories.In this study,we investigate and focus on the massless(photon)particle motion around blackbounce gravity.We analyze the horizon structure around a gravitational compact object described by black-bounce spacetime.The photon motion and the effect of gravitational weak lensing in vacuum and plasma are discussed,and the shadow radius of the compact object is also studied in black-bounce spacetime.Additionally,the magnification of the image is studied using the deflection angle of light rays.

Shadows and gravitational weak lensing by the Schwarzschild black hole in the string cloud background with quintessential field

In this study,we observe that,in the presence of the string cloud parameter a and the quintessence parameterγ,with the equation of state parameter,ω_(q) = -2/3the radius of the shadow of the Schwarzschild black hole increases as compared with that in the pure Schwarzschild black hole case.The existence of both quintessential dark energy and the cloud of strings increases the shadow size;hence,the strength of the gravitational field around the Schwarzschild black hole increases.Using the data collected by the Event Horizon Telescope(EHT)collaboration for M87*and Sgr A*,we obtain upper bounds on the values of a andγ.Further,we see the effects of a andγon the rate of emission energy for the Schwarzschild black hole.We notice that the rate of emission energy is higher in the presence of clouds of strings and quintessence.Moreover,we study the weak deflection angle using the Gauss-Bonnet theorem.We show the influence of a andγon the weak deflection angle.We notice that both a andγincrease the deflection angleα.