In this work, we observe that in the presence of the string cloud parameter $a$ and the quintessence parameter $\gamma$, with the equation of state parameter $\omega_q={-2}/{3}$ the radius of the shadow of the Schwarzschild black hole increases as compared with the pure Schwarzschild black hole case. The existence of both quintessential dark energy and cloud of strings magnify the shadow size and 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 the M87* and Sgr A*, we obtain upper bounds on the values of the parameters $a$ and $\gamma$. Further, we see the effects of the parameters $a$ and $\gamma$ on 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 string and quintessence. Moreover, we study the weak deflection angle using the Gauss-Bonnet theorem. We show the influence of the cloud of string parameter $a$ and the quintessential parameter $\gamma$ on the weak deflection angle. We notice that both the parameters $a$ and $\gamma$ increase the deflection angle $\alpha$.

In this paper, we have studied the particle dynamics, gravitational lensing and energy processes around the black hole (BH) in Kalb–Ramond (KR) gravity. The motion of particles is considered with parameters in KR BH and investigated for massive and massless particles. From this work, we have got the horizon structure, photon orbit of photon and ISCO (inner stable circular orbit) of a mass particle with parameters in KR gravity. The effective potential is also studied for the massless and mass particles. Additionally, we tested energy extracted from BH using the BSW (Banados–Silk–West) method and derived the expression of center mass-energy in KR gravity. The impact of the model parameters $$\gamma $$ γ and $$\lambda $$ λ is checked to study the size of the BH shadow in the KR gravity. Gravitational weak lensing has been explored using the general method and the derived deflection angle of light rays around the BH for the plasma of various concentration distributions. The magnification of brightness is obtained using the angle of deflection of the light rays.

In this work, the gravitational deflection angle of photon 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 influence of the BH charge $Q$, the quintessential parameter $\gamma$ and the string cloud parameter $a$ is studied on the weak deflection angle using the Gauss-Bonnet theorem, on the radius of photon spheres and on the size of the BH shadow in the spacetime geometry of the charged-Kiselev BH in string clouds. Moreover, we study the effects of plasma (uniform and non-uniform) on the weak deflection angle and on the shadow cast by the charged-Kiselev BH surrounded by the clouds of strings. In the presence of uniform/nonuniform plasma medium, increase in the cloud of string parameter $a$, increases the deflection angle $\alpha$. On the other hand decrease in the BH charge $Q$, decreases the deflection angle. Further we observe that an increase of the BH charge $Q$ causes a decrease in the size of the shadow of the BH. We notice that with increase in the values of the parameters $\gamma$ and $a$, the size of the BH shadow also 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 string cloud background would be 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 parameters $\gamma$ and $a$.

In this article, we find the possibility of generalized wormhole formation in the galactic halo due to dark matter using observational data within the matter coupling gravity formalism. Keeping this as a target, we specifically employ f(R, T) gravity with (i) a variational approach concerning the metric, and (ii) the anisotropic source of matter. To understand the features of the wormholes, we thoroughly calculated and analyzed the energy conditions under f(R, T) gravity. We discuss the second embedded wormhole solution, known as the generalized Ellis–Bronnikov spacetime (ultrastatic wormhole model), in terms of the tortoise coordinate. Thereafter we generate and compare different wormhole solutions depending on the parametric values. In the second part of our investigation, we presented dark matter halos and provided interesting features by considering a couple of profiles. For the dark matter halos models, we particularly use the observational data of the M87 galaxy and the Milky Way galaxy.

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In this paper, we investigate the accelerated expansion of the Universe in the context of [Formula: see text] modified theory of gravity, where [Formula: see text] is a non-metricity scalar which characterizes the gravitational interaction by using parametrization of the deceleration parameter [Formula: see text] with [Formula: see text], where [Formula: see text] and [Formula: see text] are free parameters constrained by the 57 points of [Formula: see text] datasets, 1048 points of Pantheon, 10 points from Baryon Acoustic Oscillations (BAO) datasets and the shift parameters from Planck 2018 of Cosmic Microwave Background (CMB). In the purpose of validating our model, we proceed by the [Formula: see text] diagnostic and the energy conditions. Later we discussed how our model statistically supports [Formula: see text]CDM using [Formula: see text] criterion analysis.

We investigate the thermodynamic properties and Joule–Thomson expansion for conical or BTZ-like black holes. To analyze the thermal stability, we discuss the temperature and thermal stability relative to the horizon radius for different values of model parameters $$\beta _0$$ β 0 and $$\alpha _2$$ α 2 . Moreover, we analyze thermodynamical geometries like Ruppeiner, Weinhold and Hendi Panahiyah Eslam Momennia formulation and calculate respective scalar curvatures for BTZ-like black holes. Interestingly, the black holes have no singularity in some cases, i.e., completely regular. We obtain the inversion temperatures and inversion curves and investigate the similarities and differences between van der Waals and charged fluids. To discuss this expansion, we use a BTZ-like black hole. Further, we establish the position of the inversion point versus different values of mass $$\mu $$ μ , and the parameters $$\beta _0$$ β 0 and $$\alpha _2$$ α 2 for such a BTZ-like black hole. The Joule–Thomson coefficient $$\mu $$ μ at this point disappears. A crucial trait upon which we relied to inspect the sign of quantity $$\mu $$ μ to get the cooling-heating areas. We also investigate the energy emission depending upon the frequency $$\omega $$ ω .

This article explores the wormhole geometry in the background of symmetric teleparallel gravity or f () gravity, where  is the non-metricity term, and definite subject for the gravitational interaction. All the energy conditions are investigated for two different generic shape functions. The presence of exotic matter is confirmed due to the violation of the energy conditions. The epicyclic orbits of test particles around wormhole throat for the considered models are discussed. Twin peak Quasi-periodic oscillations are calculated and presented with the required behavior. We also explore the physical characteristics and stable configuration of thin-shell developed from the matching of inner obtained solution of wormhole geometry and outer black hole solution in f () gravity. The stability of shell is discussed by using the speed of sound parameter for both choices of shape functions, i.e., 𝜷 1 (D) and 𝜷 2 (D). It is found that the position of event horizon does not change for different values of the physical parameter for the choice of 𝜷 1 (D) while it changes for 𝜷 2 (D). We explore the proper length, shell energy and entropy of the developed structure for different values of physical parameters.