Thermal, topological, and scattering effects of an AdS charged black hole with an antisymmetric tensor background

Unification of gravity with other interactions, achieving the ultimate framework of quantum gravity, and fundamental problems in particle physics and cosmology motivate to consider extra spatial dimensions. The impact of these extra dimensions on the modified theories of gravity has attracted a lot of attention. One way to examine how extra dimensions affect the modified gravitational theories is to analytically investigate astrophysical phenomena, such as black hole shadows. In this study, we aim to investigate the behavior of the shadow shapes of higher-dimensional charged black hole solutions including asymptotically locally flat (ALF) and asymptotically locally AdS (ALAdS) in Einstein–Horndeski–Maxwell (EHM) gravitational theory. We utilize the Hamilton–Jacobi method to find photon orbits around these black holes as well as the Carter approach to formulate the geodesic equations. We examine how extra dimensions, negative cosmological constant, electric charge, and coupling constants of the EHM gravity affect the shadow size of the black hole. Then, we constrain these parameters by comparing the shadow radius of these black holes with the shadow size of M87* supermassive black hole captured by the Event Horizon Telescope (EHT) collaborations. We discover that generally the presence of extra dimensions within the EHM gravity results in reducing the shadow size of higher-dimensional ALF and ALAdS charged black holes, whereas the impact of electric charge on the shadow of these black holes is suppressible. Interestingly, we observe that decreasing the negative cosmological constant, i.e., increasing its absolute value, leads to increase the shadow size of the ALAdS charged higher-dimensional black hole in the EHM gravity. Surprisingly, based on the constraints from EHT observations, we discover that only the shadow size of the four dimensional ALF charged black hole lies in the confidence levels of EHT data, whereas owing to the presence of the negative cosmological constant, the shadow radius of the four, five, and seven dimensional ALAdS charged black holes lie within the EHT data confidence levels.

Optical features of rotating quintessential charged black holes in de-Sitter spacetime

In this paper, we study the particle dynamics, shadow, and optical appearance of charged black holes (BHs) in bumblebee gravity. Firstly, we find that the Lorentz-violation parameter $l$ and charge parameter $Q$ have opposite effects on the peak of the effective potential by analyzing timelike geodesics, and the radius of the innermost stable circular orbit (ISCO) decreases as the BH parameters $l$ and $Q$ increase. We also explore the behaviors of particle energy, angular momentum, and Keplerian frequency. Secondly, for null geodesics, both the photon sphere radius and the shadow radius decrease with increasing $l$ and $Q$, and are consistently smaller than those of the Reissner–Nordström black hole (RNBH) and Schwarzschild-like BH. And based on observational data reported by the Event Horizon Telescope (EHT) Collaboration, we constrain the parameters $l$ and $Q$ by using the shadow radius data of Sgr A*. Thirdly, we explore the observation characteristics of charged BHs under three thin disk accretion models. The results show that, compared to RNBH, the increase of $l$ leads to a greater thickness of the photon rings and lensed rings. However, due to their extremely narrow ranges, the contributions are small, and the observed intensities are mainly contributed by the direct emissions. Moreover, when the parameter $l$ is fixed, the peaks of the observed intensities of rings decrease with increasing $Q$ for the same emission model, and it is always lower than the corresponding value for Schwarzschild-like BH. These findings contribute to distinguishing bumblebee charged black holes (BCBHs) from other types of BHs based on their optical appearance.

In this paper, we report on exact charged black hole solutions in symmergent gravity with Maxwell field. Symmergent gravity induces the gravitational constant G, quadratic curvature coefficient , and the vacuum energy from the flat spacetime matter loops. In the limit in which all fields are degenerate in mass, the vacuum energy can be expressed in terms of G and . We parametrize deviation from this limit by a parameter such that the black hole spacetime is de Sitter (dS) for and anti-de Sitter (AdS) for . In our analysis, we study horizon formation, shadow cast and gravitational lensing as functions of the black hole charge, and find that there is an upper bound on the charge. At relatively low values of charge, applicable to astronomical black holes, we determine constraints on and using the Event Horizon Telescope (EHT) data from Sgr. A* and M87*. We apply these constraints to reveal how the shadow radius behaves as the observer distance varies. It is revealed that black hole charge directly influences the shadow silhouette, but the symmergent parameters have a tenuous effect. We also explored the weak field regime by using the Gauss–Bonnet theorem to study the weak deflection angle caused by the M87* black hole. We have found that impact parameters comparable to the actual distance D = 16.8 Mpc show the potential detectability of such an angle through advanced astronomical telescopes. Overall, our results provide new insights into the behavior of charged black holes in the context of symmergent gravity and offer a new way to test these theories against observational data.

In this study, we comprehensively investigated charged AdS black holes surrounded by a distinct form of dark matter. In particular, we focused on key elements including the Hawking temperature, quasi-normal modes (QNMs), emission rate, and shadow. We first calculated the Hawking temperature, thereby identifying critical values such as the critical radius and maximum temperature of the black hole, essential for determining its phase transition. Further analysis focused on the QNMs of charged AdS black holes immersed in perfect fluid dark matter (PFDM) within the massless scalar field paradigm. Employing the Wentzel-Kramers-Brillouin (WKB) method, we accurately derived the frequencies of these QNMs. Additionally, we conducted a meticulous assessment of how the intensity of the PFDM parameter α influences the partial absorption cross sections of the black hole, along with a detailed study of the frequency variation of the energy emission rate. The pivotal role of geodesics in understanding astrophysical black hole characteristics is highlighted. Specifically, we examined the influence of the dark matter parameter on photon evolution by computing the shadow radius of the black hole. Our findings distinctly demonstrate the significant impact of the PFDM parameter α on the boundaries of this shadow, providing crucial insights into its features and interactions. We also provide profound insights into the intricate dynamics between a charged AdS black hole, novel dark matter, and various physical phenomena, elucidating their interplay and contributing valuable knowledge to the understanding of these cosmic entities.

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 parameter γ, 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 charged-Kiselev 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 angle α. 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 parameters γ and 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 parameters γ and a.

A Kerr-Sen-like black hole solution appears in the Einstein-bumblebee theory of gravity. The solution contains contains a Lorentz violating parameter in an explicit manner. We study the null geodesics in the background of this Kerr-Sen-like black hole surrounded by a dispersive medium like plasma. We investigate the effect of the charge of the black hole, the Lorentz violation parameter, and the plasma parameter on the photon orbits with the evaluation of the effective potential in the presence of both the Lorentz violation parameter and the plasma parameter. We also study the influence of the Lorentz violation parameter and plasma parameter on the emission of energy from the black hole due to thermal radiation. Besides, we compute the angle of deflection of massless particles with weak-field approximation in this generalized situation and examine how it varies with the Lorentz violation parameter in presence of plasma. Constraining the parameters of this Lorentz violating Kerr-Sen-like black hole is also attempted here with the result obtained from the observations of the Event Horizon Telescope (EHT) collaboration.

Background: Little data is available for the pygmy dipole resonance (PDR) in axially deformed nuclei. Photon-scattering experiments are complicated by high level densities in the PDR region and the small energy difference of transitions to the ground state and to excited states.Purpose: We report on an experimental study of the low-energy dipole strength distribution of the well-deformed nucleus $^{164}\mathrm{Dy}$ between 4.0--7.7 MeV.Methods: The low-lying photoresponse of $^{164}\mathrm{Dy}$ has been investigated using the method of nuclear resonance fluorescence using a quasimonochromatic linearly polarized $\ensuremath{\gamma}$-ray beam in the energy range of 4.0--7.7 MeV in steps of 0.2 MeV.Results: For excitation energies between 4 MeV and 5 MeV, sufficiently low level densities allow for the identification of individual states, including level energies, reduced transition widths and branching ratios. Energy-averaged mean decay branching ratios, mean population ratios and partial absorption cross sections were determined above 5 MeV up to the neutron-separation threshold at 7.7 MeV. A Lorentzian-shaped enhancement of the partial photo absorption cross section followed by decays back to the ground-state band is found at 6.10(5) MeV with a width of 0.77(23) MeV. A comparison with results from complementary measurements is performed using the framework of the statistical model.Conclusions: The experimental results for the mean population ratios deviate systematically from the statistical model simulation by 30(6)%. However, they are in agreement within one standard deviation of the simulation.

The low energy absorption cross section and the decay rate of the stationary Axisymmetric Einstein–Maxwell Dilaton Axion black hole for massless scalar particles is calculated analytically. It is shown that the partial absorption cross section increases as the rotating parameter a and the absolute value of the dilaton D decreases. It is also shown that the partial absorption cross section is not always positive due to superradiance factor ω–mΩ. However, the decay rate of this black hole is always positive.

Black hole evaporation process and Tangherlini–Reissner–Nordström black holes shadow

In this work, we study the thermodynamic topology of a static, a charged static, and a charged rotating black hole in f(R) gravity. For charged static black holes, we work in two different ensembles: the fixed charge (q) ensemble and fixed potential (ϕ) ensemble. For charged rotating black holes, four different types of ensembles are considered: fixed (q, J), fixed (ϕ, J), fixed (q, Ω), and fixed (ϕ, Ω) ensemble, where J and Ω denote the angular momentum and the angular frequency, respectively. Using the generalized off-shell free energy method, where the black holes are treated as topological defects in their thermodynamic spaces, we investigate the local and global topologies of these black holes via the computation of winding numbers at these defects. For the static black hole we work in three models. We find that the topological charge for a static black hole is always −1 regardless of the values of the thermodynamic parameters and the choice of f(R) model. For a charged static black hole, in the fixed charge ensemble, the topological charge is found to be zero. Contrastingly, in the fixed ϕ ensemble, the topological charge is found to be −1. For charged static black holes, in both the ensembles, the topological charge is observed to be independent of the thermodynamic parameters. For charged rotating black holes, in the fixed (q, J) ensemble, the topological charge is found to be 1. In the fixed (ϕ, J) ensemble, we find the topological charge to be 1. In the case of the fixed (q, Ω) ensemble, the topological charge is 1 or 0 depending on the value of the scalar curvature (R). In the fixed (Ω, ϕ) ensemble, the topological charge is −1, 0, or 1 depending on the values of R, Ω, and ϕ. Therefore, we conclude that the thermodynamic topologies of the charged static black hole and charged rotating black hole are influenced by the choice of ensemble. In addition, the thermodynamic topology of the charged rotating black hole also depends on the thermodynamic parameters.

Matter accretion onto charged black holes in symmergent gravity

Testing gravitational lensing effects by supermassive massive black holes with superstring theory metric: Astrophysical implications and EHT constraints

Charged Lifshitz black holes for the Einstein-Proca-Maxwell system with a negative cosmological constant in arbitrary dimension D are known only if the dynamical critical exponent is fixed as z = 2(D − 2). In the present work, we show that these configurations can be extended to much more general charged black holes which in addition exist for any value of the dynamical exponent z > 1 by considering a nonlinear electrodynamics instead of the Maxwell theory. More precisely, we introduce a two-parametric nonlinear electrodynamics defined in the more general, but less known, so-called ( $ \mathcal{H} $ , P )-formalism and obtain a family of charged black hole solutions depending on two parameters. We also remark that the value of the dynamical exponent z = D − 2 turns out to be critical in the sense that it yields asymptotically Lifshitz black holes with logarithmic decay supported by a particular logarithmic electrodynamics. All these configurations include extremal Lifshitz black holes. Charged topological Lifshitz black holes are also shown to emerge by slightly generalizing the proposed electrodynamics.

The recent Event Horizon Telescope (EHT) observations of the M87* have led to a surge of interest in studying the shadow of black holes. Besides, investigation of time evolution and lifetime of black holes helps us to veto/restrict some theoretical models in gravitating systems. Motivated by such exciting properties, we study optical features of black holes, such as the shadow geometrical shape and the energy emission rate in modified gravity. We consider a charged AdS black hole in dRGT massive gravity and look for criteria to restrict the free parameters of the theory. The main goal of this paper is to compare the shadow of the mentioned black hole in a rotating case with the EHT data to obtain the allowed regions of the model parameters. Therefore, we employ the Newman-Janis algorithm to build the rotating counterpart of static solution in dRGT massive gravity. We also calculate the energy emission rate for the rotating case and discuss how the rotation factor and other parameters affect the emission of particles around the black holes.