Polymer black hole surrounded by quintessence

We investigate strong gravitational lensing by two static black hole models (Model-1 and Model-2) within the Effective Quantum Gravity (EQG) framework, characterized by mass M and parameter ζ. For ζ=0, they reduce to the Schwarzschild solution, and depending on the parameters, they describe black holes with an event and Cauchy horizon (Model-1), a single horizon (Model-2), or no horizons. Using supermassive black holes (SMBHs), Sgr A* and M87*, as lenses and integrating theoretical predictions with recent Event Horizon Telescope (EHT) data, we identify significant differences in lensing signatures due to quantum corrections. For Model-1, the deviations of the lensing observables |δθ∞| of black holes in EQG from Schwarzschild black hole, for SMBHs Sgr A* and M87*, can reach as much as 1.75μas and 1.32μas, while |δs| is about 30.12 nas for Sgr A* and 22.63 nas for M87*. The flux ratio of the first image to all subsequent packed images indicates that EQG black hole images are brighter than their Schwarzschild counterparts, with a deviation in the brightness ratio |δrmag| reaching up to 2.02. The time delays between the second and first images, denoted |δT2,1|, exhibit substantial deviations from the GR counterpart, reaching up to 1.53 min for Sgr A* and 1159.9 min for M87*. The Event Horizon Telescope (EHT) constraint on θsh of Sgr A* and M87*, within the 1-σ region, limits the parameter ζ. Our analysis concludes that EQG black holes are consistent with the EHT observations within a finite parameter space.

In this study, in the framework of the Hamilton approach, the quantum gravity effect on Hawking temperature, on the specific heat capacity, and on the stability conditions of the charged de Rham, Gabadadze, and Tolley (dRGT) black hole are investigated by using the tunneling processes of both charged massive scalar and Dirac particles. It is shown that quantum corrected Hawking temperature depends not only on the black hole properties but also on the properties of the tunnelling particles. It is also observed that quantum corrected Hawking temperature is lower than that of the standard Hawking temperature. Also, the specific heat capacity and the local stability conditions of the black hole are discussed in the context of the tunneling processes of both charged massive scalar and Dirac particles in the presence of quantum gravity effect. It is observed that the black hole might undergo second-type phase transitions to become stable during the tunneling processes of both scalar and Dirac particles. However, in the absence of the quantum gravity effect, the black hole might undergo the both first-type and second-type phase transitions to become stable.

<p><strong>The future of theoretical physics is unclear. Two large areas that fall under the umbrella of theoretical physics are cosmology and quantum gravity. Modern cosmology is relatively a much younger field than quantum gravity, and both of these fields require further developments of general relativity. In this thesis we do not hope to resolve the problems facing modern cosmology or theories of quantum gravity. Rather, we will conduct original research into aspects of general relativity that may be used in the future to aid the development and testing of theories of cosmology and quantum gravity.</strong></p><p>It is our view that the largest problem facing astrophysics and cosmology stem from the existence of the dark sector of the Universe. The implication here being that more than ninety percent of the energy density of the Universe is “missing in action” and seemingly consists of dark energy and dark matter. Furthermore, it is apparent that there exist conceptual flaws in our understanding of observational concepts such as expansion versus motion and observer biases. To this end, we investigate the standard spacetime metric used in cosmology, the Friedmann–Lemaˆıtre-Roberston–Walker (FLRW) metric in a peculiar coordinate system — the Painlev´e–Gullstrand coordinates. In this coordinate system (slicing), space is no longer expanding, rather, the galaxies are receding from each other. We hope this will aid in the understanding of expansion, motion, curvature, and observer bias with future work. We further investigate the possibility of black holes in cosmology being directly coupled to the accelerated expansion of the Universe — in other words, black holes as a source for dark energy. However, we show that this is highly implausible.</p><p>Relatively recently it has been postulated that the near black hole horizon limit may be a regime where quantum gravity effects become relevant i.e., quantum gravity may not be restricted to near the Planck scale. We investigate a curious model of black and white holes that shows how one may transition into the other over a finite period of time. This is research conducted in the near horizon limit of the Schwarzschild black hole. We introduce a time dependent function into the usual Schwarzschild black hole spacetime (leaving this new spacetime not a simple coordinate transformed version of the original). This function allows the black hole to transition into a white hole. Importantly, the action for this transition can be shown to be zero, meaning it can be added to the Feynman path integral at no cost.</p><p>Finally, we move to investigating the black hole memory effect. During the last decade, there has been an interesting connection made between the Bondi– Metzner–Sachs (BMS) group — an infinite dimensional group of symmetries found at null infinity — and the gravitational memory effect. In particular, it was shown that the passage of a gravitational wave that alters a Schwarzschild black hole is seen as a supertranslation of the spacetime at null infinity. We extend these calculations to the Kerr and Kerr–Newman black holes. Hence, showing that there may be a way to verify the abstract mathematical ideas predicated on the BMS group by detection of the memory effect in future observations.</p><p>It is our hope that when future gravitational wave detectors such as the laser-interferometer-space-antenna (LISA) are launched, research conducted in this thesis may shed light on how the memory may relate to black holes in their asymptotic & near horizon limits to aid our understanding of the nature of quantum gravity.</p>

In this paper, we study the effect of quantum gravity on the thermal property of the Reissner–Nordström–NUT–Kiselev–Rastall (RN-NUT-KR) black hole in the context of the tunneling process of scalar/fermion particles. We analyze the tunneling radiation by using the electromagnetic Klein–Gordon equation and the electromagnetic Dirac equation generalized with the modified fundamental commutation relations. We solve these equations by the Hamilton–Jacobi ansatz with the semiclassical WKB approximation. The modified Hawking temperature of the black hole depends not only on the black hole background but also on the emitted particle’s quantum numbers. The quintessence and Rastall parameters increase the Hawking temperature for small black holes, while the quantum gravity effect decelerates the temperature increasing in the evaporation process and causes the black holes to remain as remnants. We also compute the modified heat capacity and modified Gibbs free energy and investigate the thermodynamic stability conditions and phase transitions.

This work presents a comprehensive investigation of the gravitational phenomena that correspond to a non–commutative charged black hole, by incorporating non–commutative geometry through a (r, θ) Moyal twist. We derive the deformed metric up to the second order of non–commutative parameter Θ, utilizing the Seiberg–Witten map for Reissner–Nordstr¨om black hole. We explore how non–commutativity modifies key thermodynamic properties, such as the Hawking temperature and heat capacity, and the existence of a remnant mass at the final stage of the evaporation. Additionally, the study of Hawking radiation for bosonic and fermionic particles is discussed. Applying a perturbative method, scalar quasinormal modes are analyzed numerically. Furthermore, null geodesics and photon sphere stability are explored via curvature and topological methods. The shadow radius and deflection angle are computed to understand observational signatures. Lensing observables are compared to Event Horizon Telescope (EHT) observations to provide probable constraints on the non-commutativity parameter. This study bridges theoretical predictions with astrophysical observations, offering insights into quantum gravity effects on black hole physics.

A black hole greybody factor is the quantum quantity of a black hole. It is the fraction of Hawking radiation that can reach spatial infinity. The greybody factor may contain the necessary information to support the theory of quantum gravity. An understanding of the greybody factor helps us gain insight, not only into the nature of the black hole itself, but also into the theory of quantum gravity, which is currently being developed via numerous attempts. In this paper, we calculate the bound on the greybody factor for scalar field emitted from black holes in dRGT massive gravity. The bound on the reflection probability is also determined. Moreover, the effects of massive gravity on the greybody factors are explored. The results show that the bound on the greybody factor for the dRGT black holes is less than the bound for the Schwarzschild-de-Sitter black hole. The Hawking temperature is also calculated, both in the dRGT case and in the Schwarzschild-de-Sitter case. It is found that the Hawking temperature of the dRGT black hole is higher than that of the Schwarzschild-de-Sitter black hole. The increase in the Hawking temperature probably results from the mass of graviton. Finally, the black hole entropy is also determined. We found that the entropy of the Schwarzschild-de-Sitter black hole is more than the entropy of the dRGT black hole.

A mathematically consistent rotating black hole model in loop quantum gravity (LQG) is yet lacking. The scarcity of rotating black hole solutions in LQG substantially hampers the development of testing LQG from observations, e.g., from the Event Horizon Telescope (EHT) observations. The EHT observation revealed event horizon-scale images of the supermassive black holes Sgr A* and M87*. The EHT results are consistent with the shadow of a Kerr black hole of general relativity. We present LQG-motivated rotating black hole (LMRBH) spacetimes, which are regular everywhere and asymptotically encompass the Kerr black hole as a particular case. The LMRBH metric describes a multi-horizon black hole in the sense that it can admit up to three horizons, such that an extremal LMRBH, unlike the Kerr black hole, refers to a black hole with angular momentum a > M. The metric, depending on the parameters, describes (1) black holes with only one horizon (BH-I), (2) black holes with an event horizon and a Cauchy horizon (BH-II), (3) black holes with three horizons (BH-III), or (4) no-horizon spacetime, which we show is almost ruled out by EHT observations. We constrain the LQG parameter with the aid of the EHT shadow observational results of M87* and Sgr A*, respectively, for inclination angles of 17° and 50°. In particular, the VLTI bound for Sgr A*, δ ∈ (−0.17, 0.01), constrains the parameters (a, l) such that for 0 < l ≤ 0.347851M (l ≤ 2 × 106 km), the allowed range of a is (0, 1.0307M). Together with the EHT bounds of Sgr A* and M87* observables, our analysis concludes that a substantial part of BH-I and BH-II parameter space agrees with the EHT results of M87* and Sgr A*. While the EHT M87* results totally rule out BH-III, but not that by Sgr A*.

We present a study on quantum gravity effects on the shadow of a rotating black hole (BH) obtained in the setting of the asymptotically safe gravity. The rotating metric, which results from a static regular one recently presented in the literature, is generated by using the generalized Newman-Janis algorithm. The novelty of the static regular metric lies in the fact that it is the outcome of an effective Lagrangian which describes dust whose spherically symmetric collapse is non-singular as a consequence of the antiscreening character of gravity at small distances. The effective Lagrangian includes a multiplicative coupling, denoted as χ, with the Lagrangian of the collapsing fluid. The resulting exterior metric for large radii depends on a free parameter ξ which captures the quantum gravity effects. The form of the coupling χ and its connection with the quantum parameter ξ are determined by the running of the Newton coupling G(k) along a renormalization group trajectory that stops at the ultraviolet non-gaussian fixed point of the asymptotic safety theory for quantum gravity. Varying both the spin parameter a⋆ and the quantum parameter ξ, we explore the quantum gravity effects on several astronomical observables used to describe the morphology of the shadow cast by rotating BHs. In order to obtain constraints on the parameter ξ, we confront our results with the recent Event Horizon Telescope (EHT) observations of the shadows of the supermassive BHs M87∗ and Sgr A∗. We find that the ranges of variation of all the studied shadow observables fall entirely within the ranges determined by the EHT collaboration. We then conclude that the current astronomical data do not rule out the renormalization group improved rotating BH.

Black hole thermodynamics establishes a deep and satisfying link to gravity, thermodynamics, and quantum theory. And, the thermodynamic property of black hole is essentially a quantum feature of gravity. In this paper, in order to study the influence of the quantum gravity effect on the quantum properties of black hole, we study the thermodynamics and its quantum correction to a non-commutative black hole. First of all, the temperature of the non-commutative Schwarichild black hole is calculated by using three different methods: surface gravity, tunneling effects and the first law of black hole thermodynamics. It is found that the same hole temperature is obtained by means of the surface gravity and tunneling effects. However, by using the first law of black hole thermodynamics, different results are derived from the first two methods. Therefore, we incline to the result obtained by surface gravity and tunneling effects, and the temperature obtained by the thermodynamic law needs modifying. That is, for the non-commutative black hole, there is a contradiction to the first law of thermodynamics. To calculate the temperature and other thermodynamic quantities for the non-commutative Schwarichild black hole, we use the corrected first law of black hole thermodynamics proposed in the literature. It is found that the black hole temperature derived by the corrected first law is the same as the temperature obtained by the surface gravity and the tunneling model, and the black hole entropy still follows Beckenstein-Hawking area law. Also, the heat capacity of the black hole is obtained and analyzed. It is seen that when the horizon radius and non-commutative parameter satisfy the particular conditions, the heat capacity is positive and the non-commutative black holes are thermodynamically stable. This is a different result from that of the usual Schwarichild black hole. Further, by studying the influence of generalized uncertainty principle on non-commutative black hole thermodynamics, the quantum corrections from generalized uncertainty principle for temperature, entropy and heat capacity of the non-commutative Schwarzschild black hole are given. It is found that with considering this quantum gravity effect, the obtained black hole entropy contains the item of are alogarithm. If the effect of the generalized uncertainty principle is neglected, the corrected black hole entropy can return to that in the usual case of Beckenstein-Hawing area law. Similarly, the corrected black hole temperature and heat capacity can also return to their counterparts in the case of usual Schwarzschild black hole when this quantum gravity effect is ignored.

In this study, we delve into the observational implications of rotating Loop Quantum Black Holes (LQBHs) within an astrophysical framework. We employ semi-analytical General Relativistic Radiative Transfer (GRRT) computations to study the emission from the accretion flow around LQBHs. Our findings indicate that the increase of Loop Quantum Gravity (LQG) effects results in an enlargement of the rings from LQBHs, thereby causing a more circular polarization pattern in the shadow images. We make comparisons with the Event Horizon Telescope (EHT) observations of Sgr A* and M87*, which enable us to determine an upper limit for the polymetric function P in LQG. The upper limit for Sgr A* is 0.2, while for M87* it is 0.07. Both black holes exhibit a preference for a relatively high spin (a ≳ 0.5 for Sgr A* and 0.5 ≲ a ≲ 0.7 for M87*). The constraints for Sgr A* are based on black hole spin and ring diameter, whereas for M87*, the constraints are further tightened by the polarimetric pattern. In essence, our simulations provide observational constraints on the effect of LQG in supermassive black holes (SMBH), providing the most consistent comparison with observation.

Black Holes of primordial origin (PBHs) can constitute a large fraction of dark matter (DM) in the Universe. If light enough, they can emit a sizeable amount of Hawking radiation, which may be detected by dark matter experiments and be used to set constraints on the fraction of PBHs as DM components. Lately, these constraints have been extended to spinning PBHs, and it is very important to extend such analyses to other black hole metrics, in particular in the perspective of a signal detection. Recent works on black holes modification by quantum gravity effects have resulted in metrics that are regular at the black hole center, solving the singularity problem. We will present a generalization of the existing formalism to the generic class of spherically symmetric and static black holes, determining the short-range potentials for the equations of motion for these metrics. Using the public code BlackHawk, we will show how the Hawking radiation is modified for such black holes, and we will in particular focus on the case of polymerized black holes, which are black hole solutions arising from loop quantum gravity.

In this paper, we construct an effective rotating loop quantum black hole (LQBH) solution, starting from the spherical symmetric LQBH by applying the Newman-Janis algorithm modified by Azreg-A\"{i}nou's non-complexification procedure, and study the effects of loop quantum gravity { (LQG) on its shadow}. Given the rotating {LQBH}, we discuss its horizon, ergosurface, and regularity {as} $r \to 0$. Depending on the values of the specific angular momentum $a$ and the polymeric function $P$ arising from {LQG}, we {find} that the rotating solution we obtained can represent a regular black hole, a regular extreme black hole, or a regular spacetime {without horizon (a non-black-hole solution)}. We also {study} the effects of {LQG} and rotation, and {show} that, in addition to the specific angular momentum, the polymeric function {also} causes deformations in the size and shape of the black hole shadow. Interestingly, for a given value of $a$ and inclination angle $\theta_0$, the apparent size of the shadow monotonically decreases, and the shadow gets more distorted with increasing $P$. We also {consider the effects of $P$ on the deviations from the circularity of the shadow, and find} that the deviation from circularity increases with increasing $P$ for fixed values of $a$ and $\theta_0$. Additionally, we explore the observational implications of $P$ in comparison with the latest Event Horizon Telescope (EHT) observation of the supermassive black hole, M$87$. The connection between the shadow radius and quasinormal modes in the eikonal limit as well as {the} deflection of massive particles are also considered.

In this review, we discuss the effects of quantum gravity on black hole physics. After a brief review of the origin of the minimal observable length from various quantum gravity theories, we present the tunneling method. To incorporate quantum gravity effects, we modify the Klein–Gordon equation and Dirac equation by the modified fundamental commutation relations. Then we use the modified equations to discuss the tunneling radiation of scalar particles and fermions. The corrected Hawking temperatures are related to the quantum numbers of the emitted particles. Quantum gravity corrections slow down the increase of the temperatures. The remnants are observed as [Formula: see text]. The mass is quantized by the modified Wheeler–DeWitt equation and is proportional to n in quantum gravity regime. The thermodynamical property of the black hole is studied by the influence of quantum gravity effects.

In a recent article (Deglmann et al. in Ann Phys (NY) 475:169948, 2025), the authors obtained a static, cylindrically symmetric Anti-de Sitter (AdS) black string (BS) solutions, which are cylindrical generalizations of black holes (BHs), surrounded by a cloud of strings (CS) and the quintessence field (QF), and discussed its properties. In the present study, we present a comprehensive analysis of cylindrically symmetric AdS BSs surrounded by CS and QF. Our analysis yields several significant results. We demonstrate that the presence of CS (parameter α) and QF (parameters c and w) reduces the radius of circular photon orbits (CPO) and BH shadow size, with measurements constrained by Event Horizon Telescope (EHT) observations of Sagittarius A*. We find that time-like particle orbits show increased energy with higher α and c values. We calculate that C-energy, representing gravitational energy within cylindrical radius, decreases with radial distance but exhibits distinct responses to CS and QF parameters. We observe that scalar perturbation potential increases r for specific α and c values, indicating stronger field-spacetime interactions away from the BS. We determine that Hawking temperature increases linearly with Schwarzschild radius, with parameter-dependent behavior varying based on QF state parameter w. These results demonstrate how CS and QF significantly modify the geodesic, perturbative, and thermodynamic properties of AdS BS, with potential observational implications for gravitational lensing, accretion disk dynamics, and BH evaporation signatures in future astronomical observations.

This paper provides an extension for Hawking temperature of Reissner–Nordström-de Sitter (RN-DS) black hole (BH) with global monopole as well as [Formula: see text]D charged black hole. We consider the black holes metric and investigate the effects of quantum gravity ([Formula: see text]) on Hawking radiation. We investigate the charged boson particles tunneling through the horizon of black holes by using the Hamilton–Jacobi ansatz phenomenon. In our investigation, we study the quantum radiation to analyze the Lagrangian wave equation with generalized uncertainty principle and calculate the modified Hawking temperatures for black holes. Furthermore, we analyze the charge and correction parameter effects on the modified Hawking temperature and examine the stable and unstable condition of RN-DS BH with global monopole as well as [Formula: see text]D charged black hole.