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G. Mustafa

Publications and source records attributed to G. Mustafa.

At least 91 records · Page 5Linked to original sources
arXiv2024

Thermal analysis and Joule-Thomson expansion of black hole exhibiting metric-affine gravity

This study examines a recently hypothesized black hole, which is a perfect solution of metric-affine gravity with a positive cosmological constant, and its thermodynamic features as well as the Joule-Thomson expansion. We develop some thermodynamical quantities, such as volume, Gibbs free energy, and heat capacity, using the entropy and Hawking temperature. We also examine the first law of thermodynamics and thermal fluctuations, which might eliminate certain black hole instabilities. In this regard, a phase transition from unstable to stable is conceivable when the first law order corrections are present. Besides that, we study the efficiency of this system as a heat engine and the effect of metric-affine gravity for physical parameters $q_e$, $q_m$, $κ_{\mathrm{s}}$, $κ_{\mathrm{d}}$ and $κ_{\mathrm{sh}}$. Further, we study the Joule-Thomson coefficient, and the inversion temperature and also observed the isenthalpic curves in the $T_i -P_i$ plane. In metric-affine gravity, a comparison is made between the Van der Waals fluid and the black hole to study their similarities and differences.

gr-qc↗
arXiv2023

A study on matter accretion onto charged black hole solution in metric-affine gravity

This study deals with astrophysical accretion onto the charged black hole solution, which is sourced by the dilation, spin, and shear charge of matter in metric affine gravity. The metric affine gravity defines the link between torsion and nonmetricity in space-time geometry. In the current analysis, we study the accretion process of various perfect fluids that are accreting near the charged black hole in the framework of metric affine gravity. Within the domain of accretion, multiple fluids have been examined depending on the value of $f_1$. The ultra-stiff, ultra-relativistic, and sub-relativistic fluids are considered to discuss the accretion. In the framework of equations of state, we consider isothermal fluids for this investigation. Further, we explore the effect of polytropic test fluid in relation to accretion discs, and it is presented in phase diagrams. Some important aspects of the accretion process are investigated. Analyzing the accretion rate close to a charged black hole solution, typical behavior is created and discussed graphically.

gr-qc↗
arXiv2023

Study on physical properties and maximum mass limit of Finch-Skea anisotropic model under Karmarkar condition in $f(Q)$-gravity

The primary objective of this work is to study the dynamical characteristics of an anisotropic compact star model with spherical symmetry. This investigation is conducted in the framework of $f(Q)$ modified gravity. To simplify the calculations, we employ the Karmarkar condition and derive a differential equation that establishes a relationship between two crucial components of the spacetime namely $e^ν$ and $e^λ$. Additionally, we incorporate the well-known Finch-Skea structure as the component representing $g_{rr}$ and subsequently find the resulting form of the component $g_{tt}$ from the relation of metric functions to formulate the precise solutions for the stellar structure. To assess the behavior of the anisotropic fluid and stability of the compact star, we use the observed values of mass and radius for the compact star model $PSR J0437-4715$. The graphical analysis depicts that the stellar structure possesses physical viability and exhibits intriguing properties. Furthermore, we predicted the mass-radius relation along with the maximum mass limit of several objects for different parameter values by assuming two different surface densities. It is discovered that the compactness rises when density increases.

gr-qc↗
arXiv2023

Joule-Thomson expansion and tidal force effects of AdS black holes surrounded by Chaplygin dark fluid

This study examines a recently hypothesized black hole. We study the Joule-Thomson coefficient, the inversion temperature and also the isenthalpic curves in the $T_i -P_i$ plane. A comparison is made between the Van der Waals fluid and the black hole to study their similarities and differences. The Joule-Thomson coefficient, the inversion curves and the isenthalpic curves are discussed inAdS black holes surrounded by Chaplygin dark fluid. In $T -P$ plane, the inversion temperature curves and isenthalpic curves are obtained with different parameters. Next, we explore the radial timelike geodesics that leads us to explore the tidal force effects for a radially in-falling particle in such black hole spacetime. We also numerically solve the geodesic deviation equation for two nearby radial geodesics for a freely falling particle. Our analysis shows that contrary to the Schwarzschild spacetime, the tidal forces don't become zero at spatial infinity due to the lack of asymptotic flatness because of the presence of a non-zero cosmological constant. The geodesic separation profile shows an oscillating trend and depends on the dynamic spacetime parameters $q, B$ and $Λ$.

gr-qc↗
arXiv2023

Ricci inverse gravity wormholes

The current study deals with the new wormhole solutions in the background of fourth order new modified Ricci inverse gravity. Two new classes of the wormhole solutions are analyzed by showing the valid region for the main part of wormhole geometry under the affect of involved parameters. The embedded diagrams for both generic shape functions are also presented, which are connecting upper and lower Universes. In order to check the existence of these wormhole solutions, energy conditions are included in the current analysis. In the maximum regions, all energy conditions are violated, which confirms the presence of exotic matter in the background of Ricci inverse gravity. Stability analysis for both wormhole solutions is explored within the scope of speed of sounds parameters. Conclusively, some highlights from this research confirm the realistic nature and viability of these wormhole solutions in Ricci inverse gravity.

gr-qc↗
arXiv2023

Cosmic evolution in $f(Q,T)$ gravity: Exploring a higher-order time-dependent function of deceleration parameter with observational constraints

In this research paper, we explore a well-motivated parametrization of the time-dependent deceleration parameter, characterized by a cubic form, within the context of late time cosmic acceleration. The current analysis is based on the $f(Q,T)$ gravity theory, by considering the background metric as the homogeneous and isotropic Friedmann Lemaître Robertson Walker (FLRW) metric. Investigating the model reveals intriguing features of the late universe. To constrain the model, we use the recent observational datasets, including cosmic chronometer (CC), Supernovae (SNIa), Baryon Acoustic Oscillation (BAO), Cosmic Microwave Background Radiation (CMB), Gamma Ray Burst (GRB), and Quasar (Q) datasets. The joint analysis of these datasets results in tighter constraints for the model parameters, enabling us to discuss both the physical and geometrical aspects of the model. Moreover, we determine the present values of the deceleration parameter ($q_0$), the Hubble parameter ($H_0$), and the transition redshift ($z_t$) from deceleration to acceleration ensuring consistency with some recent results of Planck 2018. Our statistical analysis yields highly improved results, surpassing those obtained in previous investigations. Overall, this study presents valuable insights into the higher order $q(t)$ model and its implications for late-time cosmic acceleration, shedding light on the nature of the late universe.

gr-qc↗
arXiv2023

Circular orbits and accretion disk around AdS black holes surrounded by dark fluid with Chaplygin-like equation of state

In the present work we study the geodesic motion and accretion process of a test particle near an Anti-de Sitter (ADS) BH surrounded by a dark fluid with a Chaplygin-like equation. Within the defined paradigm, we investigate on the equatorial plane and examine circular geodesics along with their features related to stabilities, radiation energy flux, oscillations and orbits. The general form of the fluid accretion onto the AdS BH through dynamical analysis and mass expansion also has discussed in a depth. Additionally, a few more interesting topics, e.g. the effective potential, angular momentum, specific energy, radiation energy and epicyclic frequencies have also been examined thoroughly. All the attributes are physically acceptable within the observational signatures and ranges.

gr-qc↗
arXiv2023

Strong Gravitational Lensing by Sgr A* and M87* Black Holes embedded in Dark Matter Halo exhibiting string cloud and quintessential field

We investigate the strong gravitational lensing phenomena caused by a black hole with a dark matter halo. In this study, we examine strong gravitational lensing with two significant dark matter models: the universal rotation curve model and the cold dark matter model. To do this, we first numerically estimate the strong lensing coefficients and strong deflection angles for both the universal rotation curve and cold dark matter models. It is observed that the deflection angle, denoted as $α_D$, increases with the parameter $α$ while holding the value of $γ\cdot 2M$ constant. Additionally, it increases with the parameter $γ\cdot 2M$ while keeping the value of $α$ constant. The strong deflection angle, $α_D$, for the black hole with a dark matter halo, with parameters $α=0$ and $γ\cdot 2M$, greatly enhances the gravitational bending effect and surpasses the corresponding case of the standard Schwarzschild black hole ($A=0, B=0, α=0, γ\cdot 2M=0$). Furthermore, we investigate the astrophysical consequences through strong gravitational lensing observations, using examples of various supermassive black holes such as $M87^{*}$ and $SgrA^{*}$ located at the centers of several galaxies. It is observed that black holes with dark matter halos can be quantitatively distinguished and characterized from the standard Schwarzschild black hole ($A=0, B=0, α=0, γ\cdot 2M=0$). The findings in our analysis suggest that observational tests for black holes influenced by dark matter halos are indeed feasible and viable.

gr-qc↗
arXiv2023

Exploring Tidal Force Effects and Shadow Constraints for Schwarzschild-like Black Hole in Starobinsky-Bel-Robinson Gravity

The current manuscript deals with the tidal force effects, geodesic deviation, and shadow constraints of the Schwarzschild-like black hole theorised in Starobinsky-Bel-Robinson gravity exhibiting M-theory compactification. In the current analysis, we explore the radial and angular tidal force effects on a radially in-falling particle by the central black hole, which is located in this spacetime. We also numerically solve the geodesic deviation equation and study the variation of the geodesic separation vector with the radial coordinate for two nearby geodesics using suitable initial conditions. All the obtained results are tested for Sag A* and M87* by constraining the value of the stringy gravity parameter $β$ using the shadow data from the event horizon telescope observations. All the results are compared with Schwarzschild black hole spacetime. In our study, we found that both the radial and angular tidal forces experienced by a particle switch their initial behaviour and turn compressive and stretching, respectively, before reaching the event horizon. The geodesic deviation shows an oscillating trend as well for the chosen initial condition. For the constrained value of $β$, we see that the spacetime geometry generated by Sag A* and M87* is effectively same for both Schwarzschild and Starobinsky-Bel-Robinson black hole. Furthermore, we also calculated the angular diameter of the shadow in Starobinsky-Bel-Robinson black hole and compared with the Schwarzschild black hole. It is observed that the angular diameter of shadow for M87* and Sgr A* in Starobinsky-Bel-Robinson black hole is smaller than the Schwarzschild black hole. The calculated results satisfy the event horizon telescope observational constraints. Finally, we have concluding remarks.

gr-qc↗
arXiv2023

Exploring Late-Time Cosmic Acceleration with EoS Parameterizations in Horava-Lifshitz Gravity via Baryon Acoustic Oscillations

In our study, we have adopted the framework of Horava-Lifshitz gravity to model the Universe's dark matter and dark energy components. Specifically, we have considered two recent parametrizations for dark energy models: the CBDRM-type and CADMM-type parameterizations. In our analysis, we have explicitly expressed the Hubble parameter, denoted as $H(z)$, for these two distinct dark energy models. By doing so, we have aimed to investigate and quantify the accelerated cosmic expansion rate characterizing the late-time Universe. Our study uses a wide range of datasets. This dataset consists of recent measurements of baryon acoustic oscillations (BAO) collected over a period of twenty years with the Cosmic Chronometers (CC) dataset, Type Ia supernovae (SNIa) dataset, the Hubble diagram of gamma-ray bursts (GRBs), quasars (Q), and the latest measurement of the Hubble constant (R22). Consequently, we present a crucial aspect of our study by plotting the $r_{d}$ vs. $H_{0}$ plane. In the context of the $Λ$CDM model, after incorporating all the datasets, including the R22 prior, we obtain the following results: $H_{0}$ = $71.674089 \pm 0.734089$ $km s^{-1} Mpc^{-1}$ and $r_d = 143.050380 Mpc \pm 3.702038$. For the CBDRM model, we find $H_{0}$ = $72.355058 \pm 1.004604$ $km s^{-1} Mpc^{-1}$ and $r_d = 144.835069 Mpc \pm 2.378848$. In the case of the CADMM model, our analysis yields $H_{0}$ = $72.347804 \pm 0.923328$ $km s^{-1} Mpc^{-1}$ and $r_d = 144.466836 Mpc \pm 4.288758$. We have conducted cosmographic analyses for both of the proposed parameterizations in comparison to the $Λ$CDM paradigm. Additionally, we have applied Diagnostic tests to investigate the evolution of both models. Finally, the Information Criteria test demonstrates that the $Λ$CDM model emerges as the preferred choice among the models we have considered.

astro-ph.CO↗
arXiv2023

Accretion disk around Reissner-Nordström black hole coupled with a nonlinear electrodynamics field

The phenomenon by which matter accumulates in the vicinity of a huge celestial object is known as accretion. The gravitational energy is excreted as a consequence of infalling matter onto compact objects. The accretion procedure around celestial bodies like neutron stars, white dwarfs, and black holes has considerable importance because of its ability to transform gravitational energy into radiation. This study investigates the particle's geodesic motion and accretion around the spherically symmetric Reissner-Nordström black hole coupled with a nonlinear electrodynamics field utilizing isothermal fluid. The formation of the disc-like structure in the accretion process arises from the geodesic motion exhibited by particles near the black hole. The circular orbits, radiant flux energy, radioactive efficiency, and radiant temperature, can be determined. Our study focuses on the examination of particles exhibiting stable circular orbits within the equatorial plane. We analyze the perturbations experienced by particles throughout employing restoring forces and the oscillatory behavior of the particles around a compact object. We conduct an analysis of the fluid's critical flow and maximum accretion rate. Our results show how the black hole parameter $ζ$ and charge $q$ affect the circular geodesic of particles and the maximum accretion rate of the Reissner-Nordström black hole coupled with nonlinear electrodynamics.

gr-qc↗
arXiv2023

Constraints on the Parameterized Deceleration Parameter in FLRW Universe

Confirmation of accelerated expansion of the universe probed the concept of dark energy theory, and since then, numerous models have been introduced to explain its origin and nature. The present work is based on reconstructing dark energy by parametrization of the deceleration parameter in the FRW universe filled with radiation, dark matter, and dark energy. We have chosen some well-motivated parametrized models 1-3 in an attempt to investigate the energy density in terms of deceleration parameters by estimating the cosmological parameters with the help of different observational datasets. Also, we have introduced a new model 4 for the parametrization of the deceleration parameter. Then we analyzed the cosmography parameters using the best-fit values of the parameters. Using the information criteria, we have examined the viability of the models.

gr-qc↗
arXiv2023

Matter accretion onto the magnetically charged Euler-Heisenberg black hole with scalar hair

This paper deals with astrophysical accretion onto the magnetically charged Euler-Heisenberg black holes with scalar hair. We examine the accretion process of a variety of perfect fluids, including polytropic and isothermal fluids of the ultra-stiff, ultra-relativistic, and sub-relativistic forms, when fluid is accreting in the vicinity of the black hole. By using the Hamiltonian dynamical approach, we can find the sonic or critical points numerically for the various types of fluids that are accreting onto the black hole. Furthermore, for several types of fluids, the solution is provided in closed form, expressing phase diagram curves. We compute the mass accretion rate of a magnetically charged Euler-Heisenberg black hole with scalar hair. We observe that the maximum accretion rate is attained for small values of the black hole parameters. We may be able to understand the physical mechanism of accretion onto black holes using the outcomes of this investigation.

gr-qc↗
arXiv2023

Data Analysis of three parameter models of deceleration parameter in FRW Universe

Constraining the dark energy deceleration parameter is one of the fascinating topics in the recent cosmological paradigm. This work aims to reconstruct the dark energy using parametrization of the deceleration parameter in a flat FRW universe filled with radiation, dark energy, and pressure-less dark matter. Thus, we have considered four well-motivated parameterizations of q(z), which can provide the evolution scenario from the deceleration to acceleration phase of the Universe. We have evaluated the expression of the corresponding Hubble parameter of each parametrization by imposing it into the Friedmann equation. We have constrained the model parameter through H(z), Pantheon, and baryons acoustic oscillation (BOA) data. Next, we have estimated the best-fit values of the model parameters by using Monte Carlo Markov Chain (MCMC) technique and implementing H(z)+ BAO+SNe-Ia dataset. Then we analyzed the cosmographic parameter, such as deceleration, jerk, and snap parameters, graphically by employing the best-fit values of the model parameter. Moreover, we have analyzed statefinder and Om diagnostics parameters for each scenario to discriminate various dark energy models. Using the information criteria, the viability of the models have examined. In the end, we have analogized our outcomes with the standard ΛCDM model to examine the viability of our models

gr-qc↗
arXiv2023

The effect of gravitational decoupling on constraining the mass and radius for the secondary component of GW190814 and other self-bound strange stars in f(Q)-gravity theory

Inspired by the conundrum of the gravitational event, GW190814 which brings to light the coalescence of a 23 $ M_{\odot}$ black hole with a yet to be determined secondary component, we look to modelling compact objects within the framework of $f(\mathcal{Q})$ gravity by employing the method of gravitational decoupling. We impose a quadratic equation of state (EOS) for the interior matter distribution which in the appropriate limit reduces to the MIT bag model. The governing field equations arising from gravitational decoupling bifurcates into the $ρ=θ^0_0$ and $p_r=θ^1_1$ sectors leading to two distinct classes of solutions. Both families of solutions are subjected to rigorous tests qualifying them to describe a plethora of compact objects including neutron stars, strange stars and the possible progenitor of the secondary component of GW190814. Using observational data of mass-radius relations for compact objects LMC X-4, Cen X-3, PSR J1614-2230 and PSR J0740+6620 we show that it is possible to generate stellar masses and radii beyond 2.0 $ M_{\odot}$ for neutron stars. Our findings reveal that the most { suitable and versatile model in this framework is the quadratic EOS}, which accounts for a range of low mass stars as well as typical stellar candidates describing the secondary component of GW190814.

gr-qc↗
arXiv2023

Observational constraints on a logarithmic scalar field dark energy model and black hole mass evolution in the Universe

We propose a logarithmic parametrization form of energy density for the scalar field dark energy in the framework of the standard theory of gravity, which supports the necessary transition from the decelerated to the accelerated behavior of the Universe. The model under consideration is constrained by available observational data, including cosmic chronometers data-sets (CC), Baryonic Acoustic Oscillation (BAO) data-sets, and Supernovae (SN) data-sets, consisting of only two parameters $α$ and $β$. The combined $CC$+$BAO$+$SN$ data-sets yields a transition redshift of $z_{tr}=0.79^{+0.02}_{-0.02}$, where the model exhibits signature-flipping and is consistent with recent observations. For the combined data-sets, the present value of the deceleration parameter is calculated to be $q_{0}=-0.43^{+0.06}_{-0.06}$. Furthermore, the analysis yields constraints on both the parameter density value for matter and the present value of the Hubble parameter, with values of $Ω_{m0}=0.25849^{+0.00026}_{-0.00025}$ and $H_{0}=67.79_{-0.59}^{+0.59}$ $km/s/Mpc$, respectively, consistent with the results obtained from Planck 2018. Finally, the study investigates how the mass of a black hole evolves over time in a Universe with both matter and dark energy. It reveals that the black hole mass increases initially but stops increasing as dark energy dominates.

gr-qc↗
arXiv2023

On possible wormhole solutions supported by non-commutative geometry within $f(R, L_m)$ gravity

Non-commutativity is a key feature of spacetime geometry. The current article explores the traversable wormhole solutions in the framework of $f(R,L_m)$ gravity within non-commutative geometry. By using the Gaussian and Lorentzian distributions, we construct tideless wormholes for the nonlinear $f(R,L_m)$ model $f(R,L_m)=\dfrac{R}{2}+L_m^α$. For both cases, we derive shape functions and discuss the required different properties with satisfying behavior. For the required wormhole properties, we develop some new constraints. The influence of the involved model parameter on energy conditions is analyzed graphically which provides a discussion about the nature of exotic matter. Further, we check the physical behavior regarding the stability of wormhole solutions through the TOV equation. An interesting feature regarding the stability of the obtained solutions via the speed of sound parameters within the scope of average pressure is discussed. Finally, we conclude our results.

gr-qc↗
arXiv2023

Constraining study of circular orbits and accretion disk around nonlinear electrodynamics black hole

The very latest observation of $M87$ supermassive black hole (BH) by the Event Horizon Telescope (EHT) provides the accretion onto BHs is an interesting study in the theory of gravity. We study the geodesics structure and accretion near a nonlinear electrodynamics BH in strong and weak field approximations. These approximations provide the disc-like structure under the geodesic motion and accretion around the BH. Near the equatorial plane, we provide some new reasons to make circular orbits and accretion of test particles around the BH. Then we investigate perturbations, the critical speed of the fluid and the mass accretion rate of particles around the central object. The physical validity of this study shows that the parameter $β$ and $Q$ play an important role in the circular orbits and the mass accretion rate in strong and weak field approximations.

gr-qc↗