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Singularities of noncompact charged objects

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Chinese Physics B 2013年第3期22卷 192-195页

作者： M.Sharif g.abbas Department of Mathematics University of the PunjabQuaid-e-Azam CampusLahore-54590Pakistan

We formulate a model for noncompact spherical charged objects in the framework of noncommutative field *** Einstein-Maxwell field equations are solved with charged anisotropic *** choose matter and charge densities as functions of the two parameters,instead of defining these quantities in terms of the gaussian distribution *** is found that the corresponding densities and the Ricci scalar are singular in origin,whereas the metric is nonsingular,indicating a spacelike *** numerical solution of the horizon equation implies that there are two or one or no horizon（s）,depending on the *** also evaluate the Hawking temperature and find that a black hole with two horizons is evaporated to an extremal black hole with one horizon.

关键词： noncommutative geometry electromagnetic field spacetime singularity

Thermodynamics of Phantom Energy Accreting onto a Black Hole in Einstein–Power–Maxwell gravity

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Chinese Physics Letters 2013年第10期30卷 34-37页

作者： g.abbas R.M.Ramzan Department of Mathematics COMSATS Institute of Information TechnologySahiwal-67000Pakistan Department of Mathematics The Islamia University BahawalpurPakistan

We investigate the phantom energy accretion onto a 3D black hole formulated in the Einstein–Power–Maxwell theory,and present the conditions for critical accretion of phantom energy onto the black ***,we discuss the thermodynamics of phantom energy accreting onto the black hole and find that the first law of thermodynamics is easily satisfied while the second law and the generalized second law of thermodynamics remain invalid and conditionally valid,*** results for the Banados–Teitelboim–Zanelli black hole can be recovered by taking Maxwellian contribution equal to zero.

关键词： Maxwell black law Power

Physical aspects of anisotropic compact stars in f(T,T) gravity with off diagonal tetrad

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Chinese Physics C 2021年第8期45卷 190-205页

作者： M.Zubair Allah Ditta g.abbas Rabia Saleem Department of Mathematics COMSATS University IslamabadLahore CampusLahorePakistan Department of Mathematics The Islamia University of BahawalpurBahawalpurPakistan

This study addresses the formation of anisotropic compact star models in the background of f(T,T)gravity(where T and T represent the torsion and trace of the energy momentum tensor,respectively).f(T,T)gravity is an extension of the f(T)theory,and it allows a general non-minimal coupling between T and *** this setup,we apply Krori and Barua's solution to the static spacetime with the components ξ=Br^(2)+c and ψ=Ar^(2).To develop viable solutions,we select a well-known model f(T,T)=αT^(m)+βT+Ф(where α and β are coupling parameters,and Ф indicates the cosmological constant).We adopt the conventional matching of interior and exterior space time to evaluate the unknowns,which are employed in the stellar *** present a comprehensive discussion on the stellar properties to elaborate the anisotropic nature of compact stars corresponding to well-known models:PSRJ1416-2230,4U1608-52,CenX-3,EXO1785-248,and *** physical analysis,it is observed that the solution of compact spheres satisfy the acceptability criteria,and its models behave optimally and depict stability and consistency,in accordance with f(T,T)gravity.

关键词： f(T,T)gravity compact stars stellar models

Physical aspects of anisotropic compact stars in f(T,■) gravity with off diagonal tetrad

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Chinese Physics C 2021年第8期 195-210页

作者： M.Zubair Allah Ditta g.abbas Rabia Saleem Department of Mathematics COMSATS University Islamabad Department of Mathematics The Islamia University of Bahawalpur

This study addresses the formation of anisotropic compact star models in the background of f(T,■)gravity(where T and ■ represent the torsion and trace of the energy momentum tensor,respectively).f(T,■) gravity is an extension of the f(T) theory,and it allows a general non-minimal coupling between T and ■.In this setup,we apply Krori and Barua’s solution to the static spacetime with the components ξ=Br~2+c and Ψ=Ar~*** develop viable solutions,we select a well-known model f(T,■)=aT~m+β■+φ(where α and β are coupling parameters,and φ indicates the cosmological constant).We adopt the conventional matching of interior and exterior space time to evaluate the unknowns,which are employed in the stellar *** present a comprehensive discussion on the stellar properties to elaborate the anisotropic nature of compact stars corresponding to well-known models:PSRJ1416-2230,4U1608-52,CenX-3,EX01785-248,and *** physical analysis,it is observed that the solution of compact spheres satisfy the acceptability criteria,and its models behave optimally and depict stability and consistency,in accordance with f(T,■) gravity.

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Accretion around a hairy black hole in the framework of gravitational decoupling theory

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Chinese Physics C 2023年第12期47卷 180-194页

作者： H.Rehman g.abbas Department of Mathematics The Islamia University of BahawalpurBahawalpur Pakistan

We investigate astrophysical accretion onto a static and spherically symmetric hairy black hole withinthe framework of gravitational decoupling. To achieve this goal, we examine the accretion procedure for severaltypes of perfect fluids, including polytropic fluid and ultra-stiff, ultra-relativistic, radiation, and sub-relativistic isothermalfluids. Moreover, we determine the critical or sonic points for numerous fluid forms that are accreting ontothe black hole by utilizing the Hamiltonian dynamical approach. Additionally, the closed form of the solutions arepresented for a number of fluids, which are represented in phase diagram curves. We estimate the mass accretion rateof a static and spherically symmetric hairy black hole within the framework of gravitational decoupling. These findingsare helpful in constraining the parameters of black holes while physical matter accretes onto the black holes.

关键词： general relativity astrophysical accretion black hole

Thermodynamics under the impact of thermal fluctuations and quasi-normal modes of Euler-Heisenberg AdS BH in the framework of NLED

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Chinese Physics C 2023年第11期47卷 145-166页

作者： R.H.Ali g.abbas Department of Mathematics The Islamia University of BahawalpurBahawalpur Pakistan

We study the impact of thermal fluctuations on the thermodynamics,quasi-normal modes,and phase transitions of an anti-de Sitter Euler-Heisenberg black hole(BH)with a nonlinear electrodynamic *** anti-de Sitter Euler-Heisenberg BH with a nonlinear electrodynamic field is composed of four parameters:the mass,electric charge,cosmological constant,and Euler-Heisenberg *** calculate thermodynamic variables such as Hawking temperature,entropy,volume,and specific heat,which comply with the first law of ***,we use this BH to determine the thermodynamics and thermal fluctuations with the Euler-Heisenberg parameter to distinguish their effect on uncorrected and corrected thermodynamical *** derive the expression for corrected entropy to study the impact of thermal fluctuation with simple logarithmic corrections on unmodified thermodynamical potentials,including Helmholtz energy,pressure,gibbs free energy,and *** Euler-Heisenberg parameter improves BH stability at large ***,we analyze the local stability of the proposed BH,and the phase shifts of the BH are also investigated using temperature and specific *** there is a decrease in charge and an increase in r_(+)andα,the temperature shifts from an unstable region to a stable ***,increases in local stability are observed with each of these ***,we use null geodesics to deal with the effects of nonlinear electrodynamics on the quasi-normal modes of the Euler-Heisenberg anti-de Sitter *** null geodesics provide the angular velocity and Lyapunov exponent of the photon sphere,which are the same as the real and imaginary parts of the quasi-normal modes in the eikonal limit.

关键词： thermodynamics thermal fluctuation quasi normal modes and phase transition

Extended phase space thermodynamics of black hole with non-linear electrodynamic field

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Chinese Physics C 2023年第6期47卷 177-187页

作者： g.abbas R.H.Ali Department of Mathematics The Islamia University of BahawalpurBahawalpurPakistan

This paper deals with the thermodynamical properties of the black hole formulated in Einstein’s theory of relativity associated with a nonlinear electromagnetic *** transition of the black hole is analyzed using the mass,electric charge,coupling constant,and cosmological *** examine the thermodynamical aspects of exact black hole solutions to compute the black hole mass,temperature,entropy,gibbs free energy,specific heat,and critical exponents in the phase ***,we study the stability of the black hole solution using the specific heat and gibbs free *** examine the first and second phase changes and show a P-V criticality,which is similar to the van der Waals phase *** also examine the equation of the state and the critical exponents.

关键词： non-linear electrodynamic thermodynamics phase transition critical exponents

Strong gravitational lensing for photon coupled to Weyl tensor in Kiselev black hole

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Chinese Physics C 2020年第9期44卷 210-223页

作者： g.abbas Asif Mahmood M.Zubair Departmentof Mathematics The Islamia University of BahwalpurPakistan Department of Mathematics COMSATS UniversityIslamabadLahore CampusPakistan

The objective of the present work is to highlight the phenomena of strong gravitational lensing and deflection angle for the photon coupling with the Weyl tensor in a Kiselev black ***,we have extended the prior work of Chen and Jing(*** and ***,JCAP,10:002(2015))for a Schwarzschild black hole to a Kiselev black *** this purpose,the equation of motion for the photons coupled to the Weyl tensor,null geodesic,and equation of photon sphere in a Kiselev black hole spacetime have been *** is found that the equation of motion of the photons depends not only on the coupling between the photons and the Weyl tensor,but also on the polarization direction of the *** is a critical value of the coupling parameter,α,for the existence of the marginally circular photon orbit outside the event horizon,which depends on the parameters of the black hole and the polarization direction of the ***,the polarization directions of the coupled photons and the coupling parameter,α;both modify the features of the photon sphere,angle of deflection,and functions(^ˉa and^ˉb)owing to the strong gravitational lensing in the Kiselev black hole *** addition to this,the observable gravitational lensing quantities and the shadows of the Kiselev black hole spacetime are presented in detail.

关键词： relativity and gravitation gravitational lensing classical black holes deflection angle

Relativistic polytropic models of charged anisotropic compact objects

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Chinese Physics C 2023年第3期47卷 291-309页

作者： H.Nazar M.Azam g.abbas Riaz Ahmed R.Naeem Department of Mathematics The Islamia University of Bahawalpur BahawalpurPakistan Department of Mathematics Division of Science and TechnologyUniversity of EducationLahorePakistan Department of Mathematics Maharishi International UniversityFairfieldIAUSA

In this paper,we introduce new viable solutions to the Einstein-Maxwell field equations by incorporating the features of anisotropic matter distributions within the realm of the general theory of relativity(gR).To obtain these solutions,we employed the Finch-Skea spacetime,along with a generalized polytropic equation of state( EoS).We constructed various models of generalized polytropes by assuming different values of the polytropic index,i.e.,η=1/2,2/3,1,and ***,numerous physical characteristics of these considered models were studied via graphical analysis,and they were found to obey all the essential conditions for astrophysical compact ***,such outcomes of charged anisotropic compact star models could be reproduced in various other cases including linear,quadratic,and polytropic EoS.

关键词： general relativity exact solutions charged polytropic models anisotropy of pressure