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Exploring physical properties of compact stars in f(R,T)-gravity:An embedding approach

Chinese Physics C 2020年第10期44卷 190-204页

作者： Ksh.Newton Singh Abdelghani Errehymy Farook Rahaman Mohammed Daoud Department of Physics National Defence AcademyKhadakwaslaPune-411023India Department of Mathematics Jadavpur UniversityKolkata-700032India Laboratory of High Energy Physics and Condensed Matter(LPHEMaC) Department of PhysicsFaculty of Sciences Aïn ChockUniversity of Hassan IIB.P.5366 MaarifCasablanca 20100Morocco Department of Physics Faculty of SciencesUniversity of Ibn TofailB.P.133Kenitra 14000Morocco Abdus Salam International Centre for Theoretical Physics MiramareTrieste 34151Italy

Solving field equations exactly in f(R,T)−gravity is a challenging *** do so,many authors have adopted different methods such as assuming both the metric functions and an equation of state(EoS)and a metric ***,such methods may not always lead to well-behaved solutions,and the solutions may even be rejected after complete ***,very recent studies on embedding class-one methods suggest that the chances of arriving at a well-behaved solution are very high,which is *** the class-one approach,one of the metric potentials is estimated and the other can be obtained using the Karmarkar *** this study,a new class-one solution is proposed that is well-behaved from all physical points of *** nature of the solution is analyzed by tuning the f(R,T)−coupling parameterχ,and it is found that the solution leads to a stiffer EoS forχ=−1 than that forχ=*** is because for small values ofχ,the velocity of sound is higher,leading to higher values of Mmax in the M−R curve and the EoS parameterω.The solution satisfies the causality condition and energy conditions and remains stable and static under radial perturbations(static stability criterion)and in equilibrium(modified TOV equation).The resulting M−R diagram is well-fitted with observed values from a few compact stars such as PSR J1614-2230,Vela X-1,Cen X-3,and SAX ***,for different values ofχ,the corresponding radii and their respective moments of inertia have been predicted from the M−I curve.

关键词： f(R,T)-gravity Karmarkar's condition exact solutions compact star

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compact stars in F(R)Gravity Theory

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原子核物理评论 2024年第3期41卷 890-899页

作者： KATSURAGAWA Taishi NUMAJIRI Kota CUI Yongxiang NOJIRI Shin’ichi Institute of Astrophysics Central China Normal UniversityWuhan 430079China Department of Physics Nagoya UniversityNagoya 464-8602Japan Kobayashi-Maskawa Institute for the Origin of Particles and the Universe Nagoya UniversityNagoya 464-8602Japan

F(R)gravity is a modified gravity theory,and its applications for the compact star have attracted attention in the last *** review the basics of the F(R)gravity theory and the modified Tolman-Oppenheimer-Volkoff(TOV)*** studies show that the model dependence of equation of state(EOS)and modification of gravity degenerate to each other,which suggests the mass-radius(M-R)relation of the compact star alone cannot completely determine the EOS of the inner ***,the effects of a new scalar field predicted in F(R)gravity on both the internal and external structure of the compact star are illustrated in the benchmark R^(2)***,We discuss the future directions for testing gravitational theories by observational measurements of the compact stars.

关键词： modified gravity compact star TOV equation

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Strange quark star and the parameter space of the quasi-particle model

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Communications in Theoretical Physics 2021年第10期73卷 125-131页

作者： Wen-Hua Cai Qing-Wu Wang College of physics Sichuan UniversityChengdu 610064China

The properties of strange quark stars are studied within the quasi-particle model. Taking into account chemical equilibrium and charge neutrality, the equation of state(EOS) of(2+ 1)-flavor quark matter is obtained. We illustrate the parameter spaces with constraints from two aspects: one is based on the astronomical results of PSR J0740+ 6620 and GW 170 817,and the other is based on the constraints proposed from the theoretical study of a compact star that the EOS must ensure the tidal deformability Λ_(1.4)=190_(-120)^(+390) and support a maximum mass above 1.97M⊙. It is found that neither type of constraints can restrict the parameter space of the quasi-particle model in a reliable region and thus we conclude that the low mass compact star cannot be a strange quark star.

关键词： strange quark compact star tidal deformability quasi-particle model neutron star

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Neutron star cooling and GW170817 constraint within quark-meson coupling models

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Chinese Physics C 2021年第2期45卷 531-547页

作者： Odilon Lourenço César H.Lenzi Mariana Dutra Tobias Frederico M.Bhuyan Rodrigo Negreiros César V.Flores Guilherme Grams Débora P.Menezes Departamento de Física Instituto Tecnológico de AeronáuticaDCTA12228-900São Josédos CamposSPBrazil Department of Physics Faculty of ScienceUniversity of MalayaKuala Lumpur 50603Malaysia Atomic Molecular and Optical Research Group Advanced Institute of Materials ScienceTon Duc Thang UniversityHo Chi Minh CityVietnam Faculty of Applied Sciences Ton Duc Thang UniversityHo Chi Minh CityVietnam Instituto de Física Universidade Federal Fluminense 20420NiteróiRJBrazil Centro de Ciências Exatas Naturais e TecnológicasUEMASULRua Godofredo Viana 1300Centro CEP:65901-480ImperatrizMaranhãoBrazil Departamento de Física Universidade Federal de Santa CatarinaFlorianópolisSCCP 476CEP 88.040-900Brazil Univ.Lyon Univ.Claude Bernard Lyon 1CNRS/IN2P3IP2I LyonUMR 5822F-69622VilleurbanneFrance

In the present work,we used five different versions of the quark-meson coupling(QMC)model to compute astrophysical quantities related to the GW170817 event and the neutron star cooling *** of the models are based on the original bag potential structure and three versions consider a harmonic oscillator potential to confine *** bag-like models also incorporate the pasta phase used to describe the inner crust of neutron *** a simple method studied in the present work,we show that the pasta phase does not play a significant ***,the QMC model that satisfies the GW170817 constraints with the lowest slope of the symmetry energy exhibits a cooling profile compatible with observational data.

关键词： equation of state compact star cooling in stars quark-meson coupling models tidal deformability neutron star merger

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Static fluid spheres admitting Karmarkar condition

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Chinese Physics C 2020年第3期44卷 137-147页

作者： Ksh.Newton Singh Ravindra K.Bisht S.K.Maurya Neeraj Pant Department of Physics National Defence AcademyKhadakwaslaPune-411023India Department of Mathematics Jadavpur UniversityKolkata-700032India Department of Mathematics National Defence AcademyKhadakwaslaPune-411023India Department of Mathematical and Physical Sciences College of Arts and ScienceUniversity of NizwaNizwaSultanate of Oman

We explore a new relativistic anisotropic solution of the Einstein field equations for compact stars based on embedding class one *** this purpose,we use the embedding class one methodology by employing the Karmarkar *** this methodology,we obtain a particular differential equation that connects both the gravitational potentials e^λ and e^ν.We solve this particular differential equation choosing a simple form of generalized gravitational potential grr to describe a complete structure of the space-time within the stellar *** determining this space-time geometry for the stellar models,we discuss thermodynamical observables including radial and tangential pressures,matter density,red-shift,velocity of sound,etc.,in the stellar *** also perform a complete graphical analysis,which shows that our models satisfy all the physical and mathematical requirements of ultra-high dense collapsed ***,we discuss the moment of inertia and M-R curve for rotating and non-rotating stars.

关键词： Karmarkar's condition exact solutions compact star general relativity

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Anisotropic strange quark star in Finch-Skea geometry and its maximum mass for non-zero strange quark mass(m_(s)≠0)

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Chinese Physics C 2023年第5期47卷 195-210页

作者： B.Das K.B.Goswami A.Saha P.K.Chattopadhyay Department of Physics Coochbehar Panchanan Barma UniversityVivekananda StreetCoochbehar 736101West BengalIndia Department of Physics Alipurduar CollegeAlipurduar 736122West BengalIndia

A class of relativistic astrophysical compact objects is analyzed in the modified Finch-Skea geometry described by the MIT bag model equation of state of interior matter,p=1/3(ρ-4B),where B is known as the bag constant.B plays an important role in determining the physical features and structure of strange *** consider the finite mass of the strange quark(m_(s)≠0) and study its effects on the stability of quark matter inside a *** note that the inclusion of strange quark mass affects the gross properties of the stellar configuration,such as maximum mass,surface red-shift,and the radius of strange quark *** apply our model physically,we consider three compact objects,namely,(ⅰ) VELA X-1,(ⅱ) 4U 1820-30,and(ⅲ) PSR J 1903+327,which are thought to be strange *** range of B is restricted from 57.55 to Bstable(MeV/fm3),for which strange matter might be stable relative to iron(^(56)Fe).However,we also observe that metastable and unstable strange matter depend on B and *** energy conditions hold well in this *** in terms of the Lagrangian perturbation of radial pressure is studied in this paper.

关键词： compact star strange star anisotropy MIT EoS strange quark mass

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A new class of viable and exact solutions of EFEs with Karmarkar conditions:an application to cold star modeling

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Research in Astronomy and Astrophysics 2021年第5期21卷 71-83页

作者： Neeraj Pant Megandhren Govender Satyanarayana Gedela Department of Mathematics National Defence AcademyKhadakwaslaPune-411023India Department of Mathematics Faculty of Applied SciencesDurban University of TechnologyDurbanSouth Africa Department of Mathematics SSJ CampusKumaun UniversityAlmora-263601India

In this work we present a theoretical framework within Einstein’s classical general relativity which models stellar compact objects such as PSR J1614-2230 and SAX *** Einstein field equations are solved by assuming that the interior of the compact object is described by a class I *** so-called Karmarkar condition arising from this requirement is integrated to reduce the gravitational behaviour to a single generating *** appealing to physics we adopt a form for the gravitational potential which is sufficiently robust to accurately describe compact *** model satisfies all the requirements for physically realistic stellar structures.

关键词： compact star anisotropy embedding class Einstein field equations adiabatic index

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Class of Charged Fluid Balls in General Relativity

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International Journal of Astronomy and Astrophysics 2016年第4期6卷 494-511页

作者： A. Sah Prakash Chandra Department of Mathematics M B Govt. P G College Haldwani India

In the present study, we have obtained a new analytical solution of combined Einstein-Maxwell field equations describing the interior field of a ball having static spherically symmetric isotropic charged fluid within it. The charge and electric field intensity are zero at the center and monotonically increasing towards the boundary of the fluid ball. Besides these, adiabatic index is also increasing towards the boundary and becomes infinite on it. All other physical quantities such as pressure, density, adiabatic speed of sound, charge density, adiabatic index are monotonically decreasing towards the surface. Causality condition is obeyed at the center of ball. In the limiting case of vanishingly small charge, the solution degenerates into Schwarzchild uniform density solution for electrically neutral fluid. The solution joins smoothly to the Reissner-Nordstrom solution over the boundary. We have constructed a neutron star model by assuming the surface density . The mass of the neutron star comes with radius 14.574 km.

关键词： Exact Solution Einstein’s Field Equations Charged Fluid Ball compact star General Relativity

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Spherical Anisotropic Fluid Distribution in General Relativity

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World Journal of Mechanics 2016年第12期6卷 487-504页

作者： A. Sah Prakash Chandra Department of Mathematics M B Govt. P G College Haldwani India

In the present investigation of a spherically symmetric electrically neutral anisotropic static fluid, we present a new solution of the Einstein’s general relativistic field equations. The solution shows positive finite central pressures, central density and central red shift. The causality condition is obeyed at the centre. The anisotropy parameter is zero at the center and monotonically increasing toward the surface. The adiabatic index is also increasing towards the surface. All the other physical quantities such as matter-energy density, radial pressure, tangential pressure, velocity of sound and red shift are monotonically decreasing towards the surface. Further by assuming the surface density , we have constructed a model of massive neutron star with mass 2.95 with radius 18 km with all degree of suitability.

关键词： Anisotropic Fluid Ball Exact Solutions Einsteins Field Equations compact star General Relativity

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