In the present article,we introduce a completely new regular model for static,spherically symmetric celestial fluid spheres in embedding classⅠspacetime.In this regard,needfully,we propose a new suitable metric poten...In the present article,we introduce a completely new regular model for static,spherically symmetric celestial fluid spheres in embedding classⅠspacetime.In this regard,needfully,we propose a new suitable metric potential e^(λ(r))to generate the present model.The various analyses on energy density,pressure,anisotropic factor,mass,compactness parameter,redshift,and energy condition make sure the model is physically viable on the ground of model stars Vela X-1,Cen X-3,SMC X-4,and LMC X-4.The reported solutions also respect the equilibrium state by satisfying the Tolman-Oppenheimer-Volkoff(TOV)equation and ensure stability by satisfying the causality condition,condition on the adiabatic index,and Harrison-Zeldovich-Novikov condition.The generated M-R graph matches the ranges of masses and radii for the model compact stars.Additionally,this study provides estimates of the moment of inertia based on the I-M graph.展开更多
Based on the generalized uncertainty principle with maximum momentum arid minimal length, we discuss the equation of state of ideal ultra-relativistic Fermi gases at zero temperature. Maximum momentum avoids the probl...Based on the generalized uncertainty principle with maximum momentum arid minimal length, we discuss the equation of state of ideal ultra-relativistic Fermi gases at zero temperature. Maximum momentum avoids the problem that the Fermi degenerate pressure blows up since the increase of the Fermi energy is not limited. Applying this equation of state to the Tolman-Oppenheimer Volkoff （TOV） equation, the quantum gravitational effects on the cores of compact stars are discussed. In the center of compact stars, we obtain the singularity-free solution of the metric component, gtt ～-（1 ＋ 0.2185×r^2）. By numerically solving the TOV equation, we find that quantum gravity plays an important role in the region r～10^4α0（△x）min. Current observed masses of neutron stars indicate that the dimensionless parameter α0 cannot exceed 10^19.展开更多
The effects of gravitomagnetic force on plasma oscillations are investigated using the kinetic theory of homogeneous electrically neutral plasma in the absence of external electric or magnetic field. The random phase ...The effects of gravitomagnetic force on plasma oscillations are investigated using the kinetic theory of homogeneous electrically neutral plasma in the absence of external electric or magnetic field. The random phase assumption is employed neglecting the thermal motion of the electrons with respect to a fixed ion background. It is found that the gravitomagnetic force reduces the characteristic frequency of the plasma thus enhancing the refractive index of the medium. The estimates for the predicted effects are given for a typical white dwarf, pulsar, and neutron star.展开更多
The aim of this paper is to investigate modified f(R, ?) theory of gravity, where R and ? represent the Ricci scalar and scalar potential respectively. Specifically, we take the spherically symmetric spacetime to disc...The aim of this paper is to investigate modified f(R, ?) theory of gravity, where R and ? represent the Ricci scalar and scalar potential respectively. Specifically, we take the spherically symmetric spacetime to discuss the possible emergence of compact stars. We study the physical behavior of compact stars by considering 4 U 1820-30, SAX J1808-3658 and Her X1, which are three popular models of compact stars. The graphical analysis of energy density, radial pressure, tangential pressure, energy conditions as well as stability of compact stars has been shown. It is concluded that behavior of these three stars is usual for f(R, ?) gravity models with some specific choices of model parameters.展开更多
This paper presents an innovative framework for modeling anisotropic compact stars by incorporating the density profile of Bose-Einstein condensate dark matter within the f(Q)gravity framework.This approach provides n...This paper presents an innovative framework for modeling anisotropic compact stars by incorporating the density profile of Bose-Einstein condensate dark matter within the f(Q)gravity framework.This approach provides new insights into the dynamics of compact stars and the role of dark matter in their structure.We derive the metric potential for compact stellar configurations and calculate the associated unknown parameters.Analyzing the physical properties of the compact star PSR J1614-2230 across various values of k,we find that the derived interior solutions for anisotropic stars satisfy all essential physical conditions,thereby confirming the robustness and stability of the proposed model.展开更多
Recently, Cristofaro-Gardiner and Hutchings proved that there exist at least two closed characteristics on every compact star-shaped hypersuface in R4. Then Ginzburg, Hein, Hryniewicz, and Macarini gave this result a ...Recently, Cristofaro-Gardiner and Hutchings proved that there exist at least two closed characteristics on every compact star-shaped hypersuface in R4. Then Ginzburg, Hein, Hryniewicz, and Macarini gave this result a second proof. In this paper, we give it a third proof by using index iteration theory, resonance identities of closed characteristics and a remarkable theorem of Ginzburg et at.展开更多
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 ex...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 T.In 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 configuration.We 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 SMCX-1.Via 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.展开更多
We present a new class of solutions to the Einstein field equations for an anisotropic matter distribution in which the interior space-time obeys the Karmarkar condition. The necessary and sufficient condition require...We present a new class of solutions to the Einstein field equations for an anisotropic matter distribution in which the interior space-time obeys the Karmarkar condition. The necessary and sufficient condition required for a spherically symmetric space-time to be of Class One reduces the gravitational behavior of the model to a single metric function. By assuming a physically viable form for the grr metric potential we obtain an exact solution of the Einstein field equations which is free from any singularities and satisfies all the physical criteria. We use this solution to predict the masses and radii of well-known compact objects such as Cen X-3, PSR J0348＋0432, PSR B0943＋10and XTE J1739-285.展开更多
In the present study,we investigate the anisotropic stellar solutions admitting Finch-Skea symmetry(viable and non-singular metric potentials)in the presence of some exotic matter fields,such as Bose-Einstein Condensa...In the present study,we investigate the anisotropic stellar solutions admitting Finch-Skea symmetry(viable and non-singular metric potentials)in the presence of some exotic matter fields,such as Bose-Einstein Condensate(BEC)dark matter,the Kalb-Ramond fully anisotropic rank-2 tensor field from the low-energy string theory effective action,and the gauge field imposing U(1)symmetry.Interior spacetime is matched with both Schwarzchild and Reissner-N?rdstrom vacuum spacetimes for BEC,KB,and gauge fields.In addition,we study the energy conditions,Equation of State(EoS),radial derivatives of energy density and anisotropic pressures,Tolman-OppenheimerVolkoff equilibrium condition,relativistic adiabatic index,sound speed,and surface redshift.Most of the aforementioned conditions are satisfied.Therefore,the solutions derived in the current study lie in the physically acceptable regime.展开更多
Topological structure has been extensively studied and confirmed in highly correlated condensed matter physics. We explore the gravitational waves emitted from binary neutron star mergers using the pseudoconformal mod...Topological structure has been extensively studied and confirmed in highly correlated condensed matter physics. We explore the gravitational waves emitted from binary neutron star mergers using the pseudoconformal model for dense nuclear matter for compact stars. This model considers the topology change and the possible emergent scale symmetry and satisfies all the constraints from astrophysics. We find that the location of the topology change affects gravitational waves dramatically owing to its effect on the equation of state. In addition, the effect of this location on the waveforms of the gravitational waves is within the ability of the on-going and up-coming facilities for detecting gravitational waves, thus suggesting a possible way to measure the topology structure in nuclear physics.展开更多
Solving field equations exactly in f(R,T)−gravity is a challenging task.To do so,many authors have adopted different methods such as assuming both the metric functions and an equation of state(EoS)and a metric functio...Solving field equations exactly in f(R,T)−gravity is a challenging task.To do so,many authors have adopted different methods such as assuming both the metric functions and an equation of state(EoS)and a metric function.However,such methods may not always lead to well-behaved solutions,and the solutions may even be rejected after complete calculations.Nevertheless,very recent studies on embedding class-one methods suggest that the chances of arriving at a well-behaved solution are very high,which is inspiring.In the class-one approach,one of the metric potentials is estimated and the other can be obtained using the Karmarkar condition.In this study,a new class-one solution is proposed that is well-behaved from all physical points of view.The 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=1.This 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 J1808.4-3658.Therefore,for different values ofχ,the corresponding radii and their respective moments of inertia have been predicted from the M−I curve.展开更多
F(R)gravity is a modified gravity theory,and its applications for the compact star have attracted attention in the last decades.We review the basics of the F(R)gravity theory and the modified Tolman-Oppenheimer-Volkof...F(R)gravity is a modified gravity theory,and its applications for the compact star have attracted attention in the last decades.We review the basics of the F(R)gravity theory and the modified Tolman-Oppenheimer-Volkoff(TOV)equation.Recent 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 matter.Moreover,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)model.Finally,We discuss the future directions for testing gravitational theories by observational measurements of the compact stars.展开更多
In this paper,we study the third family of compact stars with the color-flavor locked(CFL)quark core.The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter.The results...In this paper,we study the third family of compact stars with the color-flavor locked(CFL)quark core.The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter.The results of the calculation show a transitional behavior that goes from the hadron star range,through the transition range,into the CFL quark star range.In the transition range,the third family of compact stars with the CFL quark matter core is found in the wide range of the CFL energy gap 100MeV≤<150 MeV.By comparing with early investigations,we argue that the greatest possible third family of compact stars may be the hybrid stars with the CFL quark core.展开更多
We present the interior solutions of distributions of magnetized fluid inside a sphere in f（R, T） gravity. Tile magnetized sphere is embedded in an exterior Reissner NordstrOm metric. We assume that all physical qua...We present the interior solutions of distributions of magnetized fluid inside a sphere in f（R, T） gravity. Tile magnetized sphere is embedded in an exterior Reissner NordstrOm metric. We assume that all physical quantities are in static equilibrium. The perfect fluid matter is studied under a particular form of the Lagrangian density f（R, T）. The magnetic field profile in modified gravity is calculated. Observational data of neutron stars are used to plot suitable models of magnetized compact objects. We reveal the effect of f（R, T） gravity on the magnetic field profile, with application to neutron stars, especially highly magnetized neutron stars found in x-ray pulsar systems. Finally, the effective potential Veff and innermost stable circular orbits, arising out of the motion of a test particle of negligible mass influenced by attraction or repulsion from the massive center, are discussed.展开更多
Perturbation methods are employed to calculate time variation in the orbital elements of a compact binary system. It turns out that the semi-major axis and eccentricity exhibit only periodic variations. The longitude ...Perturbation methods are employed to calculate time variation in the orbital elements of a compact binary system. It turns out that the semi-major axis and eccentricity exhibit only periodic variations. The longitude of periastron and mean longitude of epoch exhibit both secular and periodic variation. In addition, the relativistic effects on the time of periastron passage of binary stars are also given. Four compact binary systems (PSRJ0737-3039, PSR1913+16, PSR1543+12 and M33X-7) are considered. Numerical results for both secular and periodic effects are presented, and the possibility of observing them is discussed.展开更多
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. W...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.展开更多
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 J1808.4-3658.The Einstein field equations are solved ...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 J1808.4-3658.The Einstein field equations are solved by assuming that the interior of the compact object is described by a class I spacetime.The so-called Karmarkar condition arising from this requirement is integrated to reduce the gravitational behaviour to a single generating function.By appealing to physics we adopt a form for the gravitational potential which is sufficiently robust to accurately describe compact objects.Our model satisfies all the requirements for physically realistic stellar structures.展开更多
We obtained a new class of solutions for a relativistic anisotropic compact star by utilizing the Karmarkar embedding condition.To obtain the closed-form solution a suitable form of one of the gravitational potentials...We obtained a new class of solutions for a relativistic anisotropic compact star by utilizing the Karmarkar embedding condition.To obtain the closed-form solution a suitable form of one of the gravitational potentials has been chosen to determine the other by analyzing the Karmarkar condition.The resulting solutions are found to be well-behaved and regular and could describe a compact stellar object.Considering the current estimated values of the mass and radius of the pulsar 4U1820-30 as input parameters,all the physically relevant parameters are shown to be well-behaved to a very good degree of accuracy.展开更多
Announcement from Editorial Board The following article has been retracted due to plagiarism. This paper published in Vol.3 No.4, April 2012, has been removed from this site. Title: On the Relativistic Stars Author: S...Announcement from Editorial Board The following article has been retracted due to plagiarism. This paper published in Vol.3 No.4, April 2012, has been removed from this site. Title: On the Relativistic Stars Author: Silvia Morales, Roberto Aquilano It has been brought to our attention that this paper appears exactly as it was published in Astroparticle Physics, vol. 32, 2009, 153. ('On the nature of relativistic stars' by Silvia Morales, Alejandra Zorzi, Roberto Aquilano) Consequently, this paper has been retracted by Journal of Modern Physics. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?JMP Editorial Board ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?April 30,展开更多
文摘In the present article,we introduce a completely new regular model for static,spherically symmetric celestial fluid spheres in embedding classⅠspacetime.In this regard,needfully,we propose a new suitable metric potential e^(λ(r))to generate the present model.The various analyses on energy density,pressure,anisotropic factor,mass,compactness parameter,redshift,and energy condition make sure the model is physically viable on the ground of model stars Vela X-1,Cen X-3,SMC X-4,and LMC X-4.The reported solutions also respect the equilibrium state by satisfying the Tolman-Oppenheimer-Volkoff(TOV)equation and ensure stability by satisfying the causality condition,condition on the adiabatic index,and Harrison-Zeldovich-Novikov condition.The generated M-R graph matches the ranges of masses and radii for the model compact stars.Additionally,this study provides estimates of the moment of inertia based on the I-M graph.
基金Supported by the Fundamental Research Funds for the Central Universities under Grant No ZYGX2009X008
文摘Based on the generalized uncertainty principle with maximum momentum arid minimal length, we discuss the equation of state of ideal ultra-relativistic Fermi gases at zero temperature. Maximum momentum avoids the problem that the Fermi degenerate pressure blows up since the increase of the Fermi energy is not limited. Applying this equation of state to the Tolman-Oppenheimer Volkoff （TOV） equation, the quantum gravitational effects on the cores of compact stars are discussed. In the center of compact stars, we obtain the singularity-free solution of the metric component, gtt ～-（1 ＋ 0.2185×r^2）. By numerically solving the TOV equation, we find that quantum gravity plays an important role in the region r～10^4α0（△x）min. Current observed masses of neutron stars indicate that the dimensionless parameter α0 cannot exceed 10^19.
文摘The effects of gravitomagnetic force on plasma oscillations are investigated using the kinetic theory of homogeneous electrically neutral plasma in the absence of external electric or magnetic field. The random phase assumption is employed neglecting the thermal motion of the electrons with respect to a fixed ion background. It is found that the gravitomagnetic force reduces the characteristic frequency of the plasma thus enhancing the refractive index of the medium. The estimates for the predicted effects are given for a typical white dwarf, pulsar, and neutron star.
基金National University of Computer and Emerging Sciences(NUCES),Pakistan
文摘The aim of this paper is to investigate modified f(R, ?) theory of gravity, where R and ? represent the Ricci scalar and scalar potential respectively. Specifically, we take the spherically symmetric spacetime to discuss the possible emergence of compact stars. We study the physical behavior of compact stars by considering 4 U 1820-30, SAX J1808-3658 and Her X1, which are three popular models of compact stars. The graphical analysis of energy density, radial pressure, tangential pressure, energy conditions as well as stability of compact stars has been shown. It is concluded that behavior of these three stars is usual for f(R, ?) gravity models with some specific choices of model parameters.
基金DST,New Delhi,India,for their infrastructural support for research facilities under DST-FIST-2019。
文摘This paper presents an innovative framework for modeling anisotropic compact stars by incorporating the density profile of Bose-Einstein condensate dark matter within the f(Q)gravity framework.This approach provides new insights into the dynamics of compact stars and the role of dark matter in their structure.We derive the metric potential for compact stellar configurations and calculate the associated unknown parameters.Analyzing the physical properties of the compact star PSR J1614-2230 across various values of k,we find that the derived interior solutions for anisotropic stars satisfy all essential physical conditions,thereby confirming the robustness and stability of the proposed model.
基金partially supported by China Postdoctoral Science Foundation(Grant No.2013M540512)partially supported by NSFC(Grant No.11131004),MCME,LPMC of MOE of China,Nankai University and BCMIIS of Capital Normal University
文摘Recently, Cristofaro-Gardiner and Hutchings proved that there exist at least two closed characteristics on every compact star-shaped hypersuface in R4. Then Ginzburg, Hein, Hryniewicz, and Macarini gave this result a second proof. In this paper, we give it a third proof by using index iteration theory, resonance identities of closed characteristics and a remarkable theorem of Ginzburg et at.
文摘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 T.In 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 configuration.We 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 SMCX-1.Via 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.
文摘We present a new class of solutions to the Einstein field equations for an anisotropic matter distribution in which the interior space-time obeys the Karmarkar condition. The necessary and sufficient condition required for a spherically symmetric space-time to be of Class One reduces the gravitational behavior of the model to a single metric function. By assuming a physically viable form for the grr metric potential we obtain an exact solution of the Einstein field equations which is free from any singularities and satisfies all the physical criteria. We use this solution to predict the masses and radii of well-known compact objects such as Cen X-3, PSR J0348＋0432, PSR B0943＋10and XTE J1739-285.
基金National Board for Higher Mathematics(NBHM)under Department of Atomic Energy(DAE)Govt.of India for financial support to carry out the Research project No.:02011/3/2022 NBHM(R.P.)/R#D II/2152 Dt.14.02.2022Sokoliuk O.performed the work in frame of the"Mathematical modeling in interdisciplinary research of processes and systems based on intelligent supercomputer,grid and cloud technologies"program of the NAS of Ukraine。
文摘In the present study,we investigate the anisotropic stellar solutions admitting Finch-Skea symmetry(viable and non-singular metric potentials)in the presence of some exotic matter fields,such as Bose-Einstein Condensate(BEC)dark matter,the Kalb-Ramond fully anisotropic rank-2 tensor field from the low-energy string theory effective action,and the gauge field imposing U(1)symmetry.Interior spacetime is matched with both Schwarzchild and Reissner-N?rdstrom vacuum spacetimes for BEC,KB,and gauge fields.In addition,we study the energy conditions,Equation of State(EoS),radial derivatives of energy density and anisotropic pressures,Tolman-OppenheimerVolkoff equilibrium condition,relativistic adiabatic index,sound speed,and surface redshift.Most of the aforementioned conditions are satisfied.Therefore,the solutions derived in the current study lie in the physically acceptable regime.
基金supported by the National Natural Science Foundation of China(Grant Nos.11875147,and 11475071)supported by the National Natural Science Foundation of China(Grant Nos.11851302,11851303,11690022,and 11747601)+2 种基金the Intensive Study of Future Space Science Missions of the Strategic Priority Program on Space Sciencethe Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB23030100)the CAS Center for Excellence in Particle Physics(CCEPP)。
文摘Topological structure has been extensively studied and confirmed in highly correlated condensed matter physics. We explore the gravitational waves emitted from binary neutron star mergers using the pseudoconformal model for dense nuclear matter for compact stars. This model considers the topology change and the possible emergent scale symmetry and satisfies all the constraints from astrophysics. We find that the location of the topology change affects gravitational waves dramatically owing to its effect on the equation of state. In addition, the effect of this location on the waveforms of the gravitational waves is within the ability of the on-going and up-coming facilities for detecting gravitational waves, thus suggesting a possible way to measure the topology structure in nuclear physics.
文摘Solving field equations exactly in f(R,T)−gravity is a challenging task.To do so,many authors have adopted different methods such as assuming both the metric functions and an equation of state(EoS)and a metric function.However,such methods may not always lead to well-behaved solutions,and the solutions may even be rejected after complete calculations.Nevertheless,very recent studies on embedding class-one methods suggest that the chances of arriving at a well-behaved solution are very high,which is inspiring.In the class-one approach,one of the metric potentials is estimated and the other can be obtained using the Karmarkar condition.In this study,a new class-one solution is proposed that is well-behaved from all physical points of view.The 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=1.This 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 J1808.4-3658.Therefore,for different values ofχ,the corresponding radii and their respective moments of inertia have been predicted from the M−I curve.
文摘F(R)gravity is a modified gravity theory,and its applications for the compact star have attracted attention in the last decades.We review the basics of the F(R)gravity theory and the modified Tolman-Oppenheimer-Volkoff(TOV)equation.Recent 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 matter.Moreover,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)model.Finally,We discuss the future directions for testing gravitational theories by observational measurements of the compact stars.
基金supported by the National Natural Science Foundation of China(10675024,11075063,11265009)National Fund for Fostering Talents of Basic Science (J1103202)
文摘In this paper,we study the third family of compact stars with the color-flavor locked(CFL)quark core.The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter.The results of the calculation show a transitional behavior that goes from the hadron star range,through the transition range,into the CFL quark star range.In the transition range,the third family of compact stars with the CFL quark matter core is found in the wide range of the CFL energy gap 100MeV≤<150 MeV.By comparing with early investigations,we argue that the greatest possible third family of compact stars may be the hybrid stars with the CFL quark core.
文摘We present the interior solutions of distributions of magnetized fluid inside a sphere in f（R, T） gravity. Tile magnetized sphere is embedded in an exterior Reissner NordstrOm metric. We assume that all physical quantities are in static equilibrium. The perfect fluid matter is studied under a particular form of the Lagrangian density f（R, T）. The magnetic field profile in modified gravity is calculated. Observational data of neutron stars are used to plot suitable models of magnetized compact objects. We reveal the effect of f（R, T） gravity on the magnetic field profile, with application to neutron stars, especially highly magnetized neutron stars found in x-ray pulsar systems. Finally, the effective potential Veff and innermost stable circular orbits, arising out of the motion of a test particle of negligible mass influenced by attraction or repulsion from the massive center, are discussed.
文摘Perturbation methods are employed to calculate time variation in the orbital elements of a compact binary system. It turns out that the semi-major axis and eccentricity exhibit only periodic variations. The longitude of periastron and mean longitude of epoch exhibit both secular and periodic variation. In addition, the relativistic effects on the time of periastron passage of binary stars are also given. Four compact binary systems (PSRJ0737-3039, PSR1913+16, PSR1543+12 and M33X-7) are considered. Numerical results for both secular and periodic effects are presented, and the possibility of observing them is discussed.
基金supported by the Cultivating Plan of Characteristic Direction of Science(2020SCUNL209)。
文摘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.
文摘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 J1808.4-3658.The Einstein field equations are solved by assuming that the interior of the compact object is described by a class I spacetime.The so-called Karmarkar condition arising from this requirement is integrated to reduce the gravitational behaviour to a single generating function.By appealing to physics we adopt a form for the gravitational potential which is sufficiently robust to accurately describe compact objects.Our model satisfies all the requirements for physically realistic stellar structures.
文摘We obtained a new class of solutions for a relativistic anisotropic compact star by utilizing the Karmarkar embedding condition.To obtain the closed-form solution a suitable form of one of the gravitational potentials has been chosen to determine the other by analyzing the Karmarkar condition.The resulting solutions are found to be well-behaved and regular and could describe a compact stellar object.Considering the current estimated values of the mass and radius of the pulsar 4U1820-30 as input parameters,all the physically relevant parameters are shown to be well-behaved to a very good degree of accuracy.
文摘Announcement from Editorial Board The following article has been retracted due to plagiarism. This paper published in Vol.3 No.4, April 2012, has been removed from this site. Title: On the Relativistic Stars Author: Silvia Morales, Roberto Aquilano It has been brought to our attention that this paper appears exactly as it was published in Astroparticle Physics, vol. 32, 2009, 153. ('On the nature of relativistic stars' by Silvia Morales, Alejandra Zorzi, Roberto Aquilano) Consequently, this paper has been retracted by Journal of Modern Physics. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?JMP Editorial Board ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?April 30,
