Article
Physics, Multidisciplinary
H. Alrebdi, Abdelghani Errehymy, Ksh Newton Singh, G. Mustafa, Abdel-Haleem Abdel-Aty, Mohammed Daoud
Summary: This article introduces a self-bound quark star model with net electric charge and compares it to four compact stars. The models satisfy various conditions and predict the radii of the compact objects.
Article
Astronomy & Astrophysics
A. S. Lighuda, S. D. Maharaj, J. M. Sunzu, E. W. Mureithi
Summary: New exact solutions to the Einstein-Maxwell field equations for charged anisotropic stellar objects with three interior layers are generated in this study. These charged stellar models comprise three interior layers with specified equations of state. Graphs are plotted to demonstrate that the matter, gravitational potentials, and other physical conditions are consistent with astrophysical studies. A notable feature is that the outer layer satisfies the Chaplygin equation of state.
ASTROPHYSICS AND SPACE SCIENCE
(2021)
Article
Physics, Multidisciplinary
Iwo Bialynicki-Birula, Zofia Bialynicka-Birula, Szymon Augustynowicz
Summary: Contrary to many authors' statements, backflow is not a nonclassical effect, but rather a characteristic feature of solutions to wave equations (both quantum and classical).
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2022)
Article
Physics, Multidisciplinary
J. W. Jape, J. M. Sunzu, S. D. Maharaj, J. M. Mkenyeleye
Summary: Exact solutions of charged anisotropic fluid spheres with a linear equation of state are generated by incorporating conformal symmetry and an equation of state. These solutions satisfy several important physical conditions, including smooth matching, compatibility with observations, and stability requirement.
INDIAN JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
Alberto K. Mathias, Jefta M. Sunzu, Sunil D. Maharaj, Jason M. Mkenyeleye
Summary: Exact solutions for charged relativistic anisotropic stars are generated using the Karmarkar condition with Einstein-Maxwell field equations and a linear equation of state. The Bannerji and Durgapal transformation is employed to transform the nonlinear differential equations and field equations. The embedding approach provides a relationship between gravitational potentials, helping to solve and integrate the field equations. The detailed physical analysis shows that the model satisfies necessary conditions such as stability, equilibrium, energy conditions, and the mass-radius relationship.
PRAMANA-JOURNAL OF PHYSICS
(2023)
Article
Astronomy & Astrophysics
V. S. Manko, E. Ruiz
Summary: In this paper, two physically meaningful configurations of a pair of equal Kerr-Newman corotating black holes separated by a massless strut are elaborated using the general equatorially symmetric two-soliton solution. The thermodynamic properties of these binary configurations are studied and the first law of thermodynamics taking correctly into account the magnetic field contribution is formulated for each case.
Article
Physics, Particles & Fields
Marco Astorino, Adriano Vigano
Summary: In this paper, we study multi-black hole systems immersed in external gravitational field configurations in four-dimensional General Relativity. By using an infinite multipolar expansion, the conical singularities of a series of collinear static black holes are regularized. We also achieve a stationary rotating black hole system by adding independent angular momenta and NUT parameters to each source of the binary configuration. Furthermore, a charged extension of the binary black hole system at equilibrium is generated. Lastly, we demonstrate the consistent recovery of the binary Majumdar-Papapetrou solution in the vanishing external field limit.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
Fredrick W. Cotton
Summary: The proposed modifications to the Einstein-Maxwell equations include adding a scalar term and a four-dimensional nonlinear electromagnetic constitutive tensor, introducing additional curvature terms and a non-isotropic pressure tensor. These modifications allow for coupling between particle solutions, localized electromagnetic and gravitational wave solutions, and differentiate between Schwarzschild mass and inertial mass.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Physics, Multidisciplinary
Avirt S. Lighuda, Sunil D. Maharaj, Jefta M. Sunzu, Eunice W. Mureithi
Summary: In this study, we propose a new exact model for dense stellar objects with three distinct interior regions, each described by a different equation of state. Our model is supported by a physical analysis and well-behaved matter variables, metric functions, and other physical conditions. The matching of boundary layers is accomplished with the help of the Reissner-Nordstrom exterior space-time.
PRAMANA-JOURNAL OF PHYSICS
(2022)
Article
Astronomy & Astrophysics
Gerard Clement, Dmitri Galtsov
Summary: In the framework of Einstein-Maxwell theory, we consider collinear arrays of rotating electrically charged black holes connected by Misner-Dirac strings. The first law of mechanics for these systems is derived, and the variations under different conditions are discussed.
Article
Astronomy & Astrophysics
Han Rui Fu, Jia Jie Li, Armen Sedrakian, Fridolin Weber
Summary: A set of hyperonic equations of state (EoS) are constructed by assuming SU(3) symmetry and using a covariant density functional theory approach. The EoS is constrained by terrestrial experiments at low density and modeled by varying the nuclear matter skewness coefficient and symmetry energy slope at high density. The results show that the model can support a range of static and rotating stellar masses under certain conditions.
Article
Physics, Multidisciplinary
J. W. Jape, S. D. Maharaj, J. M. Sunzu, J. M. Mkenyeleye
Summary: We generate charged anisotropic exact models with a conformal Killing vector for static spacetime, which satisfies various physical requirements and regains some known solutions.
INDIAN JOURNAL OF PHYSICS
(2023)
Article
Physics, Particles & Fields
Hector Hernandez, Daniel Suarez-Urango, Luis A. Nunez
Summary: An algorithm is proposed to generate exact anisotropic solutions from a barotropic equation of state by setting an ansatz on the metric functions. The method is illustrated using a generalization of the polytropic equation of state, resulting in two models that meet physical acceptability criteria. It is shown that some relativistic anisotropic polytropic models may have singular tangential sound velocity for polytropic indexes greater than one, while the generalized polytropic equation of state avoids this issue.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Particles & Fields
Amit Kumar Prasad, Mahesh Kumar, Jitendra Kumar
Summary: In this study, a new relativistic anisotropic Einstein field equations solution for compact stars under embedding class 1 conditions is investigated using the Karmarkar condition and the embedding class one technique. The precise analytical solution, taking Buchdahl type metric potential grr into consideration, is explored along with the physical characteristics of various compact star using this analytical solution. The absence of central singularities in the solution is observed. The thermodynamic observables inside the stellar models, including radial and tangential pressures, matter density, anisotropic factor, energy conditions, TOV, red-shift, and the speed of sound, are explored after establishing the space-time geometry for the stellar models. The graphical representation of various physical characteristics demonstrates that the model meets all the specification for ultra-high density compact bodies.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Mathematics, Applied
Joerg Weber
Summary: The time evolution of collisionless plasma is modeled using the relativistic Vlasov-Maxwell system, coupling the Vlasov equation with Maxwell equations. Different particle species and external currents are considered, with weak solution concept introduced to prove the existence of global-in-time solutions.
MATHEMATICAL METHODS IN THE APPLIED SCIENCES
(2021)
Article
Astronomy & Astrophysics
B. C. Paul, A. Chanda, A. Beesham, S. D. Maharaj
Summary: This article investigates cosmological models in f(R) modified gravity with coupled Gauss-Bonnet terms. The evolution of the universe is obtained using numerical techniques, and the presence of dark energy and the oscillation properties of parameters are studied. The results show that under certain interaction strengths, the cosmological parameters can exhibit non-singular oscillation characteristics, and the gravitational coupling constant plays an important role. Additionally, in the presence of interactions, energy from the radiation sector cannot flow to other sectors.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Physics, Particles & Fields
Noeleen Naidoo, Sunil D. Maharaj, Keshlan S. Govinder
Summary: The relationship between radiating stars and Riccati equations in general relativity is examined, considering a general matter distribution including the electromagnetic field and the cosmological constant. A generalized transformation for describing the gravitational potentials of a spherically symmetric relativistic gravitating fluid is introduced, leading to a new Riccati equation at the surface of the radiating star. Exact solutions satisfying the boundary condition are obtained, and the gravitational potentials are explicitly given. Some consistency conditions are reduced to Bernoulli equations, allowing for exact solutions. It is also shown that reducing the order enables the boundary condition to be expressed as a first order equation using the generalized transformation. Solutions obtained using the generalized transformation also satisfy a linear equation of state.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Mathematical
Chevarra Hansraj, Rituparno Goswami, Sunil D. D. Maharaj
Summary: In this paper, we study conformally symmetric generalized Vaidya spacetimes with composite null dust and null string matter distribution using a decomposition method. Our analysis reveals that the geometric variables related to both time-like and preferred space-like congruences are completely determined by the conformal vector and conformal factor. This uniqueness arises from the specific matter distribution of the generalized Vaidya configuration. Additionally, we demonstrate that a proper conformal Killing vector cannot be admitted in the case of pure null dust (or Vaidya) spacetime.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Physics, Multidisciplinary
Noeleen Naidoo, Sunil D. Maharaj, Keshlan S. Govinder
Summary: A model of a radiating star undergoing gravitational collapse is constructed by studying the boundary condition and equation of state. New classes of exact solutions with acceleration, expansion and shear in the presence of the cosmological constant are obtained. The range of the equation of state parameters allows the solution to be interpreted as barotropic matter stars or dark energy stars. The model is physically reasonable and satisfies the energy conditions.
Article
Astronomy & Astrophysics
Byron P. Brassel, Sunil D. Maharaj, Rituparno Goswami
Summary: The junction conditions for a higher dimensional spherically symmetric charged and anisotropic static star in Einstein-Gauss-Bonnet (EGB) gravity with nonvanishing cosmological constant are derived. It is shown that the generalised matching conditions are satisfied across the timelike boundary hypersurface of zero thickness in EGB gravity. The validity of Israel-Darmois conditions is a sufficient condition for the matching. Therefore, a complete stellar model can be generated in EGB gravity. The interior matches to the exterior higher dimensional charged Boulware-Deser spacetime with cosmological constant. The vanishing of barotropic radial pressure at the boundary of the star is also consistent with general relativity.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
Shavani Naicker, Sunil D. Maharaj, Byron P. Brassel
Summary: In this study, we investigated the influence of higher order curvature terms on the static configuration of a charged dust distribution in EGB gravity. We found exact solutions to the governing equations using special functions, series, and polynomials. The results show that the charged dust model behaves well in the center region and can generate dust spheres. The higher order curvature terms have a distinct influence on the dynamics of charged dust and gravitational behavior compared to general relativity.
GENERAL RELATIVITY AND GRAVITATION
(2023)
Article
Physics, Particles & Fields
Shavani Naicker, Sunil D. Maharaj, Byron P. Brassel
Summary: In this paper, the field equations for a charged gravitating perfect fluid in Einstein-Gauss-Bonnet gravity are derived in all spacetime dimensions. The static and spherically symmetric spacetime leads to a charged condition of pressure isotropy, which is a second-order Abel differential equation. It is shown that this equation can be simplified to a first-order, nonlinear canonical differential equation in higher dimensions. The canonical form allows for an exact solution generating algorithm, resulting in implicit solutions by choosing potentials and the electromagnetic field. An exact solution to the canonical equation is found, which corresponds to the neutral model previously discovered. Additionally, three new classes of solutions are obtained by placing constraints on the canonical differential equation, without specifying gravitational potentials and electromagnetic field. When the canonical form is not applicable, other classes of exact solutions are presented using elementary and special functions (the Heun confluent functions).
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
C. Hansraj, R. Goswami, S. D. Maharaj
Summary: In this paper, the Kerr spacetime is analyzed using a semi-tetrad decomposition. The 1+1+2 covariant method is applied to describe the geometry of the Kerr spacetime outside the horizon. A comparison is made between observers in the Killing frame and the ZAMO frame, resulting in different geometrical quantities and equations. This novel approach provides new insights into the Kerr spacetime geometry in a transparent manner.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Sunil D. Maharaj, Noeleen Naidoo, Gareth Amery, Keshlan S. Govinder
Summary: The Karmarkar embedding condition in different spherically symmetrical metrics is studied using Lie symmetries. The study extends recent results by investigating the Lie symmetries for conformally flat and shear-free metrics. Additionally, the Lie symmetries for geodesic metrics and general spherical spacetimes are obtained for the first time. The study also demonstrates that the Karmarkar condition can be used to produce an embeddable relativistic radiating star with a barotropic equation of state via Lie symmetries.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Noeleen Naidoo, Sunil D. Maharaj, Keshlan S. Govinder
Summary: The objective of this study is to investigate spherically symmetric radiating stars undergoing gravitational collapse, in higher dimensional general relativity, inclusive of acceleration, expansion, shear, an electromagnetic field and a cosmological constant. Two approaches are studied to obtain exact solutions to the boundary condition with/without a linear equation state. Transformations that map the boundary condition into a new Riccati equation are investigated to obtain new exact models. The importance of these transformations in reducing the order of the boundary condition and obtaining new solutions is shown.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Multidisciplinary
Alberto K. Mathias, Jefta M. Sunzu, Sunil D. Maharaj, Jason M. Mkenyeleye
Summary: Exact solutions for charged relativistic anisotropic stars are generated using the Karmarkar condition with Einstein-Maxwell field equations and a linear equation of state. The Bannerji and Durgapal transformation is employed to transform the nonlinear differential equations and field equations. The embedding approach provides a relationship between gravitational potentials, helping to solve and integrate the field equations. The detailed physical analysis shows that the model satisfies necessary conditions such as stability, equilibrium, energy conditions, and the mass-radius relationship.
PRAMANA-JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
J. W. Jape, S. D. Maharaj, J. M. Sunzu, J. M. Mkenyeleye
Summary: We generate charged anisotropic exact models with a conformal Killing vector for static spacetime, which satisfies various physical requirements and regains some known solutions.
INDIAN JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
J. W. Jape, J. M. Sunzu, S. D. Maharaj, J. M. Mkenyeleye
Summary: Exact solutions of charged anisotropic fluid spheres with a linear equation of state are generated by incorporating conformal symmetry and an equation of state. These solutions satisfy several important physical conditions, including smooth matching, compatibility with observations, and stability requirement.
INDIAN JOURNAL OF PHYSICS
(2023)
Article
Physics, Particles & Fields
Byron P. Brassel, Sunil D. Maharaj, Rituparno Goswami
Summary: We generalize the collapse of a spherically symmetric radiation shell with an electromagnetic field in five-dimensional Einstein-Gauss-Bonnet gravity. The presence of charge significantly affects the collapse dynamics, leading to the emergence of a branch singularity separating the physical spacetime from the complex region. We show that this difference in singularity formation is unique to five dimensions, as in higher dimensions the charged collapse terminates with the same branch singularity as in five dimensions. The comparison with charged radiation collapse in general relativity is also provided.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Particles & Fields
Shobhit Giri, Hemwati Nandan, Lokesh Kumar Joshi, Sunil D. Maharaj
Summary: This study examines the stability of circular orbits in a traversable wormhole spacetime and employs the Lyapunov stability approach to determine the motion characteristics of non-spinning test particles in this spacetime.
EUROPEAN PHYSICAL JOURNAL C
(2022)
