An electromagnetic extension of the Schwarzschild interior solution and the corresponding Buchdahl limit

We wish to construct a model for charged star as a generalization of the uniform density Schwarzschild interior solution. We employ the Vaidya and Tikekar ansatz (Astrophys Astron 3:325, 1982) for one of the metric potentials and electric field is chosen in such a way that when it is switched off the metric reduces to the Schwarzschild. This relates charge distribution to the Vaidya–Tikekar parameter, k, indicating deviation from sphericity of three dimensional space when embedded into four dimensional Euclidean space. The model is examined against all the physical conditions required for a relativistic charged fluid sphere as an interior to a charged star. We also obtain and discuss charged analogue of the Buchdahl compactness bound.

Charged stellar structure in Tolman–Kuchowicz spacetime

In this paper, we have presented the Einstein–Maxwell equations which are described by the spherically symmetric spacetime in the presence of charge by exploiting the Tolman–Kuchowicz spacetime. The corresponding field equations are constructed and the form of charge distribution is chosen to be [Formula: see text], where [Formula: see text] is a constant quantity. We also find the values of unknown constants from junction conditions and discuss the behavior of effective energy density, effective radial and tangential pressure and anisotropic factor with two viable [Formula: see text] models. We examine the physical stability of charged stellar structure through energy conditions, causality and stability condition. We use modified form of TOV equation for anisotropic charged fluid sphere to analyze the equilibrium condition. In this work, we model the compact star candidate SAXJ 1808.4 – 3658 and study the compactness level and anisotropic behavior corresponding to the variation of physical parameters which are involved in [Formula: see text] models. Further, we evaluate some important properties such as mass-radius ratio compactness factor and surface redshift. It is depicted from this study that the obtained solutions provide strong evidences for more realistic and viable stellar model.

Analytical studies on the hoop conjecture in charged curved spacetimes

Recently, with numerical methods, Hod clarified the validity of Thorne hoop conjecture for spatially regular static charged fluid spheres, which were considered as counterexamples against the hoop conjecture. In this work, we provide an analytical proof on Thorne hoop conjecture in the spatially regular static charged fluid sphere spacetimes.

Anisotropic Charged Fluid Sphere in Isotropic Coordinates

We have presented a class of charged superdense star models, starting with a static spherically symmetric metric in isotropic coordinates for anisotropic fluid by considering Hajj-Boutros-(1986) type metric potential and a specific choice of electrical intensity E and anisotropy factor Δ which involve charge parameter K and anisotropy parameter α. The solution is well behaved for all the values of Schwarzschild compactness parameter u lying in the range 0<u≤0.2086, for all values of charge parameter K lying in the range 0.04≤K≤0.111 , and for all values of anisotropy parameter α lying in the range 0.016≥α≥0. With the increase in α, the values of K and u decrease. Further, we have constructed a superdense star model with all degree of suitability. The solution so obtained is utilized to construct the models for superdense star like neutron stars ρb=2.7×1014 g/cm3 and strange quark stars ρb=4.6888×1014 g/cm3 . For K=0.06 and α=0.01, the maximum mass of neutron star is observed as M=1.53 M⊙ and radius R=11.48 km. Further for strange quark stars M=1.16 M⊙ and R=8.71 km are obtained.

ISOTROPIC CASES OF STATIC CHARGED FLUID SPHERES IN GENERAL RELATIVITY

In this paper we study the isotropic cases of static charged fluid spheres in general relativity. For this purpose we consider two different specializations and under these we solve the Einstein–Maxwell field equations in isotropic coordinates. The analytical solutions thus obtained are matched to the exterior Reissner–Nordström solutions which concern the values for the metric coefficients eν and eμ. We derive the pressure, density and pressure-to-density ratio at the center of the charged fluid sphere and boundary R of the star. Our conclusion is that static charged fluid spheres provide a good connection to compact stars.