Anisotropic stellar model of neutron stars in f(T) gravity with off-diagonal tetrad

In this paper, we develop a new class of analytical solutions describing anisotropic stellar structures of observed neutron stars using modified f(T) gravity. We use the off-diagonal tetrad that is best suitable for studying spherically symmetric objects in f(T) gravity. We develop exact solutions in the quadratic model of f(T) gravity by introducing physically reliable metric potentials that can describe a wide range of astrophysical systems. We then apply the model to investigate the stellar structures of four observed compact stars, 4U 1538-52, J0437-4715, J0030+0451, and 4U 1820-30. We calculate the values of model parameters for the stellar objects under examination in this paper. Comprehensive graphical analysis shows that the model describing anisotropic stellar structures is physically acceptable, causal, and stable. The model inherently exhibits the quadratic equation of state that can be utilized to investigate the material composition and stellar structures of the observed compact stars.

Charged stellar model with three layers

We establish new charged stellar models from the Einstein-Maxwell field equations for relativistic superdense objects outfitted with three layers. The core layer is described by a linear equation of state (EoS) describing quark matter, while the intermediate layer is described by a Bose-Einstein condensate EoS for Bose-Einstein condensate matter and the envelope layers satisfying a quadratic EoS for the neutron fluid. We have specified a new choice of the electric field and one of the metric potentials. It is interesting to note that the choice of electric field in this model can be set to vanish and we can regain earlier neutral models. Plots generated depict that the matter variables, gravitational potentials and other physical conditions are consistent with astrophysical studies. The interior layers and exterior boundary are also matched.

Exploring physical features of anisotropic quark stars in Brans-Dicke theory with a massive scalar field via embedding approach

The main aim of this manuscript is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity. The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions by using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks. We use a well-behaved function along with Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors. The radii of the strange compact stars viz., PSR J1416-2230, PSR J1903+327, 4U 1820-30, CenX-3, EXO1785-248 are predicted via their observed mass for different values of the massive Brans-Dicke parameters. We explore the influences of mass of scalar field $m_{\phi}$ as well as coupling parameter $\omega_{BD}$ along with bag constant $\mathcal{B}$ on state determinants and perform several tests on the viability and stability of the constructed stellar model. Conclusively, we find that our stellar system is physically viable and stable as it satisfies all the energy conditions as well as necessary stability criteria under the influence of a gravitational scalar field.

A Relativistic Compact Stellar Model of Anisotropic Quark Matter Mixed with Dark Energy

The possibility of strange stars mixed with dark energy to be one of the candidates for dark energy stars is the main issue of the present study. Our investigation shows that quark matter atcs as dark energy after a certain yet unknown critical condition inside the quark stars. Our proposed model reveals that strange stars mixed with dark energy feature a physically acceptable stable model and mimic characteristics of dark energy stars. The plausible connections are shown through the mass-radius relation as well as the entropy and temperature. We particularly note that a two-fluid distribution is a major reason for the anisotropic nature of the spherical stellar system.

Chaplygin strange stars in presence of quintessence

Starting from a regular, static and spherically symmetric spacetime, we present a stellar model formed by two sources of ordinary and quintessence matter both with anisotropic pressures. The ordinary matter, with density [Formula: see text], is formed by a fluid with a state equation type Chaplygin [Formula: see text] for the radial pressure. And the quintessence matter, with density [Formula: see text], has a state equation [Formula: see text] for the radial pressure and [Formula: see text] for the tangential pressure with [Formula: see text]. The model satisfies the required conditions to be physically acceptable and additionally the solution is potentially stable, i.e. [Formula: see text] according to the cracking concept, and it also satisfies the Harrison–Zeldovich–Novikov criteria. We describe in a graphic manner the behavior of the solution for the case in which the mass is [Formula: see text] and radius [Formula: see text][Formula: see text]km which matches the star EXO 1785-248, from where we obtain the maximum density [Formula: see text] for the values of the parameters [Formula: see text], [Formula: see text].

An anisotropic charged fluids with Chaplygin equation of state

A stellar model with an electrically charged anisotropic fluid as a source of matter is presented. The radial pressure is described by a Chaplygin state equation, [Formula: see text], while the anisotropy [Formula: see text] is annulled in the center of the star [Formula: see text] is regular and [Formula: see text], the electric field, is also annulled in the center. The density pressures and the tangential speed of sound are regular, while the radial speed of sound is monotonically increasing. The model is physically acceptable and meets the stability criteria of Harrison–Zeldovich–Novikov and in respect of the cracking concept the solution is unstable in the region of the center and potentially stable near the surface. A graphic description is presented for the case of an object with a compactness rate [Formula: see text], mass [Formula: see text] and radius [Formula: see text] km that matches the star Vela X-1. Also, the interval of the central density [Formula: see text], which is consistent with the expected magnitudes for this type of stars, which shows that the behavior is accurate for describing compact objects.