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The spherically symmetric dark energy (DE) stellar model is presented here within the context of the f ( Q ) theory of gravity. In order to develop the model, we take into account the linear functional form of f ( Q ) as f ( Q ) = m Q + n , where m is the coupling parameter and n is a real constant. We further assume that the stellar model is composed of normal baryonic matter along with DE; however, for the sake of simplicity, we avoid the interaction between them. The impact of the coupling parameter m on different physical parameters of DE stars (DESs) has been thoroughly investigated. For various values of m specified in the figure, the numerical values of the physical parameters are shown in tabular form. It is found that as m increases, the DES candidates become gradually massive and larger in size. In order to compare the behaviour of DESs with the observational results, we use the measurement of the GW190814 event and the three NS pulsars, viz. 4U1608-52 (mass = 1 . 74 - 0.14 + 0.14 M ⊙ ), PSR J1614-2230 (mass = 1 . 97 - 0.04 + 0.04 M ⊙ ), and PSR J0952-0607 (mass = 2 . 35 - 0.17 + 0.17 M ⊙ ). With the help of the M - R plot, the maximum mass of the DES obtained from our model is 2.57 M ⊙ , which is located within the lower “mass gap” range. To cover the observational constraints, this DES can be a representative for the secondary component of the GW190814 event, whose mass range is detected to be 2 . 59 - 0.09 + 0.08 M ⊙ by LIGO/VIRGO experiments.

Inspired by the conundrum of the gravitational event GW190814, which brings to light the coalescence of a 23 M ⊙ black hole with a yet-to-be-determined secondary component, we look to modeling compact objects within the framework of f() gravity by employing the method of gravitational decoupling. We impose a quadratic equation of state (EOS) for the interior matter distribution, which in the appropriate limit reduces to the MIT bag model. The governing field equations arising from gravitational decoupling bifurcate into the ρ=θ00 and pr=θ11 sectors, leading to two distinct classes of solutions. Both families of solutions are subjected to rigorous tests, qualifying them to describe a plethora of compact objects, including neutron stars, strange stars, and the possible progenitor of the secondary component of GW190814. Using observational data of mass–radius relations for compact objects LMC X-4, Cen X-3, PSR J1614–2230, and PSR J0740+6620, we show that it is possible to generate stellar masses and radii beyond 2.0 M ⊙ for neutron stars. Our findings reveal that the most suitable and versatile model in this framework is the quadratic EOS, which accounts for a range of low-mass stars and typical stellar candidates describing the secondary component of GW190814.

Under general relativity, the paths of accelerated test particles are taken into account. It is examined whether such accelerations have any influence on the ‘singularity’ of the spacetime. The Raychaudhuri equation for the congruence of the time-like curves describing the paths of the accelerated particles is considered to calculate a few physical attributes. It is shown that if the acceleration of the test particles exceeds a particular value, then the congruences of the accelerated time-like curves do not encounter any singularity although the usual energy conditions are violated or modified. It is shown further that in the curved spacetime of general relativistic framework one may generate a system of transformations that is a generalization of the Rindler coordinates related to accelerated frame in the flat Minkowski spacetime. To show the influence of the acceleration of test particle on singularity of a particular spacetime the Schwarzschild spacetime is considered. Taking tidal deviation related acceleration term, it is shown that the acceleration may attain a specific value for which the modified Kretschmann scalar vanishes in a spherical neighbourhood of the singularity and thus the Schwarzschild singularity disappears. In the context of singularity as ‘geodesic incompleteness’ of the spacetime manifold it is also proved that prescribing an appropriate acceleration term on the maximal geodesic defined in a finite interval one may extend it up to infinite proper time and hence the spacetime becomes singularity free. Such results hold at the price of violating the usual energy conditions.

We present herein a new class of singularity-free interior solutions to describe realistic anisotropic compact stellar objects with spherically symmetric matter distribution. A specific form of anisotropy is assumed to obtain the exact solution for the field equation. Smooth matching of interior solutions thus obtained with the Schwarzschild exterior metric over the bounding surface of a compact star, together with the condition that the radial pressure vanishes at the boundary, is used to obtain the mathematical form for the model parameters. The pulsar 4U1608-52 with its current estimated data (mass  = 1.57 M ⊙ and radius = 9.8 ± 0.8  km; Özel et al. in ApJ 820:28, 2016) is used to study the model graphically.

In the current article, we study anisotropic spherically symmetric strange star under the background of f ( R ,  T ) gravity using the metric potentials of Tolman–Kuchowicz type (Tolman in Phys Rev 55:364, 1939; Kuchowicz in Acta Phys Pol 33:541, 1968) as λ ( r ) = ln ( 1 + a r 2 + b r 4 ) and ν ( r ) = B r 2 + 2 ln C which are free from singularity, satisfy stability criteria and also well-behaved. We calculate the value of constants a , b , B and C using matching conditions and the observed values of the masses and radii of known samples. To describe the strange quark matter (SQM) distribution, here we have used the phenomenological MIT bag model equation of state (EOS) where the density profile ( ρ ) is related to the radial pressure ( p r ) as p r ( r ) = 1 3 ( ρ - 4 B g ) . Here quark pressure is responsible for generation of bag constant B g . Motivation behind this study lies in finding out a non-singular physically acceptable solution having various properties of strange stars. The model shows consistency with various energy conditions, TOV equation, Herrera’s cracking condition and also with Harrison–Zel ′ dovich–Novikov’s static stability criteria. Numerical values of EOS parameter and the adiabatic index also enhance the acceptability of our model.

In the present work we study the geodesic motion and accretion process of a test particle near an Anti-de Sitter (ADS) BH surrounded by a dark fluid with a Chaplygin-like equation. Within the defined paradigm, we investigate on the equatorial plane and examine circular geodesics along with their features related to stabilities, radiation energy flux, oscillations and orbits. The general form of the fluid accretion onto the AdS BH through dynamical analysis and mass expansion also has discussed in a depth. Additionally, a few more interesting topics, e.g. the effective potential, angular momentum, specific energy, radiation energy and epicyclic frequencies have also been examined thoroughly. All the attributes are physically acceptable within the observational signatures and ranges.

Quantum mechanical concept such as the Casimir effect is explored to model traversable wormholes in an extended symmetric teleparallel gravity theory. The minimal length concept leading to the generalized uncertainty principle (GUP) is used to obtain the Casimir energy density. The effect of the GUP correction in the geometrical and physical properties of traversable Casimir wormholes are investigated. It is noted that the GUP correction has a substantial effect on the wormhole geometry and it modifies the energy condition. From a detailed calculation of the exotic matter content of the GUP corrected Casimir wormhole, it is shown that, a minimal amount of exotic matter is sufficient to support the stability of the wormhole.

We investigate the dynamics of test particles around a spherically symmetric, non-rotating, hairy regular black hole, examining how the model parameters affect particle motion. The black hole is characterized by two parameters, the mass M and a hairy parameter α . Using the effective potential, we examine the stability of circular orbits. We derive analytical expressions for the energy and angular momentum of test particles as a function of the black hole parameters. The effective forces acting on particles and the innermost stable circular orbits are also examined. Additionally, we numerically integrate the equations of motion to examine particle trajectories and further investigate their motion. Epicyclic oscillations of test particles close to the equatorial plane are explored, and analytical expressions for radial, vertical, and orbital frequencies are derived as functions of the black hole parameters. We also examine the frequency of periastron precession of the particles. We compare the motion of test particles around a hairy regular black hole with the particle motion around a classical non-rotating Schwarzschild black hole. Further, we discuss thermally fluctuating phenomena by using the Tsallis entropy and the energy emission process. Our findings show that the black hole model’s parameters significantly impact particle motion and thermal features.

We present a rigorous study of compact objects within f(Q) gravity where electrical fields and dark matter are studied and provide novel mass–radius relations with models falling in the mass gap of the events GW190814 and GW200210. After formulating the basic equations and finding their relevant solutions, we impose the boundary conditions on the system under treatment. The decoupled solution for the strange stellar model with the dark matter density profile is obtained. The distribution patterns of the effective energy density and the radial as well as the tangential pressure and anisotropy in the system are intensively examined. The stability properties of the stellar configuration and the influence of dark matter are studied. The recent observations of supermassive compact star candidates such as PSR J1614–2230 and PSR J0952–0607 with observed masses greater than or equal to 2 M ⊙ have been employed in our study. Interestingly, the present study predicts the constraints on mass–radius measurements of the observed stars satisfying the equation of state based on the MIT bag model and employing the condition of mimicking, i.e., ρ θ = χ1ρPI in f(Q) gravity. Our graphical results exhibit that for a particular M–R curve with fixed values of the parameters, neutron stars having mass less than M max exist with larger radii within the context of the f(Q) formalism.

In this article, we apply the Finsler spacetime to develop the Einstein field equations in the extension of modified geometry. Following Finsler geometry, which is focused on the tangent bundle with a scalar function, a scalar equation should be the field equation that defines this structure. This spacetime maintains the required causality properties on the generalized Lorentzian metric manifold. The matter field is coupled with the Finsler geometry to produce the complete action. The developed Einstein field equations are employed on the strange stellar system to improve the study. The interior of the system is composed of a strange quark matter, maintained by the MIT bag equation of state. In addition, the modified Tolman–Oppenheimer–Volkov (TOV) equation is formulated. In particular, the anisotropic stress attains the maximum at the surface. The mass-central density variation confirms the stability of the system.