Mass-radius Ratio Research Articles

Exploring Gauss Bonnet gravity in the realm of Tolman–Kuchowicz spacetime

This study reveals the implication of charge within the framework of [Formula: see text] gravity models by considering the Tolman–Kuchowicz space–time. The use of the Bardeen model to describe the fundamental characteristics of the external geometry is an important aspect of current findings. Moreover, for the qualitative analysis, we compare all the parameters involved in the selected metric potentials with Bardeen’s model. We apply this analysis to the stars [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]. We study all the necessary characteristics of stellar structures, such as energy density and pressure progression, equation of state parameters, equilibrium conditions, mass–radius ratio, adiabatic index, and energy conditions. A thorough graphical analysis is provided to establish the viability of the considered [Formula: see text] models. It is important to emphasize that our acquired solutions are physically acceptable.

Charged anisotropic fluid sphere in [formula omitted] gravity satisfying Vaidya - Tikekar metric

In this paper, we study the properties of electrically charged anisotropic and spherically symmetric compact stars in f(Q) gravity theory. The field equations have been solved using the MIT-Bag Equation of State (EoS) along with the Vaidya–Tikekar potential. However, the specific form of charge E2(r)=q0L2r2(1+Lr2)2 has been used to study the charged compact star model. The interior charge anisotropic solution has been matched with the charged Schwarzchild-(Anti)-de-Sitter metric. In particular, this study has been conducted on different compact stars viz, EXO 1785-248, PSR J1614-2230, PSR J0740+620 and SMC X-1. The mass–radius ratio of these compact stars has been predicted, and the physical viability of the model has been checked through the behaviour of causality condition, matter variables, energy constraints, modified TOV equation, and adiabatic index of the star. In conclusion, we observe a well-behaved model of a compact star in f(Q) gravity with charged matter distribution.

Physical Parameters of 11,100 Short-period ASAS-SN Eclipsing Contact Binaries

Abstract Starting from more than 11,200 short-period (less than 0.5 days) EW-type eclipsing binary candidates with the All-Sky Automated Survey for Supernovae V-band light curves, we use the Markov Chain Monte Carlo algorithm and neural networks to obtain the mass ratio (q), orbital inclination (incl), fill-out factor (f), and temperature ratio (T s /T p ). After crossmatching with the Gaia DR3 database, the final sample contains parameters of 2399 A-type and 8712 W-type contact binaries (CBs). We present the distributions of parameters of these 11,111 short-period CBs. The mass ratio (q) and fill-out factor (f) are found to obey log-normal distributions, and the remaining parameters obey normal distributions. There is a significant period–temperature correlation of these CBs. Additionally, the temperature ratio (T s /T p ) tends to increase as the orbital period decreases for W-type CBs. There is no significant correlation between them for A-type CBs. The mass ratio and fill-out factor (q−f) diagram suggest there is no significant correlation between these two parameters. A clear correlation exists between the mass ratio and radius ratio. The radius ratio increases with the mass ratio. Moreover, the deep fill-out CBs tend to fall on the upper boundary of the q−R s /R p distribution, while the shallow fill-out CBs fall on the lower boundary.

Relativistic anisotropic solution satisfying vanishing complexity condition

In this paper, we investigated anisotropic solution for a self-bound compact star model. The solution is obtained via Vaidya–Tikekar metric function [Formula: see text] and the vanishing complexity factor condition. The physical analysis of the solution has been discussed in detail which includes mass-radius ratio, and stability analysis via adiabatic index for a secondary component of the GW190814 event for different values [Formula: see text]. Furthermore, we predicted the radii and obtained the compactness factor of different self-bound compact objects for different [Formula: see text]. Moreover, the hydrostatic equilibrium condition of the solution is also checked. The physical result shows that the solution so obtained is well behaved and may be useful for modeling the self-bound compact objects as far as observational data is concerned.

Complexity-free Vaidya-Tikekar model describing self-bound compact objects by gravitational decoupling

In this article, using gravitational decoupling under vanishing complexity condition, an anisotropic solution to spherically symmetric compact stars has been investigated. After obtaining the solution, a detailed physical analysis including thermodynamic parameters, mass-radius ratio, and stability analysis of the model corresponding to the secondary component of the GW190814 event has been done. To test the effect of gravitational decoupling on the mass-radius ratio, we fixed the mass of the secondary component of the GW190814 event corresponding to the pure general relativity scenario. Alongside this, we also predicted the radii and mass-radius ratio of 11 different compact stars using observational data of their masses for different values of β. Furthermore, the hydrostatic balance has been analyzed using the modified Tolman-Oppenheimer-Volkoff (TOV) equation. The physical analysis shows that our results are in good agreement as far as observational data is concerned.

Accurate mass–radius ratios for Hyades white dwarfs

ABSTRACT We use the ESPRESSO spectrograph at the Very Large Telescope to measure velocity shifts and gravitational redshifts of eight bona fide Hyades white dwarfs, with an accuracy better than 1.5 per cent. By comparing the gravitational redshift measurements of the mass-to-radius ratio with the same ratios derived by fitting the Gaia photometry with theoretical models, we find an agreement to better than one per cent. It is possible to reproduce the observed white dwarf cooling sequence and the trend of the mass-to-radius ratios as a function of colour using isochrones with ages between 725 and 800 Myr, tuned for the Hyades. One star, EGGR 29, consistently stands out in all diagrams, indicating that it is possibly the remnant of a blue straggler. We also computed mass-to-radius ratios from published gravities and masses, determined from spectroscopy. The comparison between photometric and spectroscopic stellar parameters reveals that spectroscopic effective temperature and gravity are systematically larger than the photometric values. Spectroscopic mass-to-radius ratios disagree with those measured from gravitational redshift, indicating the presence of systematics affecting the white dwarf parameters derived from the spectroscopic analysis.

Self-bound embedding Class I anisotropic stars by gravitational decoupling within vanishing complexity factor formalism

We present a spherically symmetric embedding Class I solution for compact star models using the gravitational decoupling approach. We have chosen a null complexity factor condition proposed by Herrera (Phys Rev D 97:044010, 2018) in the context of a self-gravitating system and derive the anisotropic solution through a systematic approach given by Contreras and Stuchlik (Eur Phys J C 82:706, 2022). In this regard, we use the Finch–Skea model along with the mimicking of mass constraint to find fluid pressure and the matter-energy density from the Einstein Field Equations (EFE). We tested the physical viability and impact of gravitational decoupling on the anisotropic solution through the graphical representation. Moreover, the energy exchange between the fluid distributions along with the mass-radius ratio of different compact objects has been also discussed.

Relativistic force-free models of the thermal X-ray emission in millisecond pulsars observed by NICER

ABSTRACTJPSeveral important properties of rotation-powered millisecond pulsars (MSPs), such as their mass-radius ratio, equation of state and magnetic field topology, can be inferred from precise observations and modelling of their X-ray light curves. In the present study, we model the thermal X-ray signals originated in MSPs, all the way from numerically solving the surrounding magnetospheres up to the ray tracing of the emitted photons and the final computation of their light curves and spectra. The magnetosphere is solved by performing general relativistic force-free simulations of a rotating neutron star (NS) endowed with a simple centred dipolar magnetic field, for many different stellar compactness and pulsar misalignments. From these solutions, we derive an emissivity map over the surface of the star, based on the electric currents in the magnetosphere. In particular, the emission regions (ERs) are determined in this model by spacelike four-currents that reach the NS. We show that this assumption, together with the inclusion of the gravitational curvature on the force-free simulations, lead to non-standard ERs facing the closed-zone of the pulsar, in addition to other ERs within the polar caps. The combined X-ray signals from these two kinds of ERs (both antipodal) allow to approximate the non-trivial interpulses found in several MSPs light curves. Our modelled X-ray signals are compared against very accurate NICER observations of four target pulsars: PSR J043-4715, PSR J1231-1411, PSR J2124-3358, and PSR J0030 + 0451; achieving very good simultaneous fits for their light curves and spectral distributions.

Effect of nucleon coupling constants on the mass radius ratio of proto neutron star PSR J0737-3039A

The effect of the nucleon coupling constants on the mass radius ratio (further, the surface gravitational redshift) of proto neutron star (PNS) PSR J0737-3039A is examined with relativistic mean field theory in consideration of a baryon octet. Here, five sets of nucleon coupling constants DD-MEI, GL85, GL97, GM1 and NL2 are used. The PNS’s temperature is assumed to be [Formula: see text] MeV and the mass the PNS PSR J0737-3039A is chosen as [Formula: see text]. The radius and the mass radius ratio of the PNS PSR J0737-3039A calculated by the five groups of nucleon coupling constants above are [Formula: see text] km and [Formula: see text]/km, respectively. The surface gravitational redshift [Formula: see text] of the PNS PSR J0737-3039A calculated from the above five groups of nucleon coupling constants is [Formula: see text].

Vaidya-Tikekar type anisotropic fluid model by gravitational decoupling

In this paper, a new interior solution for compact objects has been obtained using the minimal geometric deformation (MGD) approach along with the embedding Class I condition. Using MGD, the original system gets split into two parts, one of them is called the Einstein system and another one is the quasi-Einstein system for the extra source The Einstein system is solved by using the Vaidya-Tikekar metric along with the Class I condition, while for the quasi-Einstein system, the mimic approach for density constraint has been used such that A detailed physical analysis has been done as well as the physical viability of the model in terms of the thermodynamical variables, and different stability factors are also tested. Furthermore, the mass-radius ratio is also calculated for 12 different stars for different values of the decoupling constant which determines how the gravitational decoupling influences the compactness.

Spherically symmetric anisotropic charged solution under complete geometric deformation approach

We present a new systematic approach to find the exact gravitationally decoupled anisotropic spherical solution in the presence of electric charge by using the complete geometric deformation (CGD) methodology. To do this, we apply the transformations over both gravitational potentials by introducing two unknown deformation functions. This new systematic approach allows us to obtain the exact solution of the field equations without imposing any particular ansatz for the deformation functions. Specifically, a well-known mimic approach and equation of state (EOS) have been applied together for solving the system of equations, which determine the radial and temporal deformation functions, respectively. The matching conditions at the boundary of the stellar objects with the exterior Reissner–Nordström metric are discussed in detail. In order to see the physical validity of the solution, we used well-behaved interior seed spacetime geometry and solved the system of equations using the above approaches. Next, we presented several physical properties of the solution through their graphical representations. The stability and dynamical equilibrium of the solution have been also discussed. Finally, we predicted the radii and mass-radius ratio for several compact objects for different decoupling parameters together with the impact of the decoupling parameters on the thermodynamical observables.

Charged spherical solution in [formula omitted] gravity via embedding

The present article discusses a charged spherical solution in modified f(G,T) gravity under the embedding class I condition, where f(G,T)=G2+χT, where G is a Gauss–Bonnet term and T denotes a trace of energy momentum tensor, while χ is called coupling constant. The Exact solution of the Einstein–Maxwell’s field equations in f(G,T) gravity is obtained by taking a particular ansatz for radial component of the line element. The validity of the charged spherical solution has been tested via different physical analysis. The physical analysis shows that the present solution is well behaved. Moreover, we plotted the graphs for a particular star Vela X-1 for different χ, which show the trends of the thermodynamical observables like pressure, density, electric charge, energy conditions as well as impact of χ parameter on the above thermodynamical observables. On the other hand, we predicted the radii for 12 stars with different χ. The mass–radius ratio and surface red-shift are also calculated. Also, we have discussed the stability and equilibrium condition of the solution. Overall, the above analysis shows that obtained solution describes a physically viable and stable compact star. The prediction of radii from GW 170817 is also in agreement with our M−R curve.

Compact object with a local dark energy shell

We investigate some models of compact objects in the general relativity theory with cosmological constant [Formula: see text], based on two density profiles, one of them attributed to Stewart and the other one to Durgapal and Bannerji, proposed in the literature to model “neutron stars”. For them, a nonlocal equation of state with cosmological constant is obtained as a consequence of the chosen metric. In another direction, we obtain a solution for configurations with null radial pressure. The first model (based on Stewart’s density profile) turned out to be the most interesting, since surprisingly it admits the presence of dark energy in the interior of the star, in the outermost layers, for a certain range of mass–radius ratio [Formula: see text]. This dark energy is independent of the cosmological constant, since it is a consequence of the tangential pressure of the fluid be sufficiently negative. Still in this case, for other values of [Formula: see text], all the energy conditions are satisfied. Another advantage of this model, as well as that based on the density profile of Durgapal and Bannerji, is the existence of intervals of [Formula: see text] compatible with physically acceptable models for [Formula: see text], [Formula: see text] and [Formula: see text], which also allowed us to analyze the influence of [Formula: see text] on the behavior of the fluid with respect to the energy conditions. The other configuration studied here, [Formula: see text], only allows solutions for [Formula: see text], in order to ensure a positive mass for the object and to satisfy all the energy conditions in a specific range of [Formula: see text].

Modelling of dark energy stars with tolman IV gravitational potential

The present study explores the properties of dark energy star with high density under the dark energy equation of state (EOS) (pr=ωρ) with anisotropic fluid distribution, where ω describes the dark energy parameter. The relativistic dark-energy stellar structures are studied by adopting Tolman IV-type gravitational potential. In this relation we examine many physical properties through graphical plots and mathematical calculation, such as energy condition, compactness, mass-radius ratio, anisotropic nature and surface redshift. It is observed that the strong energy condition is violated whereas all other energy conditions are satisfied. We have also fitted radius corresponding to observed mass value for observed neutron stars, namely, PSRJ1416−2230,VelaX−1,4U1608−52,HerX−1 and PSRJ1903+327, which are compatible with the predicted values.

Charged anisotropic compact objects obeying Karmarkar condition

This research develops a well–established analytical solution of the Einstein-Maxwell field equations. We analyze the behavior of a spherically symmetric and static interior driven by a charged anisotropic matter distribution. The class I methodology is used to close the system of equations and a suitable relation between the anisotropy factor and the electric field is imposed. The inner geometry of this toy model is described using an ansatz for the radial metric potential corresponding to the well–known isotropic Buchdahl space-time. The main properties are explored in order to determine if the obtained model is appropriate to represent a real compact body such as neutron or quark star. We have fixed the mass and radii using the data of the compact objects SMC X–1 and LMC X–4. It was found that the electric field and electric charge have magnitudes of the order of ∼1021 [V/cm] and ∼1020 [C], respectively. The magnitude of the electric field and electric charge depends on the dimensionless parameter χ. To observe these effects on the total mass, mass–radius ratio and surface gravitational red–shift, we computed numerical data for different values of χ.

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.

Analytic radiation model for perfect fluid under homotopy perturbation method

An expression for mass of a spherically symmetric system is obtained by solving the Tolman–Oppenheimer–Volkoff equation, employing the homotopy perturbation method. With the help of this expression and the Einstein field equations, a set of interior solutions is arrived at. Thereafter, different aspects of the solution are explained as regards mass, density, pressure, energy, stability, mass–radius ratio, compactness factor and surface redshift. This analysis shows that all the physical properties, in connection to brown dwarf stars, are valid with the observed features.

Charged perfect fluid stellar structures with Bardeen model

This paper is devoted to study static spherically symmetric model in the presence of charged perfect fluid. This is the generalization of neutral perfect fluid (when there is no charge) through the solution of Einstein Maxwell equations. For this purpose, we consider a suitable form of gravitational potential [Formula: see text] and the electric field [Formula: see text], already used in the literature. The value of mass-radius ratio or compactness [Formula: see text], which depends upon the chosen model exceeds the value [Formula: see text] corresponding to neutral stars. The most important feature of the current study is to use the Bardeen model geometry instead of usual Reissner–Nordström model for the matching conditions. In this case the energy density and pressure remain positive, bounded and monotonically decreasing whereas electric field is monotonically increasing. Also the causality condition, i.e. the magnitude of speed of sound must be less than the speed of light, is satisfied. Moreover, the behavior of all the physical parameters at the center and on surface of star of mass [Formula: see text] and for Her X-1 are tabulated. All the results by graphical analysis and tabular information suggest that Bardeen model provides physically realistic stellar structures.

Charged anisotropic compact stars in Logarithmic-Corrected R2 gravity

We consider [Formula: see text] corrected model, i.e. [Formula: see text], where [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are arbitrary constant values, to investigate some of the interior configurations of static anisotropic spherical charged stellar structures. The existence of electric charge and a strong electric field confirms due to the higher values of pressure distribution and energy density of the matter inside the stars. Furthermore, for compact star configurations, we also consider the simplified MIT bag model equation of state (EoS) given by [Formula: see text], where [Formula: see text] is radial pressure, [Formula: see text] is energy density and [Formula: see text] is bag constant. This approach allows to find electric charge from the Einstein–Maxwell field equations. We have extensively discussed the behavior of the electric charge and anisotropic fluid distribution factor for five different values of [Formula: see text]. Interestingly, it is noticed during this study, for smaller values of [Formula: see text] we get intensity in electric charge. The Tolman–Oppenheimer–Volkoff equation (TOV), is modified in order to carry electric charge. In particular, we model the compact star candidates SAXJ 1808.4–3658 and Vela X-1 and give graphical representation of some important properties such as equilibrium condition, mass-radius ratio and surface redshift. In the end, our calculated solutions provide strong evidences for more realistic and viable charged stellar model.

Mass-radius ratio bound for horizonless charged compact object in higher dimensions

In this paper, the mass-radius ratio bound for horizonless compact object in higher dimensions is derived. Instead of considering the various matter conditions of the compact objects following Andreasson's approach, we focus on the conditions for the existence of dynamical compact objects. The radius of the outermost circular null geodesic is derived in higher dimensions, which is the lower bound on the minimally allowed radius of dynamically stable horizonless charged compact object. Subsequently, the upper bound on the mass-radius ratio is obtained. Our results are strongly dependent on the dimensions. What's more significant is that the developed bound is proven always to be stronger than the result following Andreasson's approach in higher dimensions.