Compact Stellar Objects Research Articles

Photoproduction of heavy QCD axions in supernovae

Compact stellar objects like supernovae and neutron stars are believed to cool by emitting axions predominantly via bremsstrahlung (NN→NNa), pion conversion (π−p+→Na), and photoproduction (γN→Na). In this paper, we study new contributions to the photoproduction channel pertaining to axions. We first point out the impact of anomaly-induced unavoidable Wess-Zumino-Witten term ∝εμναβFμν∂αaωβ in the photoproduction of such axions. We then perform a complementary data-driven study where the rate of photoproduction can be estimated from low-energy pion photoproduction data. We found that for such heavier axions, i.e., ma∼O(100) MeV, photoproduction processes can be dominant compared to the usual emission processes. In addition, the spectrum of these particles emitted in the process is significantly harder than those originating from bremsstrahlung. Published by the American Physical Society 2024

Anisotropic Durgapal-Fuloria compact stars in f(R) gravity

This study presented a new exact solution for anisotropic compact stellar objects within the framework of f(R)=R+αR2 gravity. In this context, the Durgapal-Fuloria metric potential has been employed to solve the field equation derived for f(R) theory. Furthermore, we have derived the generalized Darmois-Israel junction condition necessary for seamlessly connecting the interior region to the Schwarzschild exterior metric across the boundary hypersurface of the star in the context of f(R) gravity, and the interior solution is matched with the Schwarzschild exterior metric over the bounding surface of a compact star. These junction conditions stipulate that the pressure must not be zero at the boundary and should be proportional to the non-linear terms of f(R) gravity, a crucial aspect often overlooked by many researchers when investigating compact stellar models. Additionally, we derived the values of these parameters by using observational data of various compact stars (CSs), namely Her X-1, SAX J1808.4-3658, SMC X-1, LMC X-4, Cen X-3, 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, and PSR J1416-2230. This approach enables us to investigate the comprehensive analysis of solutions numerically and graphically. We conducted various physical tests, including gradient of energy density and pressures, anisotropy, stability, equilibrium conditions, energy-density constraints, mass function, compactness, redshift, and adiabatic index, to assess the feasibility of our models. Our findings demonstrate the consistent behavior of our models provides a satisfactory physical situation as far as the observational results are confirmed.

Extremely small stars in scalar-tensor gravity: When stellar radius is less than Schwarzschild one

We show analytically that there exist compact stellar objects akin to neutron stars whose radius is smaller than the Schwarzschild radius defined by Arnowitt-Deser-Misner (ADM) mass. The radius of the compact object is defined by the radius where the energy density and the pressure of ordinary matter vanish, while clouds of scalar(s) can extend beyond this radius – a situation that is often encountered in modified gravity theories, like F(R) gravity and the scalar–Einstein–Gauss-Bonnet gravity. The clouds of scalar mode(s) give additional contributions to the ADM mass and as a result, the corresponding Schwarzschild radius given by the ADM mass can be larger than that of the compact object.

Anisotropic stellar structures in energy–momentum squared theory with Tolman–Kuchowicz spacetime

This paper examines the viable characteristics of anisotropic compact stars in [Formula: see text] theory ([Formula: see text] is the Ricci scalar and [Formula: see text]). In this perspective, we use Tolman–Kuchowicz solutions [Formula: see text] and [Formula: see text] to examine the configurations of static spherically symmetric structures. The unknown constants are found by the first fundamental form of Darmois junction conditions. We analyze the behavior of fluid parameters in the interior of 4U 1538-52, PSRJ 1614-220, EXO 1785-248 and SAXJ 1808.4-3658 compact stars correspond to different models of this theory. Furthermore, the stability of the proposed compact stellar objects is examined through sound speed and adiabatic index methods. The satisfaction of requisite conditions ensures that stable compact objects exist in this framework.

Impact of Tolman–Kuchowicz potentials on Gauss–Bonnet gravity and isotropic stellar structures

In this manuscript, we study the behavior of charged isotropic compact stellar objects within the framework of modified f(G) theory of gravity by considering the Tolman–Kuchowicz spacetime. We use some matching condition of spherically symmetric space–time with Bardeen’s model as an exterior geometry and examine the physical behavior of stellar structures. In the current analysis, we discuss the energy conditions to check the viability of our model. Many physical aspects have been examined, such as energy density, pressure evolution, equation of state parameter, and causality condition. Furthermore, an equilibrium condition can be visualized through the modified Tolman–Oppenheimer–Volkov equation. Further, we study mass–radius function, compactness and redshift function, which are some essential features of charged compact star model. It is worthwhile to mention here for the current study that our stellar structure in the background of Bardeen’s model is more viable and stable.

Short-period pulsating hot subdwarf stars observed by TESS

We present the results of an extension of our Transiting Exoplanet Survey Satellite (TESS) search for short-period pulsations in compact stellar objects observed during the second and fourth years of the TESS mission, which targeted the northern ecliptic hemisphere. For many of the targets, we exploited unpublished spectroscopic data to confirm or re-evaluate the object’s spectral classification. From the TESS photometry, we identified 50 short-period hot-subdwarf pulsators, including 35 sdB and 15 sdOB stars. The sample contains 26 pulsators that were unknown prior to the TESS mission. Nine stars show signals at both low and high frequencies and have been categorized as “hybrid” pulsators. For each pulsator, we report the list of prewhitened frequencies, along with and their amplitude spectra calculated from the TESS data. We attempt to identify possible multiplets caused by stellar rotation and we report five candidates with rotation periods between 11 and 46 d. With the search for p-mode pulsating hot subdwarfs in TESS Sectors 1–60 complete, we discuss the completeness of the study, as well as the instability strip and the evolutionary status of the stars we found. We also compare the distribution of pulsation periods as a function of effective temperature and surface gravity with theoretical predictions. We find that the percentage of undetected pulsators in the TESS mission increases with decreasing brightness measurements of stars, reaching 25% near the 15th magnitude. When comparing the distribution of hot subdwarfs in the log g − Teff plane with stellar models, we underline the importance of a proper treatment of the hydrogen-rich envelope composition (strongly affected by microscopic diffusion processes). We also emphasize that the stellar mass is a significant factor in understanding the instability strip. The p-mode instability strip is confirmed to be narrower than predicted by prior non-adiabatic calculations based on models incorporating equilibrium between gravitational settling and radiative levitation for iron. This implies that competing mixing processes ignored in these models must play a role in reducing the amount of levitating iron in the stellar envelope. Interestingly, we find that the coolest p-mode pulsators with Teff ≲ 30 000 K (including the hybrid ones) tend to cluster around the terminal age of the extreme horizontal branch of canonical mass (TAEHB at ∼0.47 M⊙). This trend is expected from the non-adiabatic pulsation calculations. Otherwise, the overall pulsation period distributions tend to reproduce the predicted trends in Teff and log g.

Distinguishability of binary extreme-mass-ratio inspirals in low frequency band

The inspiral of compact stellar objects into massive black holes are one of the main astrophysical sources for the Laser Interferometer Space Antenna (LISA) and Taiji. These extreme-mass-ratio inspirals (EMRIs) have great potential for cosmology and fundamental physics. A binary extreme-mass-ratio inspiral (b-EMRI) describes the case where binary black holes (BBHs) are captured by a supermassive black hole. The b-EMRIs serve as multi-band gravitational wave sources and provide insights into the dynamics of nuclei and tests of general relativity. However, if the b-EMRIs can be distinguished from the normal EMRIs or not is still not clear. In this work, with a few of assumptions, and using the Teukolsky equation, we calculate the approximate gravitational waves of b-EMRIs and assess their detectability by space-based detectors. We also decouple the secondary object information from the Teukolsky equation, enabling us to calculate the energy fluxes and generate the waveforms more conveniently. Variations in the quadrupole of the binary result in small but non-negligible changes in energy fluxes and waveforms, making it possible to distinguish b-EMRI signals with data analysis. This opens up the potential of using b-EMRIs to test gravity theories and for further astrophysical studies.

Physical properties and maximum allowable mass-radius relation of complexity-free compact stellar objects within modified gravity formalism* *The authors MKJ and SKM acknowledge that this work is carried out under TRC Project (BFP/RGP/CBS/22/014). This study is also supported via funding from Prince Sattam bin Abdulaziz University project number (PSAU/2024/R/1445). The authors are thankful to the Deanship of Graduate Studies and Scientific

This paper investigates the physical properties and predicted radii of compact stars generated by the Tolman-IV complexity-free model within the background of modified gravity theory, particularly the -gravity theory, under complexity formalism for a spherically symmetric spacetime proposed by L. Herrera [Phys Rev D 97: 044010, 2018]. By solving the resulting set of differential equations, we obtain the explicit forms of the energy-momentum (EM) tensor components, including the density, radial pressure, and tangential pressure. The influence of the parameter χ on various physical properties of the star is thoroughly investigated. The model undergoes a series of rigorous tests to determine its physical relevance. The findings indicate that the model exhibits regularity, stability, and a surface with vanishing pressure. The boundary of this surface is determined by carefully selecting the parameter space. The complexity method employed in gravity offers an interesting approach for developing astrophysical models that are consistent with observable events as demonstrated by recent experiments. In this regard, we use observational data from the GW190814 event, detected by the LIGO and Virgo observatories, to investigate the validity of the Tolman-IV model in gravity. The analysis includes comparing the model's predictions with the observed characteristics of the compact object involved in the merger. In addition, data from two-millisecond pulsars, PSR J1614-2230 and PSR J0952-0607, are incorporated to further constrain the theoretical theories. However, we present a diagram depicting the relationship between the total mass and radius of the compact object candidates for different values of χ.

Gravitational waves with dark matter minispikes: Fourier-domain waveforms of eccentric intermediate-mass-ratio-inspirals

Abstract An intermediate mass black hole (IMBH) may have a dark matter (DM) minihalo around it and develop a spiky structure called DM minispike. Gravitational waves (GWs) can be produced if a stellar compact object, such as a black hole (BH) or neutron star, inspirals into the IMBH. This kind of systems are known as itermediate-mass-ratio-inspirals (IMRIs) and may be observed by space-based gravitational wave detectors including LISA, Taiji and Tianqin. In this paper, we lay the foundations for the construction of analytic expressions for Fourier-domain gravitational waves produced by eccentric IMRIs with DM minispikes in a post-circular or small-eccentricity approximation (e < 0.4). We take the effect of dynamical friction from the DM as a perturbation, and decompose the dynamical equations into perturbed part and unperturbed part. The equations are solved in a series expansion form about zero initial eccentricity to eighth order. The time-dependent, “plus” and “cross” polarizations are expanded in Bessel functions, which are then self-consistently reexpanded in a power series about zero initial eccentricity. The stationary-phase approximation is then employed to obtain the explicit DM-modified analytic expressions for the Fourier transform of the post-circular expanded, time-domain signal. We exemplify this framework by considering a typical IMRI with a DM minispike and find the GW detectability strongly depends on the radial profile of the DM distribution. When the density of DM is large enough, the signal to noise ratio (SNR) will be degraded significantly and a detection loss may occur if we use a template without the effect of DM to treat a signal including the DM effect. With the Fourier-domain gravitational waveforms we also estimate the accuracy of the measurement of the DM minispike parameters in our reference model. Our framework hold the promise to construct a “ready-to-use” Fourier-domain waveforms for data analysis of eccentric IMRIs with DM minispikes.

Impact of energy-momentum squared gravity on the geometry of stellar objects

This paper investigates the impact of energy–momentum squared gravity on the geometry of anisotropic compact stellar objects. In this perspective, we use the Tolman IV solution to examine the configuration of static spherically symmetric structures. The values of unknown constants are found by the first fundamental form of Darmois junction conditions. We consider four different models of this theory to analyze the behavior of physical quantities such as effective fluid parameters, anisotropy, energy constraints and equation of state parameters in the interior of considered compact stars. Sound speed and adiabatic index methods are used to determine the stability of proposed compact stars. It is found that the proposed compact stars are viable and stable in energy–momentum squared gravity.

Viable and Stable Compact Stellar Structures in f(Q,T)$f(\mathcal {Q},\mathcal {T})$ Theory

AbstractThe main objective of this paper is to investigate the impact of gravity on the geometry of anisotropic compact stellar objects, where is non‐metricity and is the trace of the energy‐momentum tensor. In this perspective, the physically viable non‐singular solutions to examine the configuration of static spherically symmetric structures is used. A specific model of this theory to examine various physical quantities in the interior of the proposed compact stars (CSs) is considered. These quantities include fluid parameters, anisotropy, energy constraints, equation of state parameters, mass, compactness, and redshift. The Tolman–Oppenheimer–Volkoff equation is used to examine the equilibrium state of stellar models, while the stability of the proposed CSs is investigated through sound speed and adiabatic index methods. It is found that the proposed CSs are viable and stable in the context of this theory.

Anisotropic compact stellar objects with a slow rotation effect

A new class of exact solutions depicting anisotropic compact objects is presented in the current work. This spherically symmetric matter distribution assumes a specific form of anisotropy to obtain the exact solution for the field equations. The obtained interior solutions are smoothly matched with the Schwarzschild exterior metric over the bounding surface of a compact star and together with the condition that the radial pressure vanishes at the boundary, the form of the model parameters are attained. One of the interesting features of the obtained solutions is the codependency of the metric potentials. We have considered the pulsar 4U1608-52 with its current estimated data (mass =1.57-0.29+0.30M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$=1.57^{+0.30}_{-0.29} ~M\\odot $$\\end{document} and radius =9.8±1.8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$=9.8 \\pm 1.8$$\\end{document} km [Özel in Astrophys J 820(1):28, 2016]) to study the model graphically. Moreover, we have studied the physical features and some important stability conditions for the model. Tabular comparison with other known pulsars infers that the obtained model represents a compact star within a radius of 8–12 km. Finally, we have found the angular momentum that causes the dragging of inertial frames of the slowly rotating equilibrium compact objects.

The dragon-II simulations – III. Compact binary mergers in clusters with up to 1 million stars: mass, spin, eccentricity, merger rate, and pair instability supernovae rate

ABSTRACT Compact binary mergers forming in star clusters may exhibit distinctive features that can be used to identify them among observed gravitational-wave sources. Such features likely depend on the host cluster structure and the physics of massive star evolution. Here, we dissect the population of compact binary mergers in the dragon-II simulation data base, a suite of 19 direct N-body models representing dense star clusters with up to 106 stars and $\lt 33~{{\ \rm per\ cent}}$ of stars in primordial binaries. We find a substantial population of black hole binary (BBH) mergers, some of them involving an intermediate-mass BH (IMBH), and a handful mergers involving a stellar BH and either a neutron star (NS) or a white dwarf (WD). Primordial binary mergers, $\sim 30~{{\ \rm per\ cent}}$ of the whole population, dominate ejected mergers. Dynamical mergers, instead, dominate the population of in-cluster mergers and are systematically heavier than primordial ones. Around 20 per cent of dragon-II mergers are eccentric in the Laser Interferometer Space Antenna (LISA) band and 5 per cent in the LIGO band. We infer a mean cosmic merger rate of $\mathcal {R}\sim 30(4.4)(1.2)$ yr−1 Gpc−3 for BBHs, NS–BH, and WD–BH binary mergers, respectively, and discuss the prospects for multimessenger detection of WD–BH binaries with LISA. We model the rate of pair-instability supernovae (PISNe) in star clusters and find that surveys with a limiting magnitude mbol = 25 can detect ∼1–15 yr−1 PISNe. Comparing these estimates with future observations could help to pin down the impact of massive star evolution on the mass spectrum of compact stellar objects in star clusters.

Compact stellar model with vanishing complexity under Vaidya–Tikekar background geometry

We make use of the condition of vanishing complexity, based on the current definition proposed by Herrera (Phys Rev D 97:044010, 2018), to find exact interior solutions to the Einstein equations for describing compact stellar objects. In the framework of general relativity, the complexity factor is an outcome of the orthogonal splitting of the Riemann tensor from which structure scalars are obtained. By using the Vaidya–Tikekar (V–T) metric ansatz (J Astrophys Astron 3:325, 1982) for the spacetime of a static spherically symmetric matter distribution, we model superdense, relativistic stars. The interior spacetime is matched to the exterior Schwarzschild solution across the boundary of the star where the radial pressure vanishes. The physical viability of the model has been tested following the current data corresponding to the pulsar 4U1820-30\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ 4U 1820-30 $$\\end{document}. The stability of the model fulfilled the given criteria, namely the Tolman–Oppenheimer–Volkoff equation, the adiabatic index and the causality conditions.

Proton-cluster femtoscopy with the HADES experiment

The matter created in Ag+Ag collisions at √SNN = 2.55 GeV, as measured with the HADES experiment, can be characterized by similar thermodynamic quantities as Neutron Star Mergers, thus becoming an essential reference for the understanding of these compact stellar objects. One of the methods applied to investigate heavy-ion collisions are femtoscopic correlations. They are a unique tool for the determination of the interactions between hadrons and allow to search for possible exited or unbound states of nuclear matter. We performed precise experimental studies of the correlations between protons and different clusters and compared them with the existing theoretical descriptions.

A study of compact stars within Rastall gravity

In this paper, we construct the exact interior solutions for compact stellar objects for perfect fluid distribution in phantom region in the framework of a non-conserved theory, i.e. Rastall gravity (RG). Under these circumstances, we develop the Einstein field equations (EFEs) for spherically symmetric metric using general forms of metric potentials, [Formula: see text] and [Formula: see text], here [Formula: see text] and [Formula: see text]. By matching of interior and exterior regions of the metric, we obtain the values of unknown constants of our considering model which helps to sketch the nature of important physical quantities like density, pressure, energy conditions, and stability. Finally, our obtained results lead us to conclude that our solutions are well behaved and physically viable for the specific choices of model parameters for two different stars (Vela X-1 and 4U1820-30).

Study of anisotropic stellar structures in [formula omitted] theory

This manuscript examines how effective matter variables influence the geometry of compact stellar objects with anisotropic matter configuration in modified f(R,φ,χ) gravity, where R represents the Ricci scalar, φ is the scalar field and χ is a kinetic term depending on the scalar field. The unknown constants in the metric potentials are determined by the smooth matching of an interior region with the exterior spacetime. We then check the viability of some selected stars through various physical quantities, i.e., effective matter contents, anisotropy and energy constraints. We also examine the equilibrium and stable states through the Tolman–Oppenheimer–Volkoff equation and sound speed/adiabatic index, respectively. This comprehensive analysis ensures that viable and stable compact stars exist in this modified theory as all the necessary conditions are satisfied.

Physical analysis of anisotropic compact stars in f(𝒬) gravity

The main objective of this study is to investigate the stability and viability of anisotropic compact stellar objects using the Krori–Burua solutions in [Formula: see text] gravity, where [Formula: see text] is a nonmetricity scalar that explains the gravitational effects. We use a static spherical metric in the inner region and Schwarzschild spacetime in the outer region of the Her X-I, SAX J 1808.4-3658 and 4U1820-30 compact stars to investigate their physical properties. By using observed values of the radius and mass of the considered compact stars, the unknown parameters are determined. We use a particular model of this theory to examine the behavior of energy density, pressure components, anisotropy, equation of state parameters and energy constraints in the interior of the proposed stellar objects. The Tolman–Oppenheimer–Volkoff equation is used to analyze the equilibrium state of these stars and causality condition, Herrera cracking method, adiabatic index methods are used to determine their stability. It is found that revolutionary technique sheds new light on the development of observationally accurate gravity model.

The effect of modified hybrid and logarithmic teleparallel gravity on the interior solutions of compact stars

This study aims to investigate spherically symmetric anisotropic solutions that describe compact stellar objects in the modified Rastall teleparallel (MRT) theory of gravity. In order to achieve this goal, we utilize the Karmarkar condition to evaluate the spherically symmetric components of the line element. We explore the field equations by selecting appropriate off-diagonal tetrad fields for two different scenarios. In the first scenario, we use a hybrid form of f(T)=βemTTn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(T)=\\beta e^{m T} T^n$$\\end{document} and a linear equation of state (EoS) pr=ξρ+ϕ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p_r=\\xi \\rho +\\phi $$\\end{document}, where 0<ξ<1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0< \\xi < 1$$\\end{document}, to evaluate h(T). In the second scenario, we again use a hybrid form of f(T)=βemTTn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(T)=\\beta e^{m T} T^n$$\\end{document} and a logarithmic form of h(T)=ψlog(ϕTχ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$h(T)=\\psi \\log (\\phi T^{\\chi })$$\\end{document}. We aim to investigate the possible forms of gravity modifications by evaluating the function for different values of m and n, reducing the gravity forms to hybrid, power law form, and exponential form. Our findings reveal that the exponential-logarithmic case is unstable in our scenario. To the best of our knowledge, we are the first to attempt to explore compact star models in MRT gravity. After obtaining the field equations, we investigate different physical parameters that demonstrate the stability and physical acceptability of the stellar models. We utilize observational data, such as the mass and radius of the PSRJ1416-2230\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$PSRJ\\;1416-2230$$\\end{document} model, to ensure the physical plausibility of our findings.

Anisotropic compact stars admitting karmarkar condition in f(𝒬) theory

The major goal of this study is to examine the viability and stability of anisotropic compact stellar objects using the Karmarkar condition in [Formula: see text] gravity, where [Formula: see text] is a scalar of nonmetricity that explains gravitational effects. We consider a static spherical metric in inner and Schwarzschild spacetime in outer regions of the star to analyze the physical attribute of Vela [Formula: see text], SAX J 1808.4−3658, 4U 1608−52, PSR J0348+0432 and 4U 1820−30 compact stars. The unknown parameters are determined through observational values of the radius and mass of the considered compact stars. We take a specific model of this theory to evaluate the energy density, pressure elements, anisotropy, equation of state parameters and energy bounds in inner region of suggested stellar objects. The equilibrium position of these stars is examined through Tolman–Oppenheimer–Volkoff equation and their stability checked by Herrera cracking method and adiabatic index. We find more viable as well as stable compact stars in this modified theory.