Search

Gravitational instability in the outskirts of active galactic nuclei (AGN) disks leads to disk fragmentation and formation of ∼300 M ⊙ supermassive stars with potentially long lifetimes. Alternatively, stars can be captured ex situ and grow from gas accretion in the AGN disk. However, the number density distribution throughout the disk is limited by thermal feedback as their luminosities provide the dominant heating source. We derive equilibrium stellar surface density profiles under two limiting contexts: in the case where the stellar lifetimes are prolonged, due to the recycling of hydrogen-rich disk gas, only the fraction of gas converted into heat is removed from the disk accretion flow. Alternatively, if stellar composition recycling is inefficient and stars can evolve off the main sequence, the disk accretion rate is quenched toward smaller radii resembling a classical starburst disk, albeit the effective removal rate depends not only on the stellar lifetime, but also the mass of stellar remnants. For AGNs with central supermassive black hole masses of ∼106–108 M ⊙ accreting at ∼0.1 Eddington efficiency, we estimate a total number of 103–105 massive stars and the rate of stellar mergers to be 10−3 to 1 yr−1. We initiate the detailed study of the interaction between a swarm of massive stars through hydro and N -body simulations to provide better prescriptions of dynamical processes in AGN disks, and to constrain more accurate estimates of the stellar population. [ABSTRACT FROM AUTHOR]

In this paper, we study quintessence compact stars in the paradigm of pure Lovelock gravity. We derive the field equations using a spherically symmetric space–time. Specifically, we discuss the equivalence of Einstein's Lovelock gravity in four-dimensional space–time, Gauss–Bonnet term equivalent Lovelock gravity in seven-dimensional space–time and sixteen-dimensional Lovelock gravity by exploring the impact of the quintessence field parameter on features of compact stars in anisotropic matter fields. For matter inside the star, we use Tolman–Kuchowiz space–time. We discuss the density of the compact star and the density related to the quintessence matter field. We also explore the pressure profiles, anisotropy, speeds of sound for stability, EoS state parameters, mass-to-radius profile, compactification, gravitational and gradients for different values of N, which change the dimensions ( d = 3 N + 1 ) of pure Lovelock gravity. [ABSTRACT FROM AUTHOR]

A dark star cluster (DSC) is a system in which the cluster potential is dominated by stellar remnants, such as black holes and neutron stars having larger masses than the long-lived low-mass stars. Due to mass segregation, these remnants are located in the central region of the cluster and form a dark core. We expect that at a few kpc from the Galactic Centre, the efficient evaporation of the lower-mass stars caused by the strong tidal force exposes the dark core, because the dynamical properties of the DSC are dominated by the remnants. Due to the invisibility of the remnants, finding a DSC by observation is challenging. In this project, we use N -body simulations to obtain models of DSCs and try to discern observables that signify a DSC. We consider four observables: the mass spectrum, the observational mass density profile, the observational velocity dispersion profile and the mass segregation. The models show that a DSC typically exhibits two distinct characteristics: for a given mass in stars and a given half-light radius, the expected velocity dispersion is underestimated when only visible stars are considered, and there is a lack of measurable mass segregation among the stars. These properties can be helpful for finding DSCs in observational data, such as the Gaia catalogue. [ABSTRACT FROM AUTHOR]

We consider scenarios for non-thermal particle acceleration and re-acceleration in the central cores of compact massive star clusters, aided by insights from high-resolution hydrodynamic simulations. We show that (i) particles are unlikely to interact with many shocks during their lifetimes in the core; (ii) colliding flows do not produce hard spectra; and (iii) turbulent re-acceleration in the core is suppressed. Inefficient re-acceleration mechanisms are not expected to produce hard components nor to increase the maximum energy within the cores of massive star clusters. Models in which the observed ultra-high-energy gamma rays originate in the core of massive stellar clusters are thus disfavoured. [ABSTRACT FROM AUTHOR]

Over the last decade, evidence has accumulated that massive stars do not typically evolve in isolation but instead follow a tumultuous journey with a companion star on their way to core collapse. While Roche-lobe overflow appears instrumental for the production of a large fraction of Type Ib and Ic supernovae (SNe), variations in the initial orbital period, Pinit, of massive interacting binaries may also produce a wide diversity of case B, BC, or C systems, with pre-SN stars endowed from minute to massive H-rich envelopes. Focusing here on the explosion of the primary donor star, originally 12.6 M⊙, we used radiation hydrodynamics and nonlocal thermodynamic equilibrium time-dependent radiative transfer to document the gas and radiation properties of such SNe, covering Types Ib, IIb, II-L, and II-P. Variations in Pinit are the root cause of the wide diversity of our SN light curves, which present single-peak, double-peak, fast-declining, or plateau-like morphologies in the V band. The different ejecta structures, expansion rates, and relative abundances (e.g., H, He, and 56Ni) can lead to a great deal of diversity in terms of spectral line shapes (absorption versus emission strength and width) and evolution. We emphasize that Hα is a key tracer of these modulations, and that He I 7065 Å is an enduring optical diagnostic for the presence of He. Our grid of simulations fares well against representative Type Ib, IIb, and II-P SNe, but interaction with circumstellar material, which is ignored in this work, is likely at the origin of the tension between our Type II-L SN models and observations (e.g., of SN 2006Y). Remaining discrepancies in the rise time to bolometric maximum of our models call for a proper account of both small-scale and large-scale structures in core-collapse SN ejecta. Discrepant Type II-P SN models, with a high plateau brightness but small spectral line widths, can be fixed by adopting more compact red-supergiant star progenitors. [ABSTRACT FROM AUTHOR]

In the centers of dense star clusters, close encounters between stars and compact objects are likely to occur. We studied tidal disruption events of main-sequence (MS) stars by stellar-mass black holes (termed μTDEs), which can shed light on the processes occurring in these clusters, including being an avenue in the mass growth of stellar-mass BHs. Using the moving-mesh hydrodynamics code AREPO, we performed a suite of 58 hydrodynamics simulations of partial μTDEs of realistic, MESA-generated MS stars by varying the initial mass of the star (0.5 M⊙ and 1 M⊙), the age of the star (zero-age, middle-age and terminal-age), the mass of the black hole (10 M⊙ and 40 M⊙), and the impact parameter (yielding almost no mass loss to full disruption). We then examined the dependence of the masses, spins, and orbital parameters of the partially disrupted remnant on the initial encounter parameters. We find that the mass lost from a star decreases roughly exponentially with increasing approach distance and that a 1 M⊙ star loses less mass than a 0.5 M⊙ one. Moreover, a more evolved star is less susceptible to mass loss. Tidal torques at the closest approach spin up the remnant very close to break-up velocity when the impact parameter is low. The remnant star can be bound (eccentric) or unbound (hyperbolic) to the black hole; hyperbolic orbits occur when the star's central density concentration is relatively low and the black-hole-star mass ratio is high, which is the case for the disruption of a 0.5 M⊙ star. Finally, we provide best-fit analytical formulae for the aforementioned range of parameters that can be incorporated into cluster codes to model star-black-hole interaction more accurately. [ABSTRACT FROM AUTHOR]

In this paper, we obtain analytical solutions of Einstein field equations for a spherically symmetric anisotropic matter distributions. For this purpose physically meaningful metric potential corresponds to g rr and a particular choice of the anisotropy has been utilized to obtain the solutions in closed form. This class of solution has been used to characterized observed pulsars from different aspects. Smooth matching of interior spacetime metric with the exterior Schwarzschild metric and in addition with the condition of vanishing radial pressure across the boundary leads us to determine the model parameters. Pulsar 4 U 1820 - 30 with its current estimated data for mass and radius (Mass = 1.58 M ⊙ and radius = 9.1 km) has been allowed for testing the physical acceptability of our developed model. We have graphically analyzed the gross physical features of the observed pulsar. The stability of the model is also discussed under the conditions of causality, adiabatic index and generalized Tolman–Oppenheimer–Volkov (TOV) equation under the forces acting on the system. Few more pulsars with their have been considered, to show that this model is compatible with observational data, and all the requirements of a realistic star are highlighted. Mass-radius (M–R) relationship have been generated for our model. The impact of anisotropy on the gross physical features of stars have been explored with the graphical presentation. [ABSTRACT FROM AUTHOR]

This paper is devoted to observe the physical attributes of isotropic relativistic spherical objects in the context of Rastall theory of gravity. In order to inspect the structural composition of spherical objects, the Tolman IV solution is taken into account. The unknown parameters associated with Tolman IV solution are evaluated through matching conditions with derived values of radii and masses of some specific star models. The consistency of the adopted ansatz is analyzed via graphical interpretation of matter variables, equation of state parameter, mass components, energy constraints, causality condition and stellar equation for several choices of Rastall parameter. It is observed that the considered solution does not admit singularities in the matter variables. Moreover, in accordance with the graphical analysis, the stellar models satisfy all physical requirements anticipated in a realistic star. It is also shown that for vanishing Rastall coupling parameter, the standard outcomes of general relativity can be retrieved. [ABSTRACT FROM AUTHOR]

The massive stars end their lives by supernova explosions leaving central compact objects that may evolve into neutron stars. Initially, after birth, the star remains hot and gradually cools down. We explore the matter and star properties during this initial stage of the compact stars considering the possibility of the appearance of deconfined quark matter in the core of the star. At the initial stage after the supernova explosion, the occurrence of non-radial oscillation in the newly born compact object is highly possible. Non-radial oscillations are an important source of gravitational waves (GWs). There is a high chance for GWs from these oscillations, especially the nodeless fundamental (f) mode to be detected by next-generation GW detectors. We study the evolution in frequencies of non-radial oscillation after birth considering phase transition and predicting the possible signature for different possibilities of theoretical compact star models. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to obtain physically stable stellar models coupled with anisotropic matter distribution in the context of f (ℛ , T 2) theory. For this, we consider a static spherical geometry and formulate modified field equations containing various unknowns such as matter determinants and metric potentials. We then obtain a unique solution to these equations by employing Durgapal–Fuloria ansatz possessing a constant doublet. We also use matching criteria to calculate the values of these constants by considering the Schwarzschild exterior spacetime. Two different viable models of this modified theory are adopted to analyze the behavior of effective matter variables, anisotropy, energy conditions, compactness and redshift in the interiors of Her X-1, PSR J0348-0432, LMC X-4, SMC X-1, Cen X-3, and SAX J 1808.4-3658 star candidates. We also check the stability of these models by using three different physical tests. It is concluded that our considered stars satisfy all the physical requirements and are stable in this modified gravity for the considered parametric values. [ABSTRACT FROM AUTHOR]

We report here a new exact solution of the Einstein field equations that describes a static spherically symmetric, anisotropic compact stellar fluid sphere. A generalized metric form corresponding to the g rr component and a specific anisotropic profile generates the model. The new class of generalized solutions reduces to Finch-Skea, Vaidya Tikekar and Schwarzschild interior solutions for specific cho-ices of the model parameters. The model parameters have been determined from the continuity of the interior and exterior metrics at the surface of the star and setting the radial pressure at the boundary to zero. Recent observed measurements from some pulsars as sources have been utilized to validate our model. [ABSTRACT FROM AUTHOR]

Similar to Rastall gravity we introduce matter-geometry nonminimal coupling which is proportional to the gradient of quadratic curvature invariants. Those are mimicking the conformal trace anomaly when backreaction of the quantum fields to a curved spacetime geometry is considered. We consider a static spherically symmetric stellar structure with anisotropic fluid and Krori-Barua metric potentials model to examine the theory. Confronting the model with NICER + XMM-Newton observational constraints on the pulsar PSR J0740 + 6620 quantifies the amount of the nonminimal coupling via a dimensionless parameter ϵ ≃ - 0.01 . We verify that the conformal symmetry is broken everywhere inside the pulsar as the trace anomaly Δ > 0 , or equivalently the trace of the stress-energy tensor T < 0 , whereas the adiabatic sound speed does not violate the conjecture conformal upper limit v r 2 / c 2 = 1 / 3 . The maximum compactness accordingly is C max = 0.752 which is 4 % higher than GR. Notably, if the conformal sound speed constraint is hold, observational data excludes ϵ ≥ 0 up to ≥ 1.6 σ . The stellar model is consistent with the self-bound structure with soft linear equation of state. Investigating possible connection with MIT bag model of strange quarks sets physical bounds from microscopic physics which confirm the negative value of the parameter ϵ . We estimate a radius R = 13.21 ± 0.96 km of the most massive observed compact star PSR J0952−0607 with M = 2.35 ± 0.17 M ⊙ . Finally, we show that the corresponding mass-radius diagram fits well lowest-mass pulsar HESS J1731−347 and highest-mass pulsar PSR J0952−0607 ever observed as well as the intermediate mass range as obtained by NICER and LIGO/Virgo observations. [ABSTRACT FROM AUTHOR]

Compact stars have been perceived as natural laboratories of matter at an extremely high density. The uncertainties of the equation of state (EOS) of matter can be constrained by observing compact stars. In this review, we investigate the EOSs, global structure, and elastic properties of compact stars. We focus in detail on how to constrain the above properties of compact stars via asteroseismology. Observations that include studies of quasi-periodic oscillations from giant flares of soft gamma-ray repeaters and gravitational waves provide information about the elastic properties and internal compositions of compact stars. [ABSTRACT FROM AUTHOR]

In this paper, the possibility of existing a novel class of compact charged spheres based on a charged perfect fluid within the realm of f(Q)$f(Q)$ gravity theory is explored. The authors started by proposing physically meaningful explicit formulas for the potential, denoted λ(r)$\lambda (r)$, and the electric field to find a close‐form solution. More precisely, the change of the dependent variable approach by exploiting the transformation Y(r)=eζ(r)/2$Y(r)=e^{\zeta (r)/2}$ is applied. Successively, the field equations analytically are solved and generate the most general solution, which leads us to examine various significant aspects of the stellar system. These aspects comprise the regularity of gravitational potentials, energy density and pressure, electric charge, the mass‐radius relationship, subluminal sound velocities in the radial direction, and the adiabatic index for charged compact stars. For a more in‐depth system study, mass measurements using contour diagrams are carried out. This mainly involves varying the variable parameters β1$\beta _1$ and E0$E_0$ to distinguish their effect on the mass distribution within the stellar structure. What is more, the electric charge controls the stability of the stellar system is shown, which yields that a stable system can possess a maximum charge of order 1020C$10^{20}\nobreakspace \text{C}$. The results strongly argue that charged stars could conceivably exist in nature and that such a deviation from traditional theories may be seen in future astrophysical observations. In this paper, the possibility of existing a novel class of compact charged spheres based on a charged perfect fluid within the realm of f(Q)$f\!(\mathcal{Q})$ gravity theory is explored. The authors started by proposing physically meaningful explicit formulas for the potential, denoted λ$\lambda$(r), and the electric field to find a close‐form solution. More precisely, the change of the dependent variable approach by exploiting the transformation Y(r) = eζ(r)∕2 is applied. Successively, the field equations analytically are solved and generate the most general solution, which leads us to examine various significant aspects of the stellar system. These aspects comprise the regularity of gravitational potentials, energy density and pressure, electric charge, the mass‐radius relationship, subluminal sound velocities in the radial direction, and the adiabatic index for charged compact stars. For a more in‐depth system study, mass measurements using contour diagrams are carried out. This mainly involves varying the variable parameters β1 and E0 to distinguish their effect on the mass distribution within the stellar structure. What is more, the electric charge controls the stability of the stellar system is shown, which yields that a stable system can possess a maximum charge of order 1020 C. The results strongly argue that charged stars could conceivably exist in nature and that such a deviation from traditional theories may be seen in future astrophysical observations. [ABSTRACT FROM AUTHOR]

This work mainly focuses on modeling the charged compact stars and investigating their properties in the framework of f (T) modified gravity, under the accelerated phase of the universe. In this study, we have introduced the modified gravity and dark matter to culture the evolution of the charged neutron stars by considering the present situation. True knowledge and proper study on the macroscopic parameters of the compact stars are very much needed to realize the microscopic properties and behavior of the core nuclear matter at very high density and pressure. The existence of modified Chaplygin gas as an exotic fluid inside the core of these stars in f (T) gravity plays a very important role inside the stars. We have found out that exotic fluid has a great impact on the equation of state of the core nuclear matter and even on the stability of the compact stars. Pressure anisotropy reduces the tidal deformability of the charged stars in an appreciable amount and helps to get a more compact structure. But surprisingly, the compact stars are still able to maintain their spherically stable and equilibrium configuration. Further, we can put constraints on several macroscopic parameters of the compact stars and can investigate their evolution from our present investigation. [ABSTRACT FROM AUTHOR]

We conducted a study to investigate the relationship between X-ray binaries (XRBs) and compact star clusters in the nearby star-forming galaxies NGC 4490 and NGC 4214. By analysing archival data from Chandra , we identified a total of 32 XRBs with X-ray luminosities Lx > 1036 erg s−1 in both galaxies. Utilizing data from HST /WFC3/UVIS, we presented a new catalogue of 715 compact star clusters in NGC 4490 and identified 312 such clusters in NGC 4214. In the case of NGC 4490, 14 of the 17 XRBs are associated with clusters, whereas in NGC 4214 all 15 XRBs are connected to clusters within a radius of <200 pc. Furthermore, among the XRBs in NGC 4490, 12 out of the 17 have optical counterparts. Similarly, in NGC4214, 11 out of the 15 XRBs exhibit optical counterparts. We have evidence for a substantial population of high-mass X-ray binaries (HMXBs) associated with clusters, accounting for ∼70  per cent and 40  per cent of the detected XRBs in NGC 4490 and NGC 4214, respectively. HMXBs are often found near young, less massive clusters, while low-mass X-ray binaries (LMXBs) are associated with older, more massive clusters in these galaxies. Intermediate-mass XRBs in NGC 4214, on the other hand, tend to be close to young clusters, suggesting that their formation mechanism is more similar to HMXBs than to LMXBs. [ABSTRACT FROM AUTHOR]

This paper explores the viability and stability of compact stellar objects characterized by anisotropic matter in the framework of f (Q , T) theory, where Q denotes non-metricity and T represents the trace of the energy-momentum tensor. We consider a specific model of this theory to obtain explicit expressions for the field equations governing the behavior of matter and geometry in this context. Furthermore, the Karmarkar condition is employed to assess the configuration of static spherically symmetric structures. The values of unknown constants in the metric potentials are determined through matching conditions of the interior and exterior spacetimes. Various physical quantities such as fluid parameters, energy constraints, equation of state parameters, mass, compactness and redshift are graphically analyzed to evaluate the viability of the considered compact stars. The Tolman–Oppenheimer–Volkoff equation is used to examine the equilibrium state of the stellar models. Moreover, the stability of the proposed compact stars is investigated through sound speed and adiabatic index methods. This study concludes that the proposed compact stars analyzed in this theoretical framework are viable and stable, as all the required conditions are satisfied. [ABSTRACT FROM AUTHOR]

We study the higher dimensional scenario of an anisotropic compact star using the Buchdahl–Vaidya–Tikekar metric ansatz. In our formalism, the anisotropy is assumed in such a way that, in the absence of it, the solution reduces to Schwarzschild's interior solution in D ≥ 4 dimensions. The model is so developed that it correlates anisotropy to the curvature parameter K which characterizes a departure from spherical geometry of the t = constant hypersurface of the associated spacetime when embedded in a 4 dimensional Euclidean space. Due to the particular choice of anisotropy, the pressure balancing equation for hydrostatic equilibrium continues to have the same form in higher dimensions. Consequently, our approach permits extending a four-dimensional solution to a higher dimensional spacetime without deforming the sphericity of the configuration. Making use of the model, we propose a higher dimensional anisotropic analogue of the Buchdahl bound on compactness. We show that additional dimension as well as anisotropy reduce the compactification limit. Our technique helps to regain the original Buchdahl limit in D = 4 dimensions and also, in the absence of anisotropy, the compactification limit in higher dimensions obtained earlier by Leon and Cruz (Gen Relativ Gravit 32:1207–1216, 2000. https://doi.org/10.1023/A:1001982402392). It turns out that the maximum achievable dimension remains model dependent through the causality condition and the compactification limit. We scrutinize the model under all the requisite physical conditions for a relativistic anisotropic fluid sphere which might serve as the internal structure of a compact star in higher dimensions. We analyze the consequences of the departure from homogeneous spherical distribution and dimensionality on the physical behaviour of the star. The EOS becomes stiffer in higher dimensions and comparatively lower anisotropic stress. Our calculation shows that the central density reduces as we move towards higher dimensions and inclusion of anisotropy increases the rate of fall of the density profile. We also note that the two pressures get reduced considerably in higher dimensions. We show that, for a given curvature parameter specifying the sphericity, an extra dimension is analogous to moving towards a homogeneous distribution of an anisotropic star. [ABSTRACT FROM AUTHOR]

Within the context of Rastall gravity, we investigate the hydrostatic equilibrium and dynamical stability against radial pulsations of compact stars, where a free parameter β measures the deviations from General Relativity (GR). We derive both the modified Tolman–Oppenheimer–Volkoff (TOV) equations and the Sturm–Liouville differential equation governing the adiabatic radial oscillations. Such equations are solved numerically in order to obtain the compact-star properties for two realistic equations of state (EoSs). For hadronic matter, the fundamental mode frequency ω 0 becomes unstable almost at the critical central energy density corresponding to the maximum gravitational mass. However, for quark matter, where larger values of | β | are required to observe appreciable changes in the mass-radius diagram, there exist stable stars after the maximum-mass configuration for negative values of β . Using an independent analysis, our results reveal that the emergence of a cusp can be used as a criterion to indicate the onset of instability when the binding energy is plotted as a function of the proper mass. Specifically, we find that the central-density value where the binding energy is a minimum corresponds precisely to ω 0 2 = 0 . [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to examine singularity-free solutions within the framework of anisotropic solutions for the Chaplygin equation of state in f (R , ϕ , X) modified gravity theory. Herein, R signifies the Ricci scalar, ϕ denotes the scalar field, and X represents the kinetic term associated with ϕ. The investigation employs the Krori–Barua metric to explore the characteristics of an anisotropic compact star. In the course of our analysis, we specifically consider observational data about three distinct stellar structures: Her X-I, LMC X-4, and 4U 1538-52. Our inquiry extends to the graphical examination of various physical parameters, encompassing energy density, pressure components, anisotropic components, equation of state parameters, equilibrium conditions, stability analysis, adiabatic index, and energy conditions. Furthermore, we delve into the intricacies of the mass-radius function, compactness factor, and surface redshift–integral features of charged compact stars. The culmination of our findings suggests that the f (R , ϕ , X) theory of gravity when subjected to observational scrutiny, manifests as realistic, stable, and devoid of singularities. [ABSTRACT FROM AUTHOR]

The construction of compact star models with quintessence and cloud of strings anisotropic fluid lays the foundation for the research presented in this paper, which focuses on the ansatz of f(Q) gravity. We utilized a spherically symmetric spacetime to derive the field equations incorporating quintessence and cloud of strings anisotropic matter fields. The well-known Karmarkar condition was employed to obtain the gravitational components of the spherically symmetric spacetime. The constant parameters used in the study were obtained by applying junction conditions on the interior and exterior spacetimes. We used the mass and radius of P S R J 1 6 1 4 − 2 2 3 0 & S M C X − 1 , which are already present in the literature. Afterward, we calculated the important properties of quintessence stars in the presence of cloud of strings to ensure the stability and physical presence of compact models. To achieve this goal, we studied features such as energy density, quintessence density, pressure profiles, gradients, anisotropic factor, energy conditions, sound speeds, TOV forces, EoS components, mass function, compactification and redshift. [ABSTRACT FROM AUTHOR]

The jet composition of GRB plays an important role in understanding the energy dissipation and radiation mechanisms in GRB physics, but it is poorly constrained from the observational data. Recently, an interesting long-duration GRB 230307A with redshift z  = 0.065 has attracted great attention. The lack of detected thermal emission and mini-structure of prompt emission light curve of this burst suggest that the outflow is Poynting-flux-dominated and point towards the ICMART model. In this paper, we invoke two independent methods to investigate the jet composition of GRB 230307A. The high magnetization parameter (σ > 7 or ever large) for R 0 = 1010 cm that is used to suppress thermal component, strongly suggests that a significant fraction of the outflow energy is likely in a Poynting flux entrained with the baryonic matter. Moreover, it is found that the radiation efficiency of this burst for typical values ϵ e  = 0.1 and ϵ B  = 0.01 can reach as high as |$~50{{\ \rm per\ cent}}$| which disfavours the internal shock model, but is consistent with ICMART model. Finally, a possible unified picture to produce GRB 230307A originated from a compact star merger is also discussed. [ABSTRACT FROM AUTHOR]

We address the crustal properties of neutron stars, such as crustal mass, crustal radius, crustal fraction of the moment of inertia and investigate the crustal and structural properties related to the glitching mechanism observed in pulsars. The mass, radius and crustal fraction of the moment of inertia in neutron stars have been determined using β -equilibrated neutron–proton–electron–muon (npe μ ) dense neutron star matter obtained using the extended Skyrme effective interactions with NRAPR and Brussels–Montreal parameter sets. The maximum mass of the neutron star calculated from these sets is able to reach ∼ 2 M ⊙ and higher, corroborating the recently observed masses of compact stars. The crustal fraction of the moment of inertia depends sensitively on the pressure and the corresponding density at the core–crust transition. The core–crust transition density and pressure together with the extracted minimum crustal fraction of the total moment of inertia provide a limit for the radii of pulsars. Present calculations imply that due to the crustal entrainment, the crustal fraction of the total moment of inertia is about 5.5 % . [ABSTRACT FROM AUTHOR]

In this study, we investigate the literature on anisotropic stellar spheres in f (R , ϕ) gravity utilizing Tolman–Kuchowicz (TK) spacetime. Due to the existence of anisotropic matter distribution, we derive the equations of motion for spherically symmetric spacetime by taking into account physically accurate formulations of the metric potentials. For this purpose, we develop the matching conditions by comparing them with the exterior solution to determine the TK constants. We have also discussed the graphical analysis of energy density, pressure components, equation of state components, equilibrium condition, and stability analysis. Moreover, other properties of a compact star, like the mass–radius function, compactness, and redshift function, have also been investigated. It is also noticed that energy conditions are satisfied, which justifies that our considered stars are viable. The validity of our proposed model has been proven by studying the development of various physical characteristics, and it is determined that our system is physically stable and free of any singularities. [ABSTRACT FROM AUTHOR]

ω Centauri is considered the most massive globular cluster of the Milky Way and likely the former nuclear star cluster of a Galaxy accreted by the Milky Way. It is speculated to contain an intermediate-mass black hole (IMBH) from several dynamical models. However, uncertainties regarding the location of the cluster centre or the retention of stellar remnants limit the robustness of the IMBH detections reported so far. In this paper, we derive and study the stellar kinematics from the highest-resolution spectroscopic data yet, using the Multi Unit Spectroscopic Explorer (MUSE) in the narrow field mode and wide field mode. Our exceptional data near the centre reveal for the first time that stars within the inner 20 arcsec (∼0.5 pc) counter-rotate relative to the bulk rotation of the cluster. Using this data set, we measure the rotation and line-of-sight velocity dispersion profile out to 120 arcsec with different centres proposed in the literature. We find that the velocity dispersion profiles using different centres match well with those previously published. Based on the counter–rotation, we determine a kinematic centre and look for any signs of an IMBH using the high-velocity stars close to the centre. We do not find any significant outliers >60 km s−1 within the central 20 arcsec, consistent with no IMBH being present at the centre of ω Centauri. A detailed analysis of Jeans' modelling of the putative IMBH will be presented in the next paper of the series. [ABSTRACT FROM AUTHOR]

We present the first results of the Dragon-II simulations, a suite of 19 N -body simulations of star clusters with up to 106 stars, with up to 33 per cent of them initially paired in binaries. In this work, we describe the main evolution of the clusters and their compact objects (COs). All Dragon-II clusters form in their centre a black hole (BH) subsystem with a density 10−100 times larger than the stellar density, with the cluster core containing |$50{-}80~{{\rm per\ cent}}$| of the whole BH population. In all models, the BH average mass steeply decreases as a consequence of BH burning, reaching values 〈 m BH〉 < 15 M⊙ within 10−30 relaxation times. Generally, our clusters retain only BHs lighter than 30 M⊙ over 30 relaxation times. Looser clusters retain a higher binary fraction, because in such environments binaries are less likely disrupted by dynamical encounters. We find that BH–main-sequence star binaries have properties similar to recently observed systems. Double CO binaries (DCOBs) ejected from the cluster exhibit larger mass ratios and heavier primary masses than ejected binaries hosting single CO binaries (SCOBs). Ejected SCOBs have BH masses m BH = 3−20 M⊙, definitely lower than those in DCOBs (m BH = 10−100 M⊙). [ABSTRACT FROM AUTHOR]

WDs and neutron stars are far-reaching and multi-faceted laboratories in the hunt for dark matter. We review detection prospects of wave-like, particulate, macroscopic and black hole dark matter that make use of several exceptional properties of compact stars, such as ultra-high densities, deep fermion degeneracies, low temperatures, nucleon superfluidity, strong magnetic fields, high rotational regularity, and significant gravitational wave emissivity. Foundational topics first made explicit in this document include the effect of the "propellor phase" on neutron star baryonic accretion, and the contribution of Auger and Cooper pair breaking effects to neutron star heating by dark matter capture. [ABSTRACT FROM AUTHOR]

Standard sirens have been the central paradigm in gravitational‐wave cosmology so far. From the gravitational wave signature of compact star binaries, it is possible to measure the luminosity distance of the source directly, and if additional information on the source redshift is provided, a measurement of the cosmological expansion can be performed. This review article discusses several methodologies that have been proposed to use gravitational waves for cosmological studies. Methods that use only gravitational‐wave signals and methods that use gravitational waves in conjunction with additional observations such as electromagnetic counterparts and galaxy catalogs will be discussed. The review also discusses the most recent results on gravitational‐wave cosmology, starting from the binary neutron star merger GW170817 and its electromagnetic counterpart and finishing with the population of binary black holes, observed with the third Gravitational‐wave Transient Catalog GWTC–3. [ABSTRACT FROM AUTHOR]

We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV metric (M.C. Durgapal, J. Phys. A: Math. Gen. 15, 2637 (1982)). In this work, we investigate the effects of the scale parameter k on the local matter distribution. Here, we have chosen the compact star candidate SMC X-1 with observed values of mass = (1.29 ± 0.05) M⊙ and radius = 8. 831 − 0.09 + 0.09 km, respectively, to analyze our results analytically as well as graphically. For smaller values of k, we get the stiff (or hard) equation of state (EoS). Here, we solve the modified Einstein field equations in the presence of the background metric γμν. Due to this constant curvature background, the density and pressure terms are modified by adding an extra term, which affects the EoS. For r ≪ k, the background de Sitter space–time reduces into Minkowski form, and the coupling vanishes. We discuss certain physical quantities of our obtained solution, such as density, isotropic pressure, sound speed, pressure-density gradients, compactness, and surface redshift, to claim the physical viability of our model. It is found that our model clearly satisfies all the energy conditions, the causality condition, and the dynamical equilibrium via a modified Tolman–Oppenheimer–Volkov equation. Finally, we can conclude that our proposed model is physically realistic and well behaved. [ABSTRACT FROM AUTHOR]

The Generalized Uncertainty Principle (GUP) is motivated by the premise that spacetime fluctuations near the Planck scale impose a lower bound on the achievable resolution of distances, leading to a minimum length. Inspired by a semiclassical method that integrates the GUP into the partition function by deforming its phase space, we induce a modification on the thermodynamic quantities of the MIT bag model that we propose serves as an effective semiclassical description of deconfined quark matter in a space with minimal length. We investigate the consequences of this deformation on the zero‐temperature limit, revealing a saturation limit for the energy density, pressure, and baryon number density and an overall decrease of the thermodynamic quantities which suggests an enhanced stability against gravitational collapse. These findings extend existing research on GUP‐deformed Fermi gases. Ultimately, our description introduces the effects of quantum gravity in the equations of state for compact stars in a mathematically simple manner, suggesting the potential for extension to more complex systems. [ABSTRACT FROM AUTHOR]

In this paper, we obtain a new class of stationary axisymmetric spacetimes by using the Gürses–Gürsey metric with an appropriate mass function in order to generate a rotating core of matter that may be smoothly matched to the exterior Kerr metric. The same stationary spacetimes may be obtained by applying a slightly modified version of the Newman–Janis algorithm to a nonrotating spherically symmetric seed metric. The starting spherically symmetric configuration represents a nonisotropic de Sitter-type fluid whose radial pressure p r satisfies an state equation of the form p r = − ρ , where the energy density ρ is chosen to be the Tolman-type-VII energy density [R. C. Tolman, Phys. Rev.55, 364 (1939)]. The resulting rotating metric is then smoothly matched to the exterior Kerr metric, and the main properties of the obtained geometries are investigated. All the solutions considered in this study are regular in the sense they are free of curvature singularities. Depending on the relative values of the total mass m and rotation parameter a, the resulting stationary spacetimes represent different kinds of rotating compact objects such as regular black holes, extremal regular black holes, and regular starlike configurations. [ABSTRACT FROM AUTHOR]

Stars embedded in active galactic nucleus (AGN) discs or captured by them may scatter onto the supermassive black hole (SMBH), leading to a tidal disruption event (TDE). Using the moving-mesh hydrodynamics simulations with arepo , we investigate the dependence of debris properties in in-plane TDEs in AGN discs on the disc density and the orientation of stellar orbits relative to the disc gas (pro- and retro-grade). Key findings are: (1) Debris experiences continuous perturbations from the disc gas, which can result in significant and continuous changes in debris energy and angular momentum compared to 'naked' TDEs. (2) Above a critical density of a disc around an SMBH with mass M • [ρcrit ∼ 10−8 g cm−3 (M •/106 M⊙)−2.5] for retrograde stars, both bound and unbound debris is fully mixed into the disc. The density threshold for no bound debris return, inhibiting the accretion component of TDEs, is |$\rho _{\rm crit,bound} \sim 10^{-9}{\rm g~cm^{-3}}(M_{\bullet }/10^{6}\, {\rm M}_{\odot })^{-2.5}$|⁠. (3) Observationally, AGN-TDEs transition from resembling naked TDEs in the limit of ρdisc ≲ 10−2ρcrit,bound to fully muffled TDEs with associated inner disc state changes at ρdisc ≳ ρcrit,bound, with a superposition of AGN + TDE in between. Stellar or remnant passages themselves can significantly perturb the inner disc. This can lead to an immediate X-ray signature and optically detectable inner disc state changes, potentially contributing to the changing-look AGN phenomenon. (4) Debris mixing can enrich the average disc metallicity over time if the star's metallicity exceeds that of the disc gas. We point out that signatures of AGN-TDEs may be found in large AGN surveys. [ABSTRACT FROM AUTHOR]

In this work, we consider the vanishing complexity factor scenario which has opened up a whole new way of generating solutions to the Einstein field equations for the spherically symmetric structure of celestial bodies. By using this very rare condition on the system of two metric potentials, viz. gtt and grr , we make reduce it to a uni-metric potential system satisfying all physical conditions. Along with this, we further have considered that the space–time is deformed by dark matter (DM) content in DM haloes resulting into perturbations in the gtt and grr metric potentials. This DM deformation is mathematically done by the complete geometric decoupling method where the decoupling parameter β decides the amount of DM content. In connection to the claimed post-merger object in the GW170817 event we have argued that if these compact stars were in galactic DM haloes with the assumption that the radius remains the same, the compactness factor can grow within the range 1/3 to 4/9 and therefore can generate gravitational waves (GW) echoes. Additionally, we have presented effect of β on the generation of GW echoes in accordance with the observational constraints related to the compact stars GW190814, PSR J0740+6620, PSR J1614−2230, Cen X-3, and LMC X-4. [ABSTRACT FROM AUTHOR]

We present a catalogue of 62 polluted white dwarfs observed by the 9th Low-Resolution Data Release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST LRS DR9v1; R ≈1800) and the Early Data Release 3 (EDR3) of the Gaia Mission. Among these stellar remnants, 30 are new discoveries with previously unknown traces of calcium pollution. To generate our catalogue, we used a data base of 4324 unique Gaia EDR3 white dwarf candidates with LAMOST LRS DR9v1 observations, many of which have been spectroscopically confirmed by other telescopes. For these stars, we developed a quantitative method to detect calcium absorption in their spectra between 3900–4000 Å, which we then validated through visual inspection and multiple literature cross-checks. Our catalogue provides the astrometric and photometric properties of the white dwarf candidates, incorporates supplementary data (e.g. Montreal White Dwarf Database, MWDD; PanSTARRS; the Hubble Space Telescope), and indicates the possibility of calcium pollution in their atmospheres. For our final sample of polluted white dwarfs, we also determine the main atmospheric properties of 23 sources with effective temperatures T eff ≤ 25 000 K and no existing calcium abundances in the MWDD. Our analysis represents a first step towards measuring the full atmospheric composition of these stars and learning about the bulk properties of their accreted material. As we venture into the era of wide-field spectroscopic surveys, our work highlights the importance of combining large-scale data bases for identifying and characterizing new polluted white dwarfs. [ABSTRACT FROM AUTHOR]

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 + 0.30 M ⊙ and radius = 9.8 ± 1.8 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. [ABSTRACT FROM AUTHOR]

In this article, a new class of exact solutions for anisotropic compact objects is presented. Admitting the modified Chaplygin equation of state p = H ρ - K ρ n , where H, K and n are constants with 0 < n ≤ 1 , and employing the Buchdahl-I metric within the framework of the general relativity stellar model is obtained. Recent observations on pulsars and GW events reveal that the observed maximum mass of compact stars detected so far is approximately 2. 59 - 0.09 + 0.08 M ⊙ . Since massive stars cannot be supported by a soft equation of state, a constraint of the equation of state must hold. The choice of a suitable equation of state for the interior matter of compact objects may predict useful information compatible with recent observations. TOV equations have been solved using the modified Chaplygin equation of state to find the maximum mass in this model. In particular, the theory can achieve 3.72 M ⊙ , when H = 1.0 , K = 10 - 7 and n = 1 . The model is suitable for describing the mass of pulsars PSR J2215+5135 and PSR J0952-0607 and the mass 2. 59 - 0.09 + 0.08 M ⊙ of the companion star in the GW 190814 event. The 3.72 M ⊙ is hardly achievable theoretically in general relativity considering fast rotation effects too. To check the physical viability of this model, we have opted for the stability analysis and energy conditions. We have found that our model satisfies all the necessary criteria to be a physically realistic model. [ABSTRACT FROM AUTHOR]

This study examines Einstein's field equations in the context of general relativity, comparing five distinct methodologies: (a) vanishing complexity, (b) embedding class one or the Karmarkar condition, (c) conformally flat spacetime, (d) conformal killing symmetry, and (e) the Karmarkar scalar condition. The first four methods reveal a significant connection between two metric potentials, while the fifth method provides a coordinate-independent condition expressed in terms of structural scalars. The paper provides a comprehensive comparative analysis of a new exact solution derived by assuming a common metric function and solving the remaining metric functions through corresponding bridge equations to evaluate their effectiveness and validity. Critical parameters such as thermodynamic factors, causality conditions, stability, and mass function analysis are investigated. [ABSTRACT FROM AUTHOR]

In this paper, we study the viability and stability of anisotropic compact stars in the context of f (Q) theory, where Q is non-metricity scalar. We use Finch–Skea solutions to investigate the physical properties of compact stars. To determine the values of unknown constants, we match internal spacetime with the exterior region at the boundary surface. Furthermore, we study the various physical quantities, including effective matter variables, energy conditions and equation of state parameters inside the considered compact stars. The equilibrium and stability states of the proposed compact stars are examined through the Tolman–Oppenheimer–Volkoff equation, causality condition, Herrera cracking approach and adiabatic index, respectively. It is found that viable and stable compact stars exist in f (Q) theory as all the necessary conditions are satisfied. [ABSTRACT FROM AUTHOR]

This article focuses on investigating the role of decoupling in isotropizing anisotropic, self-gravitational charged sources with spherical symmetry through a well-known gravitational technique, known as minimal geometric deformation (MGD). This technique separates the given system into two gravitational systems: the Einstein-Maxwell system and the gravitational system governed by additional source. We employ novel approaches, including the zero complexity factor and isotropization techniques, to construct various charged compact star models using the Tolman IV as the seed source within the framework of the MGD scheme. The term complexity factor emerges as one of the structure-defining scalar quantities resulting from the orthogonal splitting of the Riemann–Christoffel curvature tensor, as proposed by Herrera (Phys Rev D 97(4):044010, 2018). This scalar function, denoted as Y TF , is associated with the fundamental structural characteristics of self-gravitational compact configurations. Our approach is innovative in that it derives the deformation functions by imposing the requirement of Y TF = 0 and employs isotropization techniques for electrically charged anisotropic configurations. [ABSTRACT FROM AUTHOR]

In the context of the f(Q)$f(Q)$ theory of gravity, a spherically symmetric quintessence DE model in this article is offered. For this reason, f(Q)$f(Q)$ has the formula f(Q)=aQ2+Q$f(Q)=aQ^2+Q$, where Q stands for the non‐metricity scalar and 'a' is the coupling constant for modified gravity has been taken into account. It is supposed that the quintessence field defined by the parameter ωq$\omega _q$, where ωq∈(−1,−13)$\omega _q \in (-1,\,-\frac{1}{3})$, controls the energy‐momentum tensor of the underlying fluid distribution. The relationship between several physical parameters for the selected values of 'a', by choosing the metric potentials suggested by the Krori‐Barua [Krori and Barua; J. Phys. A, Math. Gen. 8: 508, 1975] is investigated. Further, a number of analyses in detail to examine the physical validity of the proposed stellar model are carried out. The consequences of the compact star system caused by the connection of matter and geometry are succinctly described. The maximum allowable mass and radius for our present model for different values of 'a' have been studied by M−R$M-R$ and M−ρc$M-\rho _c$ curve. One can recover the usual general relativity (GR) standard results for a=0$a=0$. In the context of the f(Q)$f(Q)$ theory of gravity, a spherically symmetric quintessence DE model in this article is offered. For this reason, f(Q)$f(Q)$ has the formula f(Q)=aQ2+Q$f(Q)=aQ^2+Q$, where Q stands for the non‐metricity scalar and 'a' is the coupling constant for modified gravity has been taken into account. It is supposed that the quintessence field defined by the parameter ωq$\omega _q$, where ωq∈(−1,−13)$\omega _q \in (-1,\,-\frac{1}{3})$, controls the energy‐momentum tensor of the underlying fluid distribution. The relationship between several physical parameters for the selected values of 'a', by choosing the metric potentials suggested by the Krori‐Barua [Krori and Barua; J. Phys. A, Math. Gen. 8: 508, 1975] is investigated. Further, a number of analyses in detail to examine the physical validity of the proposed stellar model are carried out. The consequences of the compact star system caused by the connection of matter and geometry are succinctly described. The maximum allowable mass and radius for our present model for different values of 'a' have been studied by M−R$M-R$ and M−ρc$M-\rho _c$ curve. One can recover the usual general relativity (GR) standard results for a a=0$a=0$. [ABSTRACT FROM AUTHOR]

The orbital eccentricity is one of the key parameters to describe the orbit of celestial bodies, which can provide important clues to reveal their dynamical evolution, and thus help to understand their formation and evolution processes along with the physical mechanisms behind them. The continuous improvement of observational technologies, enable us to explore the orbit of celestial bodies beyond the solar system, i.e., from stellar systems to planetary systems. Focusing on the orbital eccentricity of celestial bodies, this paper reviews the progress in stellar systems (including the main sequence stars, brown dwarfs, and compact stars) and planetary systems (including gas-giants, low-mass exoplanets such as "super-Earth" and "sub-Neptune"), and summarizes several similarities and issues among the investigations of orbital eccentricity under different scales. Finally, based on the ongoing and future astronomical facilities and missions, we discuss the future prospect on eccentricity studies of stellar systems, extra-solar planetary systems, and even extra-solar satellite systems. [ABSTRACT FROM AUTHOR]

We report measurements of H  i content in 11 nearby, actively star-forming, blue compact dwarf galaxies (BCDs) from 21 cm observations with the Arecibo telescope. These BCDs, selected by their red (W2[4.6  |$\mu$| m]−W3[12  |$\mu$| m]>3.8 mag) and bright mid-infrared (MIR) emission (W4[22  |$\mu$| m]<7.6 mag), have high specific star formation rates (median sSFR ∼10−7.8 yr−1), similar to high redshift galaxies. H  i emission was detected in six sources. We analyse our new detections in the context of previous H  i observations of 218 dwarf irregulars (dIs) and BCDs in the literature. The M H  i – M * relation resulting from our observations confirms the dominating fraction of H  i gas among baryons in galaxies with lower stellar masses. This Arecibo BCD sample has significantly lower median H  i depletion time-scales (τ H i ∼ 0.3 Gyr) than other dIs/BCDs (∼ 6.3 Gyr) in the literature. The majority of the sources (10/11) in the Arecibo sample are very red in W1[3.4  |$\mu$| m]−W2[4.6  |$\mu$| m] colour (>0.8 mag) implying the presence of warm dust. We investigate the relation of τHI with stellar mass (M *) and sSFR. We find that τH  i is significantly anticorrelated with M * for higher sSFR (>10−8.5 yr−1) and with sSFR for higher stellar mass (⁠|$\gt 10^{7.5}\, {\rm M}_{\odot }$|⁠) dwarf galaxies. The high sSFR for the BCDs in the Arecibo observed sample is mainly due to their high atomic gas star formation efficiency (SFE) or low τH  i . The low τH  i or high SFE in these sources is possibly due to runaway star formation in compact and dense super star clusters. [ABSTRACT FROM AUTHOR]

We present evidence for a 0.278(8) d ( =6.7 h) orbital period in the X-ray transient GRS 1716-249 (=N Oph 93), based on a superhump modulation detected during the 1995 mini-outburst plus ellipsoidal variability in quiescence. With a quiescent magnitude of r  = 23.19 ± 0.15 N Oph 93 is too faint to warrant a full dynamical study through dedicated time-resolved spectroscopy. Instead, we apply the FWHM– K 2 correlation to the disc H α emission line detected in Gran Telescopio Canarias spectra and obtain K 2 = 521 ± 52 km s−1. This leads to a mass function f (M) = 4.1 ± 1.2 M⊙, thus indicating the presence of a black hole in this historic X-ray transient. Furthermore, from the depth of the H α trough and the quiescent light curve we constrain the binary inclination to i  = 61 ± 15°, while the detection of superhumps sets an upper limit to the donor to compact star mass ratio q  = M 2/ M 1 ≲ 0.25. Our de-reddened (r − i) colour is consistent with a ≈ K6 main sequence star that fills its Roche lobe in a 0.278 d orbit. Using all this information we derive a compact object mass |$M_{1}=6.4^{+3.2}_{-2.0}$| M⊙ at 68 per cent confidence. We also constrain the distance to GRS 1716-249 to 6.9 ± 1.1 kpc, placing the binary ∼0.8 kpc above the Galactic Plane, in support of a large natal kick. [ABSTRACT FROM AUTHOR]

The Teleparallel Theory is equivalent to General Relativity, but whereas in the latter gravity has to do with curvature, in the former gravity is described by torsion. As is well known, there is in the literature a host of alternative theories of gravity, among them the so called extended theories, in which additional terms are added to the action, such as for example in the f(R) and f(T) gravities, where R is the Ricci scalar and T is the scalar torsion, respectively. One of the ways to probe alternative gravity is via compact objects. In fact, there is in the literature a series of papers on compact objects in f(R) and f(T) gravity. In particular, there are several papers that consider f (T) = T + ξ T 2 , where ξ is a real constant. In this paper, we generalise such extension considering compact stars in f (T) = T + ξ T β gravity, where ξ and β are real constants and looking out for the implications in their maximum masses and compactness in comparison to the General Relativity. Also, we are led to constrain the β parameter to positive integers which is a restriction not imposed by cosmology. [ABSTRACT FROM AUTHOR]

We investigate a few models with various physical elements that could lead to the appearance of celestial bodies with different curvature systems within the background of f (R , G) gravity, where R represents the Ricci scalar and G stands for the Gauss–Bonnet curvatures. After formulating f (R , G) field equations in the setting of anisotropic fluid configuration, along with specific metric coefficients, the observational data of HerX − 1, 4U1820 − 30, VeLAX − 1, SAXJ1808.4 − 3068, CenX − 3, and PSRJ16142230 are used. Three different gravity models are used to analyze their impact on mathematical modeling. Several physical factors have been illuminated, including energy density, pressure evolutions, energy conditions, stability analysis, the measurement equation of state parameters, matter content, etc. To access the substance of our model, we observed a number of physical factors, and it was discovered that our system does not contain any singularities. [ABSTRACT FROM AUTHOR]

This work deals with the investigation of several physical elements that contribute to the construction of stellar objects in the f (R , G) theory, where R and G symbolize the Ricci and Gauss–Bonnet scalars, respectively. In the presence of an anisotropic source, we offer the fundamental formalization of this modified theory. To establish the physical viability of our models, we employ various methods. Energy conditions (ECs) will be derived to ensure the physical validity of our models within the context of f (R , G) gravity. Moreover, we examine the physical viability through the assessment of radial and tangential sound speeds. Additionally, we analyze the equation of state (EoS) parameter and the anisotropic factor in the presence of the electromagnetic field's influence. Dense stars are shown to be stable under anisotropy measures and exhibit their physical behavior under anisotropic stresses. We identify regions where the systems occupy high compactness and maintain stable ECs with a particular electric charge contribution. [ABSTRACT FROM AUTHOR]