arXiv subjects

A. Errehymy

Publications and source records attributed to A. Errehymy.

16 recordsLinked to original sources

arXiv2026

Joint Constraints on Quantum Oppenheimer--Snyder Black Holes from High-Frequency Quasi-Periodic Oscillations in X-ray Binary Systems and the S2 Star Orbit

We study a quantum-corrected version of the Oppenheimer--Snyder (OS) spacetime in which classical collapse is modified by a single effective-parameter $α$, representing small-quantum-gravitational effects in a phenomenologically rescaled-form. Although the correction enters through a term proportional to $αM^2/r^4$, it produces noticeable changes in the strong-field region while leaving weak-field physics almost unchanged. One of the main results is the appearance of a minimum-mass for horizon-formation, $M_{\min} \sim(0.5-1.2)\,M_\odot$ for the effective-parameter $α\approx0.22$. We emphasize that this $M_{\min}$ is expressed in terms of the effective-parameter $α$; in terms of the bare loop-quantum-gravity (LQG) parameter, $M_{\min}\sim M_{\text{Pl}}\sim10^{-5}$~g, consistent with the theoretical-expectation. Orbital properties are also slightly modified, with the innermost-stable-circular-orbit (ISCO) shifting to $r_{\rm ISCO}=6M-α/(12M)$, giving corrections-of-order $ \sim 10^{-4} $ for stellar-black-holes and $\sim 10^{-10}$ for Sgr A$^\ast$. In the same region, radial epicyclic frequencies change by about $5\%-10\%$ near $r\sim5M$, while vertical modes are less affected, leading to small but structured shifts in quasi-periodic oscillation (QPO) behavior. Using four X-ray binaries (GRS 1915+105, XTE J1550-564, XTE J1859+226, GRO J1655-40), we find a consistent range $α=0.22\pm0.10$, with masses between $5.4-12.4\,M_\odot$ and emission radii $r/M \sim 5.5 - 8.6$. The observed QPO frequencies, lying in the range $100-450$ Hz, are well reproduced within this framework. Weak-field tests such as S2 and Mercury still allow $f_{\rm sp}=1.10 \pm 0.19$, leaving room for these small strong-gravity corrections.

gr-qc↗

arXiv2026

Observational Limits on Einasto Dark Matter Parameters from Event Horizon Telescope Images of Sgr A$^{}$ and M87$^{}$

The Event Horizon Telescope (EHT) has provided images of the supermassive black-holes Sgr A$^{*}$ and M87$^{*}$, enabling direct tests of gravity. Any extended mass-distribution, such as a dark-matter halo, perturbs null-geodesics in the photon-ring regime, making shadow-measurements a probe of inner-halo structure. In this work, we investigate static, spherically-symmetric black-holes surrounded by Einasto-type dark-matter halos and derive constraints from EHT shadow-data. Starting from the Einasto density-profile with parameters ${\varrho_0, \tildeα, \tildeν}$, we construct a metric-function $f(r)=1-2M/r+2M_\infty \tilde{g}(r)$ that interpolates between the black-hole horizon and the asymptotic halo, following the approach of Xu et al. (2018) but adapted specifically to the Einasto scenario. We analyze the photon-potential, null-geodesics, and shadow-radius as functions of black-hole mass $M$, in the non-spinning limit. Using the dimensionless shadow-diameter $d_{\text{sh}}\equiv Dθ/M$ measured by the EHT -- $d_{\text{sh}}^{M87*}=11.0\pm1.5$ and $d_{\text{sh}}^{SgrA*}=9.5\pm1.4$ -- we perform Bayesian parameter-estimation to identify allowed regions in the Einasto parameter-space. Combined with the independently-measured black-hole masses from stellar-dynamics, our results place constraints on the inner dark-matter distribution: for Sgr A$^{*}$, adopting the stellar-orbit mass-prior, we find $\varrho_0 \lesssim 10^{-11},M_\odot/\text{pc}^3$ at $1σ$ confidence, while for M87$^{*}$ the bounds are weaker due to distance-uncertainties. The Einasto-index $\tildeν$ is weakly-constrained, indicating that EHT precision primarily limits the mass enclosed near the photon-sphere rather than the profile-slope. Future EHT observations will refine these constraints and distinguish between competing dark-matter descriptions.

gr-qc↗

arXiv2026

Observational Constraints on Kazakov-Solodukhin Quantum-Deformed Black Holes from M87$^$ and Sgr A$^$ Shadows

We explore the Kazakov-Solodukhin quantum-deformed black hole spacetime, characterized by a single deformation parameter $ η$ that encodes quantum corrections to the classical Schwarzschild solution. The model preserves the correct general-relativistic limit as $ η\to 0 $, while introducing significant and physically meaningful deviations in the strong-field regime. A central and remarkable feature of the geometry is the regularization of the classical singularity: curvature invariants remain finite near the minimal radius $ r = η$, effectively replacing the divergent core with a smooth and well-behaved region. This behavior naturally introduces a minimal length scale into the spacetime structure, offering a geometrically motivated resolution of the singularity problem. The deformation modifies the horizon structure, shifts the event horizon location, and alters the mass-radius relation. It also reduces the surface gravity, leading to a lower Hawking temperature and a slower evaporation process, thereby enhancing the thermodynamic stability of the black hole. Photon dynamics are correspondingly affected, resulting in a displaced photon sphere and modified strong-lensing characteristics. While the shadow remains perfectly circular due to spherical symmetry, its size depends sensitively on $ η$. Observational constraints can be expressed through $ \left| R_{sh}(η) - R_{obs} \right| \leq ΔR_{obs}, $ which places an upper bound on the deformation parameter. In the weak-field limit, the deflection angle acquires a quadratic correction proportional to $ η^2 $, ensuring consistency with precision tests while allowing potentially detectable deviations in strong-gravity observations. These features make the model both theoretically appealing and observationally testable.

gr-qc↗

arXiv2026

Slowly rotating traversable wormholes supported by radially varying string-fluid matter: From regular geometries to photon trajectories

This work investigates slowly rotating traversable wormholes supported by string fluids whose properties vary with distance from the throat. This radial variation allows the matter to transition smoothly from a de Sitter-like core near the center to a string-dominated environment further out, producing a regular, horizon-free, and asymptotically flat spacetime. By letting the transverse pressure depend on radius, the fluid naturally adapts to the surrounding geometry, resulting in a well-behaved energy density and shape function. Even modest rotation introduces frame-dragging effects that gently twist photon paths, creating subtle differences between co-rotating and counter-rotating trajectories. These effects are strongest near the throat, while at larger distances the spacetime is largely governed by the static gravitational potentials. Circular photon orbits reveal that the interplay of the redshift function, wormhole shape, and rotation shapes the photon-sphere structure. Different radial profiles of the string fluid generate distinctive photon-ring patterns, offering potential observational signatures of both the rotation and the internal matter distribution. Overall, radially varying string fluids provide a flexible and physically consistent source for traversable wormholes, bridging smoothly between vacuum-like and string-dominated regions while maintaining regularity and supporting slow rotation. This study highlights how anisotropic matter can influence both curvature and light propagation, providing a realistic framework for horizonless exotic spacetimes and suggesting new avenues to explore subtle observational effects around traversable wormholes.

gr-qc↗

arXiv2026

Holographic dark energy as a source for slowly rotating wormholes: Implications for null geodesics and shadows

In this work, we explore for the first time slowly rotating traversable wormholes embedded in holographic dark energy. We focus on three representative holographic dark energy models -- Rényi, mixed, and Moradpour -- and construct the wormhole shape functions directly from these energy density profiles using a Teo-type rotating wormhole metric. This allows us to examine the wormhole geometry in detail, including throat structure, the flaring-out condition for safe traversal, and violations of the null energy condition. To capture the effects of different redshift behaviors, we consider three smooth hyperbolic redshift functions -- Sinh, Cosh, and Tanh -- and study how they influence photon motion, null geodesics, effective potentials, photon-sphere locations, and Lense-Thirring precession caused by wormhole rotation. Our analysis shows that cuspy Rényi profiles produce tighter photon orbits and stronger asymmetry, while smoother mixed and Moradpour profiles allow more circular paths and weaker frame-dragging effects. Finally, we calculate the shadows cast by these wormholes, finding that Rényi-supported wormholes generate smaller, asymmetric shadows, whereas mixed and Moradpour-supported wormholes produce larger, nearly circular silhouettes. Altogether, this study provides a detailed theoretical picture of photon dynamics, shadow morphology, and relativistic effects in slowly rotating wormholes within realistic holographic dark energy environments, offering potential guidance for observational signatures of these exotic objects.

gr-qc↗

arXiv2026

Probing geometrically perturbed strange stars with minimal decoupling using millisecond pulsar timing observations

We construct a gravitationally decoupled anisotropic strange star model using the minimal geometric deformation approach with a MIT bag equation of state and an additional source sector controlled by a deformation parameter $β$ and a radial perturbation scale $Ψ$ through $g(r)=\sin(Ψr^{2})$. The resulting Einstein system is consistently split into seed and $θ$-sectors and matched to an exterior Schwarzschild geometry. The model is constrained by high-mass pulsars: PSR J0740+6620 $(2.08\pm0.07\,M_\odot)$, PSR J1810+1744 $(2.13\pm0.04\,M_\odot)$, PSR J1959+2048 $(2.18\pm0.09\,M_\odot)$, and PSR J2215+5135 $(2.28^{+0.10}_{-0.09}\,M_\odot)$. It reproduces these objects with predicted radii $R \approx 11.3$--$12.9$ km. The maximum mass reaches $M_{\max} \approx 2.28\,M_\odot$ for $β= 3\times 10^{-3}$ and $Ψ\approx 0.03\,\text{km}^{-2}$, while for $β= 10^{-3}$ the configuration yields $M_{\max} \approx 2.12\,M_\odot$ with $R \approx 12.2$ km. The central density lies in $ρ_c \approx (2.4$--$3.1)\times 10^{-4}\,\text{km}^{-2}$, decreasing smoothly to $ρ_s \approx 2.0\times 10^{-4}\,\text{km}^{-2}$. The anisotropy increases from zero at the center to $Δ\approx (0.25$--$0.45)\times 10^{-4}\,\text{km}^{-2}$ near the surface, generating additional outward support that enhances compactness by $\sim 15\%$. The compactness parameter spans $C \approx 0.17$--$0.22$, safely below the Buchdahl limit, while the surface redshift reaches $z_s \approx 0.25$--$0.38$. The condition $dM/dρ_c > 0$ is satisfied throughout, confirming dynamical stability. Overall, $β$ enhances the maximum mass by up to $\sim 15\%$, while $Ψ$ introduces controlled oscillatory structure without violating observational constraints, producing stable ultra-compact stars consistent with current pulsar data.

gr-qc↗

arXiv2026

Dymnikova-Schwinger quantum-corrected slowly rotating wormholes: Photon and spinning particle dynamics

This work studies light propagation near slowly rotating traversable wormholes supported by a quantum-inspired matter source. The model is based on the Dymnikova density profile, viewed as a gravitational analogue of the Schwinger mechanism, which yields a smooth, non-singular core. Quantum effects are included through the generalized uncertainty principle (GUP), introducing a minimal length scale while preserving regularity. Within a stationary and axisymmetric framework, we construct rotating wormhole solutions sustained by the GUP-corrected Dymnikova-Schwinger profile. The geometry satisfies key conditions such as asymptotic flatness and the flare-out requirement, and incorporates rotational features like frame dragging. We then examine photon motion via null geodesics. Both rotation and quantum corrections modify the photon sphere structure, with rotation producing a splitting between co-rotating and counter-rotating trajectories. This results in small asymmetries in photon paths and the shadow. These results provide a novel and consistent framework to probe quantum-gravity imprints in strong-field optics.

gr-qc↗

arXiv2026

Event Horizon Telescope Observational Constraints on Dymnikova-Type Non-Singular Black Holes in Higher Dimensions

Black holes are among the most compelling predictions of general relativity (GR) and are now strongly supported by observations from gravitational-wave detectors and the Event Horizon Telescope (EHT). While standard black hole solutions suffer from central singularities, regular black holes avoid this issue by introducing a nonsingular core. In this work, we extend the Dymnikova regular black hole to higher dimensions using a smooth matter distribution. The resulting spacetime features a de Sitter-like core and two horizons. We analyze photon motion and show that circular photon orbits remain unstable, giving rise to a well-defined black hole shadow. Our results indicate that the shadow size grows with the black hole scale but decreases slightly as the number of dimensions increases. We also investigate thermodynamic properties, including Hawking temperature and energy emission, and find a strong dependence on dimensionality. Finally, we compare our model with EHT observations to place constraints on the parameters and highlight potential observational signatures of higher-dimensional regular black holes.

gr-qc↗

arXiv2025

Analytical and numerical study of accretion processes around charged spherically symmetric black holes in scalar-tensor Gauss-Bonnet gravity

We investigate the physical phenomena occurring around a spherically symmetric, non-rotating charged black hole (BH) to explore the effects of scalar-tensor Gauss-Bonnet gravity on circular motion, accretion disk properties, and Bondi-Hoyle-Lyttleton (BHL) accretion flow. By analytically and numerically examining the influence of the Gauss-Bonnet coupling constant $c_1$ and the cosmological parameter $Λ$, we reveal how these modified gravity parameters alter the underlying physical processes. Using geodesic analysis, we compute the specific energy, angular momentum, innermost stable circular orbit (ISCO) radius, and radiation flux of test particles, providing insight into how the modified gravity framework affects orbital stability and the organization of the accretion flow. Subsequently, through numerical solutions of the general relativistic hydrodynamic (GRHD) equations, we describe the morphology of the shock cone formed via the BHL accretion mechanism around the BH. The numerical results demonstrate that increasing the values of $c_1$ and negative $Λ$ reduce gravitational focusing. Consequently, depending on the parameter choices, the opening angle of the shock cone either widens or narrows compared to the Schwarzschild case. However, because of weakened gravitational focusing, both the amount of accreted matter and the density of material trapped inside the cone decrease significantly. These results indicate that scalar-tensor Gauss-Bonnet corrections act as an effective gravitational damping term, transferring turbulence and transforming shock-dominated accretion into more stable configurations. The consistency between theoretical and numerical results suggests that the observable properties of accretion disks and quasi-periodic oscillations (QPOs) can serve as probes to constrain the parameters of scalar-tensor Gauss-Bonnet gravity in strong-field regimes.

gr-qc↗

arXiv2025

Quantum corrections to Dymnikova-Schwinger black holes in Einstein-Gauss-Bonnet gravity

This work investigates black holes within a modified framework of gravity that incorporates quantum-inspired corrections and a fundamental minimal length scale. By integrating Einstein-Gauss-Bonnet gravity with a specially tailored matter source that models quantum particle creation, we derive novel, non-singular black hole solutions. These black holes exhibit rich horizon structures and, notably, do not undergo complete evaporation -- instead, they stabilize into permanent remnants. In addition to analyzing the thermodynamic implications of quantum corrections to Dymnikova-Schwinger black holes, we examine their quasinormal mode spectra using the WKB approximation, alongside their associated energy emission rates. Our findings provide compelling new perspectives on how quantum effects may address foundational issues such as the black hole information loss paradox.

gr-qc↗

arXiv2025

Role of cosmic voids and their matter properties in shaping wormhole geometry in generalized geometry-matter coupling gravity

Cosmic voids are increasingly recognized as a promising tool for cosmological exploration. Their distribution and density profiles are highly responsive to alterations in gravitational theories, along with the influences of dark energy and neutrinos. Investigating voids offers a compelling opportunity to uncover signatures of alternative gravity models on a cosmological level. Voids span a notable range of density contrasts, from approximately -$1$ near their centers to around $0$ at their edges, where screening mechanisms become less effective. The primary objective of this study is to explore a novel model that introduces a new category of wormhole solutions by leveraging cosmic voids$-$vast underdense regions of the universe$-$for the first time. We focus on identifying new exact static wormhole models by proposing an alternative viewpoint on their matter content, rooted in the recently formulated $f(R,\mathcal{L}_m,T)$ theory of gravity. By developing a unique solution based on a universal density profile for voids, we examine crucial constraints on the parameters that dictate matter distribution and the structure of spacetime itself. Our results reveal how these cosmic voids significantly influence the geometry of wormholes, steepening the gradient toward the throat and mitigating violations of the null and weak energy conditions, particularly beyond their centers. We also highlight intriguing gravitational lensing effects, showing that this wormhole repels light rather than capturing it, creating a fascinating interaction between gravity and light.

gr-qc↗

arXiv2025

Dehnen-type dark matter wormholes in the $f(\mathcal{R},\mathcal{L}_m,\mathcal{T})$ action

We are exploring the possibility of traversable wormholes existing in a more realistic context. Specifically, we are looking at scenarios that don't rely on exotic factors, like having a mass shell at the throat or allowing particles and antiparticles to coexist without annihilation. To do this, we are constructing wormholes with double power-law density distributions, drawing inspiration from the Dehnen-type dark matter halo in the framework of generalized geometry-matter coupling gravity. Our investigation carefully considers the challenges of traversability and stability, as well as the roles of exotic matter, the exoticity parameter, and the anisotropy parameter. We have discovered solutions that describe asymmetric, asymptotically flat traversable wormholes, supported by a smooth metric and double power-law density distributions. These solutions successfully avoid the problems, giving us hope that such wormholes could actually exist in nature.

gr-qc↗

arXiv2025

Relativistic massive compact stars supported by decoupled matter: Implications for mass-radius bounds

The merger of binary neutron stars (BNSs) is a remarkable astrophysical event where all four fundamental forces interplay dynamically across multiple stages, producing a rich spectrum of multi-messenger signals. These observations present a significant multiphysics modeling challenge but also offer a unique opportunity to probe the nature of gravity and the strong nuclear interaction under extreme conditions. The landmark detection of GW170817 provided essential constraints on the properties of non-rotating neutron stars (NSs), including their maximum mass (M_{max}) and radius distribution, thereby informing the equation of state (EOS) of cold, dense nuclear matter. While the inspiral phase of such events has been extensively studied, the post-merger signal holds even greater potential to reveal the behavior of matter at supranuclear densities, particularly in scenarios involving a transition to deconfined quark matter. Motivated by the recent gravitational wave event GW190814 (2.5-2.67 M_{\odot}), we revisit the modeling of high-mass compact stars to investigate their internal structure via a generalized polytropic EOS. This framework incorporates a modified energy density profile and is coupled with the TOV equations. We explore mass-radius (M-R) relationships within both GR and the minimal geometric deformation (MGD) approach. Specifically, we constrain the radii of four massive compact objects PSR J1614-2230 (1.97^{+0.04}_{-0.04}\,M_{\odot}), PSR J0952-0607 (2.35^{+0.17}_{-0.17}\,M_\odot), GW190814 (2.5-2.67\,M_\odot), and GW200210 (2.83^{+0.47}_{-0.42}\,M_\odot) and demonstrate that our theoretical M-R curves are consistent with observational data. These findings provide meaningful constraints on the EOS and underscore the potential of alternative gravity models to accommodate ultra-massive compact stars within a physically consistent framework.

gr-qc↗

arXiv2025

Possible wormholes in generalized geometry-matter coupling gravity induced by the Dekel-Zhao dark matter profile

In the late 1980s, Morris and Thorne led in theoretical physics by creating solutions to wormholes and formulating the crucial requirements for safe traversability of wormholes. They found that exotic matter must meet the requirement $P_r + ρ< 0$, where $P_r$ is radial pressure and $ρ$ is energy density. This is a rudimentary grasp of our understanding of general relativity. In this paper, we continue their excellent work by looking at how to build traversable wormhole solutions in an extended theory of gravity. We adopt a process of linearly modifying the matter Lagrangian and the energy-momentum tensor with some coupling strengths $λ$ and $χ$. This may be considered as a special case of linear $f(R, T)$ gravity with matter coupling variability or as an additively separable simple $f(R, L_m, T)$ model. We undertake a detailed analysis of static wormhole solutions with a constant redshift function. This allows us to present our results as a first-order approximation in the $f(R, L_m, T)$ scenario. We derive the wormhole shape function from the Dekel-Zhao dark matter distribution in such a way that our solutions satisfy the needed conditions for traversability as well as the requirement of exotic matter. This is particularly exciting as it shows that wormholes in $f(R, L_m, T)$ gravity can sustain both exotic as well as ordinary matter. To ensure that the shape function meets the requirement of flaring-out and is asymptotically flat, we place some constraints on the couplings. We also examine the gravitational lensing effects, which exhibit a repulsive gravitational force that appears in our extended gravity for positive couplings.

gr-qc↗

arXiv2025

Role of gravitational decoupling on theoretical insights of relativistic massive compact stars in the mass gap

Advancements in theoretical simulations of mass gap objects, particularly those resulting from neutron star mergers and massive pulsars, play a crucial role in addressing the challenges of measuring neutron star radii. In the light of this, we have conducted a comprehensive investigation of compact objects (CSs), revealing that while the distribution of black hole masses varies based on formation mechanisms, they frequently cluster around specific values. For instance, the masses observed in GW190814 $(23.2^{+1.1}_{-1.0} \, M_{\odot})$ and GW200210 $(24.1^{+7.5}_{-4.6} M_{\odot})$ exemplify this clustering. We employed the gravitational decoupling approach within the framework of standard general relativity and thus focusing on the strange star model. This model highlights the effects of deformation adjusted by the decoupling constant and the bag function. By analyzing the mass-radius limits of mass gap objects from neutron star mergers and massive pulsars, we can effectively constrain the free parameters in our model, allowing us to predict the radii and moments of inertia for these objects. The mass-radius ($M-R$) and mass-inertia ($M-I$) profiles demonstrate the robustness of our models. It is shown that as the decoupling constant $β$ increases from 0 to 0.1 and the bag constant $\mathcal{B}_g$ decreases from 70 $MeV/fm^3$ to 55 $MeV/fm^3$, the maximum mass reaches $M_{max} = 2.87 \, M_\odot$ with a radius of 11.20 km. In contrast, for $β= 0$, the maximum mass is $M_{max} = 2.48 \, M_\odot$ with a radius of 10.69 km. Similarly, it has been exhibited that as $β$ decreases to 0, the maximum mass peaks at $M_{max} = 2.95 M_\odot$ for $\mathcal{B}_g = 55 MeV/fm^3$ with a radius of 11.32 km. These results not only exceed the observed masses of CSs but also correlate with recent findings from gravitational wave events like GW190814 and GW200210.

astro-ph.HE↗

arXiv2024

Exploring accelerated expansion in the universe: A study of $f(Q,T)$ gravity with parameterized EoS and cosmological constraints

The study conducted in this research paper utilizes the $f(Q,T)$ gravity, where $Q$ represents non-metricity and $T$ represents the trace of the energy-momentum tensor, to investigate the accelerated expansion of the universe. To complete the study, an effective EoS with one parameter $α$, is parameterized as $ω_{eff}=-\frac{3}{α(1+z)^{3}+3}$. The linear version of $f(Q,T)=-Q+σT$ is also considered, where $σ$ is a constant. By constraining the model with six BAO points, 57 Hubble points, and 1048 Pantheon sample datasets, the parameters $α$ and $σ$ are determined to best match the data. The cosmological parameters and energy conditions for the model are derived and examined. The results show that the model is in good agreement with observations, and can serve as a valuable starting point for analyzing FLRW models in the $f(Q,T)$ theory of gravity.

astro-ph.CO↗