arXiv subjects

Ahmad Al-Badawi

Publications and source records attributed to Ahmad Al-Badawi.

At least 19 recordsLinked to original sources

arXiv2026

Horizon Structure and Geodesic Properties of Simpson-Visser Black Holes in Einstein-Euler-Heisenberg Theory

We investigate a regularized charged black hole (BH) spacetime constructed by applying the Simpson-Visser (SV) prescription to a BH in Einstein-Euler-Heisenberg (EEH) theory. The resulting Simpson-Visser Einstein-Euler-Heisenberg (SV-EEH) geometry incorporates nonlinear electromagnetic corrections through the parameter $(a)$ and the SV regularization through the length scale $(b)$. By varying these parameters, spacetime provides a smooth interpolation between a regular BH, a one-way wormhole, and a traversable wormhole configuration. Introducing the effective areal radius $(R=\sqrt{r^{2}+b^{2}})$, we analyze the horizon structure and derive the conditions for degenerate and extremal configurations. Furthermore, we examine the null and timelike geodesic structures, computing the photon sphere radius, the BH shadow size, and the innermost stable circular orbit (ISCO). Our results demonstrate how nonlinear electrodynamics and SV regularization jointly modify the causal and geodesic structure of charged BHs while preserving the appropriate Reissner-Nordström and SV limits.

gr-qc↗

arXiv2026

Particle Dynamics and Thermodynamics of a Charged-Like Hairy Black Hole in Extended Gravitational Decoupling

This work focuses on the analysis of particle dynamics and the thermodynamic properties associated with a particular branch of hairy black hole solutions. These solutions are obtained by using extended geometric deformation gravitational decoupling on the seed solution of the Schwarzschild solution. This resulting geometry satisfies the dominant energy condition and the condition $Q^{2}=2χ\ell M$. We analyze the motion of massive particles and photons in this geometry and the thermodynamics of this solution. In particular, for massless particles, we study the effective potential and determine the radii of the photon sphere and the shadow of the black hole. For massive particles, we calculate the specific energy and angular momentum of circular orbits, the ISCO, the radiative efficiency of an accretion disk, and representative particle trajectories. Finally, we investigate the thermodynamic properties of this hairy black hole geometry, including the Hawking temperature, the Bekenstein-Hawking entropy, and the heat capacity in the fixed-$(Q,\ell)$ ensemble.

gr-qc↗

arXiv2026

Modified Black Hole Physics in Quantum Gravity with Quintessence and Topological Defects

We study a static, spherically symmetric black hole (BH) of the quantum Oppenheimer-Snyder (QOS) type surrounded by a quintessence field (QF) and a cloud of strings (CS). Because the line element has the mass-function form, the Einstein tensor is linear in the mass function, and the three contributions enter the effective field equations additively with no cross terms. For the state parameter $w=-2/3$ adopted throughout, the geometry is not asymptotically flat. The horizon condition is a quintic in $r$ whose real positive roots are an inner horizon, the BH horizon, and an outer quintessence horizon, and the static region is bounded by the last two. Working inside that region, we obtain the photon sphere, the critical impact parameter, and the shadow radius seen by a static observer at finite radius, together with null and timelike geodesics, the Lyapunov exponent of circular null orbits, the orbital speed, and the geodetic precession frequency. For scalar, electromagnetic (EM), and Dirac test fields we derive the master equations and establish mode stability, using an S-deformation for the scalar sector and the supersymmetric factorization of the Dirac pair. The associated quasinormal mode (QNM) frequencies are computed at third-order WKB order and benchmarked against Schwarzschild. Damping weakens as the CS parameter and the QF normalization grow, whereas the loop quantum gravity (LQG) deformation acts only weakly. On the thermodynamic side we fix the surface-gravity prescription appropriate to a spacetime with two Killing horizons. The Hawking temperature stays non-negative over the whole admissible branch and vanishes at the degenerate configuration in which the BH horizon merges with the quintessence horizon, so no negative-temperature phase arises. Specific heat and Gibbs free energy are re-examined on that branch.

gr-qc↗

arXiv2026

Geodesics and thermodynamics of a $κ$-deformed anti-de Sitter black hole surrounded by a quintessence field

We investigate the geodesic structure and thermodynamics of a $κ$-deformed Schwarzschild-anti-de Sitter black hole in a Kiselev quintessence field, where dynamics are governed by a mass-dependent lapse deformation. This term produces an inner Cauchy horizon without requiring charge or spin, yet it fails to resolve the central singularity; instead, the Kretschmann scalar diverges more strongly as $r^{-10}$. Because the deformation amplitude couples to the mass, the standard Bekenstein-Hawking area law violates the first law of thermodynamics. We resolve this by either deriving a modified entropy or rescaling the mass, both of which restore the first law and yield a consistent Smarr relation. Optically, an increasing deformation parameter shrinks both the photon sphere and the critical impact parameter. We also derive a closed-form Joule-Thomson coefficient, revealing that the $κ$-deformation triggers an inversion curve a feature absent in standard neutral SAdS. Notably, this occurs without generating a van der Waals critical point, demonstrating that Joule-Thomson inversion and van der Waals criticality can be cleanly decoupled. Finally, the deformation suppresses peak Hawking emission by a factor of roughly four and increases flux sparsity, an effect driven almost entirely by a drop in temperature rather than changes to the black hole shadow.

gr-qc↗

arXiv2026

An exact dyonic black hole at the integrable locus of quadratic nonlinear electrodynamics

We obtain an exact dyonic black-hole solution in quadratic nonlinear electrodynamics defined by $-F+aF^{2}+bG^{2}$ on the special locus $b=a/2$. At this locus, the radial dependence in the electric constitutive relation cancels and the magnetic charge decouples, allowing the field equations to be integrated exactly. Using the field strength as the independent variable, we construct the solution in parametric closed form, with the radial quadrature expressed through Gauss hypergeometric functions and the cosmological constant retained. The solution recovers dyonic Reissner--Nordström--(anti-)de Sitter in the Maxwell limit, the known magnetic solution for vanishing electric charge, and the Euler--Heisenberg electric branch for vanishing magnetic charge. Its perturbative expansion agrees with the known dyonic result at first order and extends it to all orders. We find a three-horizon window requiring both electric and magnetic charges, while the corresponding Smarr integral is also expressed in closed hypergeometric form. The energy density and pressures are obtained analytically, showing that the electric charge enlarges the region satisfying the dominant energy condition relative to the purely magnetic case. Three distinct central curvature behaviors are identified, including a tuned self-energy singularity. We further develop the extended thermodynamics, treating the nonlinear coupling and pressure as thermodynamic variables, and find that the critical ratio decreases below the Maxwell value $3/8$ and disappears above a threshold coupling. Finally, birefringent photon propagation produces a split shadow doublet with a splitting of about $0.5\%$, whereas the geometric light ring and scalar ringdown are nearly insensitive to the nonlinear coupling, indicating that the main observable imprint of the nonlinearity lies in polarization-dependent photon propagation.

gr-qc↗

arXiv2026

Particle dynamics and quasi-periodic oscillations of a Reissner--Nordström-like black hole in Kalb--Ramond gravity under an external magnetic test field

We investigate the dynamics of charged test particles and quasi-periodic oscillations around a Reissner--Nordström-like black hole in Kalb--Ramond (KR) gravity in the presence of an external magnetic test field. The KR background introduces a Lorentz-violating parameter $\ell$, which modifies the spacetime geometry, horizon structure, circular orbits, and characteristic frequencies of particle motion. In contrast to the standard Wald-type prescription, the magnetic-field configuration is constructed from the source-free Maxwell equation on the charged KR background, allowing the magnetic profile to be consistently adapted to the modified geometry. We derive the equations of motion, the effective potential, the conditions for circular orbits, and the orbital and radial epicyclic frequencies of charged particles. The results show that the black-hole charge $Q/M$, the KR parameter $\ell$, the specific particle charge $ε$, and the magnetic coupling $β=bM$ jointly affect the innermost stable circular orbit (ISCO) and the quasi-periodic oscillation (QPO) frequencies. We then apply the obtained frequencies to the relativistic precession model, where the upper QPO frequency is identified with the orbital frequency and the lower one with the periastron-precession frequency. Using the observed twin-peak QPO data of GRO J1655--40, XTE J1550--564, and M82 X-1, we perform a Markov chain Monte Carlo analysis to constrain the model parameters. The obtained posterior constraints indicate that the charged KR black-hole model with an external magnetic field can consistently reproduce the observed QPO pairs within the adopted parameter ranges. These findings suggest that QPO observations may serve as a useful phenomenological tool for probing Lorentz-violating black-hole geometries and electromagnetic effects in strong-gravity environments.

gr-qc↗

arXiv2026

Renormalization-group improved Schwarzschild black hole: shadow, ringdown, and strong cosmic censorship

A renormalization-group (RG) improved Schwarzschild-like black hole (BH) is studied here, with a lapse that interpolates between a classical Schwarzschild exterior and a quantum-smoothed interior set by a cutoff scale $ξ$ and an interpolation parameter $γ$. We work out the horizon structure together with the photon sphere and shadow radius $R_{\mathrm{sh}}$, set up the scalar, electromagnetic, and Dirac Regge-Wheeler-Zerilli problems in a single treatment, and compute the fundamental and overtone quasinormal modes by sixth-order WKB, cross-checked against time-domain ringdown. For $ξ>0$ and $γ>0$ the geometry is regular, with a de Sitter core. Strong Cosmic Censorship (SCC) is examined at the inner Cauchy horizon, which the improved geometry generates without charge or rotation. The quasinormal spectral gap $β=|\mathrm{Im}\,ω|/κ_-$ stays multipole-independent at the $6\%$ level and follows $β\simeqλ_{L}/(2κ_{-})$. It remains below the de Sitter Christodoulou bound across the parameter range, and the asymptotically flat late-time tail places the geometry in the SCC-respecting class. A thermodynamic analysis identifies a Davies-type phase transition of the outer horizon, with the Schwarzschild $T_{H}\propto 1/r_{+}$ decay replaced by a bell-curve profile peaking at $T_{H}^{\max}\simeq 0.062$. A scan of the $(ξ,γ)$ plane gathers the joint behavior of the shadow, the scalar barrier, the SCC ratio, and $T_H$. Set against Bardeen, Hayward, and Bonanno-Reuter BHs at matched perturbation scale, the improved Schwarzschild BH is the most Schwarzschild-like of the regular-BH family, its static shadow radius degenerate with Hayward and Bonanno-Reuter at the percent level. The closing analysis takes up the sparsity of the Hawking flux and the energy-emission rate, both tied to the outer-horizon surface gravity through a single auxiliary function.

gr-qc↗

arXiv2026

MCMC Constraints on Dyonic Kalb-Ramond Black Holes with a Cloud of Strings from Twin-Peak QPOs and EHT Shadows

We study a dyonic black hole in a Lorentz-violating gravity that carries a background Kalb--Ramond field and is pierced by a cloud of strings. The resulting metric reduces to the recent Lin--Liu--Liu solution when the string density~$ξ$ is switched off, and to the Duan and Yang solutions in further degenerate limits. We work out the timelike circular geodesics and read off the quasi-periodic oscillation (QPO) frequencies $ν_ϕ$, $ν_r$ and $ν_θ$ within both the relativistic-precession and epicyclic-resonance models. We then map these frequencies onto the observed twin-peak signals of XTE~J1550$-$564, GRO~J1655$-$40 and GRS~1915$+$105, and place constraints on $(\ell, ξ)$ from a Markov chain Monte Carlo (MCMC) fit. We extract the full thermodynamic dictionary, first law and Smarr relation included, and follow the heat capacity, free energy and sparsity of Hawking radiation through their dependence on the four parameters $(M, Q, p, \ell, ξ)$. Finally, we compute the spectral energy emission rate and look at the photon-sphere and shadow radii in the presence of the cosmic string. The Lorentz-violating coupling $\ell$, the magnetic charge $p$, and the string density $ξ$ all leave distinct fingerprints on the dynamical, thermodynamic and radiative observables, with $ξ$ exerting the strongest pull on the ISCO, the shadow size and the sparsity of Hawking emission

gr-qc↗

arXiv2026

Are Petrov type-N and D spacetimes admitting CTCs valid in $f(R,\mathcal{L}_m,Φ,X)$ gravity?

We ask whether two classical time-machine geometries, the Ori (2005) compact-vacuum-core metric and the Ahmed (2018) four-dimensional generalisation of Misner space, remain admissible exact solutions when the gravitational sector is enlarged to the recently proposed $f(R,\mathcal{L}_{m},Φ,X)$ class, an extension of $f(R,\mathcal{L}_{m})$ that couples curvature, the matter Lagrangian density, a scalar field $Φ$, and its kinetic invariant $X = g^{μν}\nabla_μΦ\nabla_νΦ$. Working with the explicit model $f = R + \mathcal{L}_{m} + (λ/2)\,X$ and a vanishing scalar potential, we compute the curvature invariants, the modified field equations, and the effective stress-energy components produced by the harmonic scalar profile $Φ(x,y) = a(x^{2}-y^{2})/2$ in both backgrounds. The Ricci scalar vanishes for the Ori metric and obeys $R = e^{f}(f_{,xx}+f_{,yy})$ for the Ahmed metric; the kinetic invariant takes the explicit forms $X = a^{2}(x^{2}+y^{2})$ and $X = a^{2}e^{f}(x^{2}+y^{2})$, respectively. Both metrics solve the field equations of the modified theory with anisotropic matter sources, and the chronology-violating regions $g_{zz}<0$ (Ori) and $g_{ψψ}<0$ (Ahmed) survive the modification. Energy-density profiles measured by a closed-timelike-curve observer match those measured by a static observer outside the chronology horizon, so the additional scalar degree of freedom in $f(R,\mathcal{L}_{m},Φ,X)$ gravity does not enforce a chronology-protection mechanism in either background. The conclusion mirrors the parallel result for the Li time-machine and supplies a consistency test for scalar-extended modified gravity in non-globally-hyperbolic settings.

gr-qc↗

arXiv2026

Transfer observables of rotating acoustic black holes from ray tracing: shadow centroid, redshift asymmetry and flux imbalance

We construct an impact-parameter-resolved transfer framework for null acoustic rays in the rotating draining-bathtub spacetime. The formalism separates the source-independent ray geometry from the source and detector model by keeping explicit the acoustic redshift, transfer convention, emissivity, emitter velocity field, and source-to-screen mapping. The geometric capture interval provides two clean observables: a shadow centroid that shifts linearly with circulation and a shadow width that grows monotonically with circulation. Observable profiles are obtained from direct ray-source intersections, finite source width or extended-disk integration, detector convolution, and convergence checks, rather than from an approximate semi-analytic ring map. The transfer calculation shows that rotation produces a left-right redshift tilt and a branch-dependent flux imbalance, while the total flux alone remains a degenerate circulation diagnostic. The most useful diagnostics are differential quantities: the shadow centroid, branch-integrated flux asymmetry, peak asymmetry, left-right redshift asymmetry, and global redshift contrast. We also discuss how these observables respond to the transfer convention, intrinsic azimuthal emissivity, the choice of left-right split, finite resolution, and physical limitations such as dispersion, viscosity, and finite-depth corrections.

gr-qc↗

arXiv2026

Particle Dynamics, Shadow and Hawking Sparsity of a Kalb-Ramond Black Hole Coupled to Nonlinear Electrodynamics

We study the timelike and null geodesic structure of a static, spherically symmetric black hole sourced by a Kalb--Ramond (KR) field coupled to nonlinear electrodynamics (NED). The geometry is characterized by the mass $M$, the magnetic monopole charge $q$, and the Lorentz-violating parameters $(γ,λ)$. Closed-form expressions are derived for the effective potential, as well as the specific energy and angular momentum of massive particles on circular orbits. We further analyze the photon sphere, black hole shadow, and the Lyapunov exponent associated with unstable null circular geodesics. The latter determines the eikonal quasinormal-mode frequencies through $ω_{\rm eik}=(\ell+1/2)\,Ω_c-i(n+1/2)\,|λ_L|$. The shadow radius is compared with the Event Horizon Telescope (EHT) observations of M87$^\ast$ and Sgr~A$^\ast$, allowing us to identify the viable region in the $(q,γ)$ parameter space. Finally, we compute the Hawking temperature, horizon area, and the Gray--Visser sparsity parameter. We demonstrate that the combined effects of the KR field and magnetic monopole charge increase the sparsity parameter from the Schwarzschild value $16π^3 \simeq 496$ to nearly $1.7\times10^3$. This indicates a significantly sparser Hawking cascade compared to the Schwarzschild case, while the photon ring remains consistent with the EHT $1σ$ observational bounds across most of the physically allowed parameter range.

gr-qc↗

arXiv2026

Thermodynamics and optical aspects of ModMax black holes in higher order curvature gravity with quintessence dark energy

In this work, we derive an exact black hole solution in higher-order curvature gravity by coupling an electromagnetic sector formulated within the ModMax framework to a quintessence dark energy component. Focusing on purely electrically charged configurations, we analyze the thermodynamic and geothermodynamic properties of the solution to investigate its stability and phase structure. Within this sector, the ModMax theory effectively reduces Maxwell electrodynamics up to a rescaling of the electric charge, and thus the obtained solution corresponds to a consistent subset of the broader nonlinear theory. Using thermodynamic geometry, we examine microscopic interactions and phase transitions, showing that divergences in the thermodynamic curvature coincide with the vanishing of the heat capacity, confirming the consistency of the phase structure. We further explore the optical properties of the black hole by studying null geodesics and determining the photon sphere and the corresponding shadow radius for different values of the quintessence state parameter $ω$. Exact analytical expressions for the photon-sphere radius are derived, revealing that higher-order curvature corrections and quintessence significantly enhance the shadow size, whereas the electric charge has the opposite effect. Notably, quintessence is found to have a more pronounced impact on the shadow than the charge. These results highlight that dark energy and higher-order curvature corrections can yield potentially observable signatures in black hole shadows.

gr-qc↗

arXiv2026

Astrophysical signatures of Kerr-Bertotti-Robinson black holes in a cloud of strings: ISCO, microquasar QPOs, and Bondi-Hoyle-Lyttleton accretion

We study test-particle dynamics in the equatorial plane of a Kerr-Bertotti-Robinson black hole (BH) immersed in a cloud of strings (CS), with mass M , rotation a, magnetic parameter B, and string parameter α. Using the Hamilton formalism we recover the effective potential Ueff and the conditions for circular motion, and we compute the specific energy E and specific angular momentum L together with the radial, vertical, and azimuthal epicyclic frequencies νr , νθ , νϕ. Going beyond the analytic setup, we provide the first numerical mapping of the innermost stable circular orbit (ISCO) for this background and tabulate rISCO, EISCO, LISCO, and the accretion efficiency η = 1 - EISCO for both co- and counter-rotating motion across a wide (a, B, α) grid. The CS parameter pushes the ISCO outward and raises η from 0.057 in Schwarzschild to above 0.25 for α = 0.30 at a = 0.9. We then connect the model with observed twin-peak high-frequency quasi-periodic oscillations (QPOs) in three microquasars (GRO J1655-40, XTE J1550-564, GRS 1915+105) using the relativistic-precession (RP) model and find \{chi}^2-minimum fits with α < 0.13. A general-relativistic hydrodynamical (GRH) study of Bondi-Hoyle-Lyttleton (BHL) accretion completes the picture: the CS contribution sustains shock-cone instabilities, redistributes power-spectral-density (PSD) peaks, and produces low-frequency QPO-like components that distinguish KBR+CS from pure Kerr or KBR.

astro-ph.HE↗

arXiv2026

Hawking Temperature, Sparsity and Energy Emission Rate of Regular Black Holes Supported by Primordial Dark Matter

In this paper, we investigate the thermodynamic and radiative properties of a regular black hole sourced by primordial dark matter (PDM), modeled effectively through a Dirac--Born--Infeld (DBI) scalar field. We compute the Hawking temperature, the entropy obtained from the first law at fixed PDM scale, the specific heat capacity, the sparsity parameter of the Hawking flux, and the spectral energy emission rate. Particular attention is devoted to the role played by the regularity scale parameter $α$ and to the recovery of the Schwarzschild limit. Using the normalization in which the integration constant $M$ is the ADM mass and $f(r)=1-2M/r+\mathcal{O}(r^{-3})$, we find that the PDM scale suppresses the Hawking temperature and the spectral energy emission rate relative to the Schwarzschild case. The fixed-$α$ heat capacity remains negative along the physical branch, indicating the persistence of local thermodynamic instability in the canonical ensemble. Moreover, within the effective-area prescription adopted here, the geometrical sparsity parameter receives a negative leading correction in the perturbative regime $α\ll 2M$, implying a slight reduction of the intermittency of the Hawking flux. We also distinguish between the near-horizon geometrical estimate and the shadow-based high-energy absorption cross-section used in the emission rate.

gr-qc↗

arXiv2026

Astrophysical Signatures of Einstein-Skyrme Anti-de Sitter Black Holes: Epicyclic Frequencies and QPO Constraints

We study the geodesic motion and epicyclic oscillations of massive test particles around a static, spherically symmetric black hole (BH) solution of the Einstein--Skyrme (ES) theory in Anti-de Sitter (AdS) spacetime. The lapse function of this BH depends on the Skyrme coupling $η$, a charge-like parameter $Q$ inherited from the Skyrme term, and the cosmological constant $Λ<0$. We first map out the horizon structure and identify three regimes-non-extremal BH (NEBH), extremal BH (EBH), and naked BH (NBH)-showing that the NEBH $\to$ EBH $\to$ NBH transition is governed by $Q$ rather than $η$, which enters $f(r)$ only as a constant shift. We then derive the effective potential (EP), locate the innermost stable circular orbit (ISCO), and compute the radiative efficiency, finding that $\mathcal{E}_{\rm ISCO}>1$ in AdS renders the standard Novikov-Thorne formula negative. The corrected radial epicyclic frequency $Ω_r$ reveals a distinctive AdS signature: $ν_r$ grows at large $r$ and overtakes the orbital frequency $ν_ϕ$, causing the periastron precession frequency $ν_p = ν_φ- ν_r$ to change sign-a feature absent in asymptotically flat geometries. Adopting the relativistic precession (RP) model for quasi-periodic oscillations (QPOs), we perform a Markov chain Monte Carlo (MCMC) analysis using twin-peak QPO data from XTE~J1550-564, GRO~J1655-40, Sgr~A$^*$, and M82~X-1. The posteriors converge to $Q\approx 0.6$ across all sources, with orbital radii near $r\approx 4.2\,M$ and masses consistent with independent estimates, demonstrating that the ES-AdS BH accommodates the observed frequency pairs within physically motivated parameter ranges.

gr-qc↗

arXiv2026

Spin-($0$, $1$, $\frac{1}{2}$) Field Perturbations, Quasinormal Modes, Overtones, Greybody Factors and Strong Cosmic Censorship of Einstein-Skyrme Black Holes

We carry out a multi-spin perturbation-theory study of the four-dimensional Einstein-Skyrme (ES) anti-de Sitter (AdS) black hole (BH), whose lapse $f(r)=1-8πK-2M/r+4πKλ/r^{2}$ inherits two couplings from the hadronic model -- the pion combination $K=F_π^{2}/4$ and the Skyrme coupling $e$ -- with $Kλ=1/e^{2}$ pinned by the theory rather than being a free integration constant. After deriving the Klein-Gordon, Maxwell and Dirac effective potentials on this background, we compute the quasinormal modes (QNMs) with the sixth-order WKB formula and cross-check them against the thirteenth-order Padé-improved expansion and the eikonal limit set by the unstable photon sphere. The first overtone $(n=1)$ of the scalar and electromagnetic channels reveals a mild Konoplya-Zhidenko anomaly: the ratio $|\mathrm{Im}\,ω_{1}|/|\mathrm{Im}\,ω_{0}|$ drifts monotonically from $2.42$ to $2.54$, sitting noticeably below the Schwarzschild value near $3$. The dominant scalar mode is independently reproduced to better than $0.2\%$ by a time-domain Prony fit. Greybody factors for all three spins follow the ordering $T_{\rm EM}<T_{\rm scalar}<T_{\rm Dirac}$. Testing strong cosmic censorship at the Cauchy horizon, we find the Christodoulou parameter $β\lesssim 4\times 10^{-3}$ across the admissible $(K,e)$ window -- more than two orders of magnitude below the threshold $1/2$ -- with the margin protected by the theory itself.

gr-qc↗

arXiv2026

Shadow, Sparsity of Radiation and Energy Emission Rate in Skyrmion Black Holes

We examine several observable optical properties of a Skyrmion black hole (BH), focusing on the photon sphere, BH shadow, and photon trajectories. The Skyrme term, along with other geometric parameters of the spacetime, determines the photon sphere location and shapes the resulting BH shadow. Parameter variations produce observable departures from standard BH geometries, offering potential signatures of nonlinear field effects. We also analyze the sparsity of Hawking radiation and the associated energy emission spectra, showing how these quantities respond to the Skyrme coupling and background parameters. Our findings illuminate the connection between nonlinear field contributions and BH optics, with implications for observational and theoretical studies of modified gravity scenarios.

gr-qc↗

arXiv2026

Plummer Dark Matter Black Hole with Topological Defects: Shadow, Greybody Factors, Quasinormal Modes, and Thermodynamics

We construct a static, spherically symmetric black hole (BH) solution embedded in a cored Plummer dark matter (DM) halo and a Letelier cloud of strings (CoS). Starting from the Plummer-Schwarzschild metric of Senjaya et al.~\cite{Senjaya2026}, we incorporate the string-cloud tension parameter $α$ into the lapse function, obtaining $A(r) = h_{\rm Plummer}(r) - α$. The resulting spacetime admits a single, non-degenerate event horizon (EH) for $α< 1$ and a naked singularity for $α\ge 1$. We determine the photon sphere (PS) and BH shadow radii, compute the weak deflection angle via the Gauss-Bonnet theorem (GBT), and analyze the innermost stable circular orbit (ISCO). Scalar perturbations are studied through the effective potential, greybody factor (GF) bounds obtained from the Boonserm-Visser method, the Hawking emission spectrum, and quasinormal mode (QNM) frequencies computed with the WKB approximation. The thermodynamic analysis covers the Hawking temperature, Bekenstein-Hawking entropy, heat capacity, and Gibbs free energy; the heat capacity is found to be strictly negative for all parameter values, confirming the absence of any Davies-type phase transition. A consistent hierarchy emerges across all six analyses: the CoS tension $α$ governs the leading-order modifications to every observable, while the Plummer halo density $ρ_0$ provides a subdominant, additive correction.

gr-qc↗