arXiv subjects

Zheng-Wen Long

Publications and source records attributed to Zheng-Wen Long.

At least 19 recordsLinked to original sources

arXiv2026

Radiative properties and optical appearance of a thin accretion disk around a charged-PFDM black hole

Accretion onto magnetically charged black holes in a perfect fluid dark matter (PFDM) background opens a new window for testing strong-field gravity. This paper investigates the radiative properties and optical appearance of a thin accretion disk surrounding a charged-PFDM black hole. We numerically compute the radiative energy flux, temperature distribution, and radiative efficiency, and employ a ray-tracing method to construct the direct images, secondary images, redshift distribution, and observed flux. By comparing with the Schwarzschild and pure PFDM cases, we find that the thin-disk efficiency of the charged-PFDM black hole lies between the two, with the magnetic charge partially counteracting the dark-matter-induced efficiency enhancement; for M87*, the efficiency is estimated to be 7\%--8\%. The optical appearance is predominantly governed by the PFDM parameter, while the magnetic charge plays only a marginal role. Larger inclination angles give rise to stronger Doppler asymmetry, producing the characteristic ``hat-like'' shape. These results provide falsifiable predictions for future high-resolution observations, such as those by ngEHT, to distinguish dark-matter environments from magnetic-charge effects.

astro-ph.HE↗

arXiv2026

Thermodynamic topological classification of magnetically charged slowly rotating Kerr black holes in nonlinear electrodynamics with a cosmological constant

In this work, we investigate the thermodynamic topological classification of slowly rotating Kerr black holes with magnetic charge in nonlinear electrodynamics (NLED) using a reduced grand-canonical off-shell prescription. By constructing the generalized off-shell free energy and the associated topological vector field, we determine the local winding numbers and the global topological charge of the NLED-Kerr black hole in both de Sitter (dS) and anti-de Sitter (AdS) spacetimes. The inverse-temperature curve starts from a finite nonzero value at the lower radial endpoint and diverges at large horizon radius. Together with the single zero of winding number $w=-1$, this behavior identifies the black hole as a realization of the predicted $\overline{W}^{1-}$ subclass, with global topological number $W=-1$ and a single unstable branch. The classification remains unchanged over the sampled rotation, NLED, and magnetic-charge parameters. Within the same prescription, comparison with the two-branch $W^{0-}$ Kerr-AdS result associates the NLED effective mass function with the changed endpoint behavior and the absence of a stable large-black-hole branch. Thus, the physical novelty is an explicit rotating NLED realization of the predicted $\overline{W}^{1-}$ subclass for both signs of the cosmological constant.

gr-qc↗

arXiv2026

Echoes of a hairy black hole from gravitational decoupling

We study axial gravitational perturbations of a hairy black hole constructed within the framework of gravitational decoupling and investigate the geometric origin of echo-like late-time signals in this spacetime. We derive the odd-parity master equation and the corresponding effective potential, and compute the quasinormal mode spectrum using frequency-domain and time-domain methods. We show that the axial potential develops a double-peak structure that supports a trapping cavity and gives rise to echo-like waveforms. The representative double-peak configurations also exhibit an unstable--stable--unstable light-ring structure, which provides the null-geodesic counterpart of the trapping cavity in the eikonal limit. Therefore, the echoes are not produced by an artificially imposed near-horizon condition, but instead emerge dynamically from the geometric structure of the effective potential. Our results provide a useful framework for probing black hole hair through gravitational-wave ringdown and for exploring possible observational departures from the standard no-hair paradigm.

gr-qc↗

arXiv2026

Quasinormal Modes, Partial Transmission Probabilities, and Hod's Conjecture of Charged Black Holes in Perfect Fluid Dark Matter within Kalb-Ramond Gravity

Within the Kalb-Ramond field-induced Lorentz-violating gravity, we investigate the perturbation dynamics and quasinormal mode (QNM) spectra of a charged black hole immersed in perfect fluid dark matter. The background spacetime is characterized by the Lorentz-violating parameter tau, the electric charge Q/M, and the dark matter parameter lambda/M. Owing to the non-zero vacuum expectation value of the KR field, the metric function approaches 1/(1-tau) at infinity instead of 1, rendering the spacetime non-asymptotically flat. Under the test-field approximation, the equations of motion for three types of perturbations (scalar, electromagnetic, and axial gravitational) are reduced to Schrodinger-type radial equations with single-peak effective potentials. The QNM frequencies are cross-validated using the sixth-order WKB method and the time-domain Prony method, while the partial transmission probabilities are computed within the WKB scattering framework. Parameter scans show that tau exerts the strongest influence on the QNM spectrum, followed by lambda/M, with Q/M having the weakest effect; the same ordering holds for the partial transmission probabilities. Under the same parameters, the QNM frequencies of the three perturbations follow the order scalar > electromagnetic > gravitational, whereas the transmission probabilities exhibit the reverse order, reflecting the different impact of the effective potential height on the oscillation frequency and on the transmission probability. The Hod conjecture |Im(omega)| <= pi T_H holds throughout the parameter range examined.

gr-qc↗

arXiv2026

Gravito-Electromagnetic perturbation of higher derivative corrected Kerr-Newman black hole

We study linear gravito-electromagnetic perturbations of a slowly rotating 4-derivative corrected Kerr-Newman (KN) black hole (BH), using a perturbative approach beyond the KN geometry up to first order in angular momentum, first order in the higher-derivative parameters ci, i = 1,2...8, and 14th order in the BH electric charge. We derive the corrected coupled radial master equations for both axial and polar perturbation sectors. We extend the asymptotic iteration method (AIM) to apply to coupled second-order ordinary differential equations (ODEs) and employ it to compute the quasinormal frequencies (QNFs) of the system.Our results show pronounced isospectrality breakings between the two parity sectors, induced by c6,c7 and c8,particularly for high charge BH.This indicate the equations for the two parity sectors lose the transformation symmetry that relates them in the KN case.The very tiny frequency shifts induced by c4 support the interpretation that this parameter represents a redundant degree of freedom in the effective field theory.Finally, we parameterize the QNFs via a analytical fitting procedure for broader applicability.

gr-qc↗

arXiv2026

Multiscale probing of a Hernquist-type environmental black hole spacetime with the Sgr A* shadow and S2 orbital dynamics

The supermassive black hole Sgr A* at the Galactic center provides a unique opportunity to probe the distribution of environmental matter around black holes. In this work, we adopt the Hernquist-type environmental black hole spacetime, a non-vacuum exact solution of the Einstein field equations, as its gravitational model to describe the joint gravitational field of the black hole and its surrounding matter, with environmental effects characterized by the dimensionless compactness $C$ and the characteristic scale $α$. We combine black hole shadow data with two sets of S2 star data provided by Do et al. and Gillessen et al., and constrain the model parameters using the Markov chain Monte Carlo method. At the 95\% credible upper limit, the shadow-only data constrain $C < 1.498\times10^{-1}$.but provide no effective constraint on $α$. The two S2 datasets yield $C<5.239\times10^{-5}$ and $C<1.303\times10^{-4}$, respectively, with $α$ exhibiting a bimodal structure in both cases. After combining the shadow and S2 star data, the $C$ upper limits are tightened to $C<3.760\times10^{-5}$ and $C<1.073\times10^{-4}$, respectively. These results indicate that current observations rule out highly compact configurations of the environmental halo, while the obtained constraints are consistent with the typical compactness range of matter halos. However, $α$ still exhibits a significant bimodal degeneracy, indicating that current observations are insufficient to uniquely determine the radial distribution of the environmental halo. Future observations of multiple stellar orbits may provide further insights into the radial structure of the environmental halo.

gr-qc↗

arXiv2026

Quasinormal modes of Kerr-like black bounce spacetime

We investigate the quasinormal mode (QNM) spectrum of a Kerr-like black-bounce spacetime under massive scalar-field perturbations. Starting from the Kerr-like deformation of the Simpson--Visser black-bounce geometry, we derive the corresponding radial and angular equations and obtain the effective potential governing scalar perturbations. The QNM frequencies are computed by means of the Pöschl--Teller potential approximation and the semi-analytic WKB method (up to sixth order), and we demonstrate reasonable agreement between these two approaches. We then analyze in detail how the QNM spectrum depends on the spin parameter $a$, the bounce parameter $p$ that interpolates between black-hole and wormhole geometries, and the scalar-field mass $μ$. Our results show that increasing the spin parameter $a$ raises the oscillation frequency, while increasing the bounce parameter $p$ lowers it, and in both cases the damping rate decreases. Moreover, the mass of the scalar field has a non-negligible impact on the ringdown spectrum. These features suggest that rotating black-bounce geometries may leave distinct imprints in the ringdown phase of gravitational-wave signals, and motivate future studies of echoes and parameter estimation in the context of present and upcoming detectors.

gr-qc↗

arXiv2026

Novel topological subclass in Bardeen-AdS-class black holes

Based on the $ϕ$-mapping topological current theory, we systematically investigate the thermodynamic topology of regular Bardeen-AdS-class black holes coupled to nonlinear electrodynamics, a class of singularity-free geometries whose topological classification remains underexplored. We implement numerical calculations at two typical AdS radii $L=1$ and $L=15$. Within the fundamental $W^{0-}$ topological family, we identify a novel inner secondary subclass $\widetilde{W}^{0-}$. This result only refines and enriches the internal branch structure of the $W^{0-}$ family under the established classification scheme of five topological classes and four topological subclasses for black hole thermodynamics. This new subclass has a vanishing global topological charge $W=0$ with an inner-outer horizon winding-number signature $[-,+]$. Unlike standard $W^{0-}$ solutions that realize topological extension via embedded $(+,-)$ winding pairs, $\widetilde{W}^{0-}$ arises from attaching an extra stable branch to the end of the base solution sequence. Two critical coupling parameters $\hat{m}_{01}$ and $\hat{m}_{02}$ divide the full parameter space into distinct topological phases: Type I black holes with $m_0\ge\hat{m}_{01}$ and Type II solutions with $\hat{m}_{02}<m_0<\hat{m}_{01}$ belong to $\widetilde{W}^{0-}$, while the parameter region $0<m_0\le\hat{m}_{02}$ corresponds to the conventional $W^{0-}$ topology. Our numerical results verify the self-consistency of the thermodynamic topological formalism when applied to singularity-free regular black holes, refine the topological discrimination criteria tailored to nonlinear-electrodynamics regular black holes, and provide theoretical references for subsequent topological investigations of higher-dimensional rotating regular black holes under the same formalism.

gr-qc↗

arXiv2026

Universal thermodynamic topological classes of the charged dRGT black string

In this study, we explore universal thermodynamic topological classes of charged dRGT black string within both the canonical ensemble and grand canonical ensemble frameworks, and further analyze its asymptotic behavior under limiting parameter regimes. We demonstrate that, while the outermost large black string branch remains thermodynamically stable in both ensembles, the innermost small black string branch exhibits distinctly different stability properties: it is stable in the canonical ensemble but becomes thermodynamically unstable in the grand canonical ensemble, corresponding to the $W^{1+}$ and $W^{0-}$ topological categories, respectively. Furthermore, the local thermodynamic stability of the charged dRGT black string is investigated through the behavior of the heat capacity. These findings demonstrate that the selection of thermodynamic ensemble has a significant influence on the thermodynamic configuration of the charged dRGT black string. In the limit where gravitational effects are neglected, the charge contribution does not modify the underlying topological classification. This implies that the coupling between dRGT massive gravity and the electromagnetic sector is essential for the emergence of nontrivial thermodynamic topology. These results contribute to a deeper understanding of the black string thermodynamics and provide a novel theoretical basis for exploring the basic properties of quantum gravity.

gr-qc↗

arXiv2026

Ringdown of a black hole sourced by a Burkert-density effective anisotropic source

We construct a static, spherically symmetric black hole spacetime sourced by an effective anisotropic matter distribution whose energy density follows the cored Burkert profile. The source should be understood as a Burkert-density effective fluid, rather than as a microscopic model of pressureless collisionless dark matter. Solving the Einstein equations under this closure condition, we obtain an analytic Schwarzschild-like metric that reduces smoothly to the vacuum Schwarzschild solution when the halo contribution vanishes. We then study axial gravitational perturbations of this geometry and determine the associated quasinormal spectrum using complementary frequency-domain and time-domain methods. We find that increasing either the core radius $r_0$ or the central density $ρ_0$ shifts the ringdown toward lower frequency and weaker damping, with the effect of $r_0$ being more pronounced. The close agreement among the numerical extractions supports the reliability of the results. Our analysis provides a useful benchmark for assessing how a cored Burkert-type effective environment can modify black hole ringdown.

gr-qc↗

arXiv2026

Universal Thermodynamic Topological Classes of BTZ Black Holes in Einstein and F(R) Gravity

In this paper, we systematically study three classes of three-dimensional Bañados-Teitelboim-Zanelli (BTZ) black holes based on different gravitational frameworks and matter field structures: the Einstein-Maxwell BTZ, the F(R)-Maxwell BTZ, and the F(R)-phantom BTZ.Within the canonical and grand canonical ensemble frameworks, we construct the generalized free energy of these black hole systems and systematically analyze the asymptotic behavior of Hawking thermodynamics.The results indicate that both gravitational modifications and matter fields significantly influence black hole topology: the F(R) gravitational modification alters the intrinsic topological class of the black hole compared to the BTZ black hole under Einsteinian gravity, while different matter fields further modulate the topological classification results. Furthermore, by comparing the two types of ensembles, we find significant differences in black hole topological classes, and these differences are correlated with the gravitational framework and matter fields. In summary, the gravitational framework, matter fields, and ensemble selection are key factors governing the topological classification of black holes; all identified topological categories belong to the existing three-dimensional spacetime topological classification system, highlighting their universality. This work deepens our understanding of the thermodynamic-topological connection in three-dimensional BTZ black holes and provides a rigorous theoretical foundation for extending such topological classifications to modified gravity theories and different matter field backgrounds.

gr-qc↗

arXiv2026

Periodic orbits and gravitational waveforms around a Schwarzschild black hole with a cloud of strings embedded in perfect fluid dark matter

In this study, we explore the dynamics of particle orbits and their corresponding gravitational wave signatures in the vicinity of a Schwarzschild black hole (BH) surrounded by a cloud of strings and embedded in a perfect fluid dark matter medium. The model is characterized by two parameters: $a$, associated with the string cloud, and $α$, representing the dark matter distribution. We systematically analyze how the marginally bound orbit (MBO) and the innermost stable circular orbit (ISCO) depend on these parameters. Our findings reveal that while both the orbital radius and angular momentum increase with increasing $a$, they decrease as $α$ increases; notably, the energy exhibits the opposite trend, decreasing with $a$ and increasing with $α$. Furthermore, we examine periodic orbits indexed by rational numbers $q$ and the gravitational waveforms they generate. The results demonstrate that an increase in the string cloud parameter $a$ induces a significant phase delay in the waveform. Specifically, waveforms with lower values of $a$ oscillate over shorter time intervals, whereas those with higher values extend to longer time scales. These distinct features, including noticeable differences in amplitude, allow the waveforms to be clearly distinguished from those in a pure Schwarzschild spacetime.

gr-qc↗

arXiv2026

Thermodynamic topology of dyonic AdS black holes with quasitopological electromagnetism in Einstein-Gauss-Bonnet gravity

In this study, we investigate the thermodynamic topology of the high-dimensional dyonic AdS black holes with quasitopological electromagnetism in the Einstein-Gauss-Bonnet background. We first examine the topological charge connected to the critical point and find that the two conventional critical points $CP_{1},CP_{2}$ of the black hole are physical critical point, and the novel critical point $CP_{3}$ that lacks the capability to minimize the Gibbs free energy ($α=0.5$). The critical points $CP_{1}$ and $CP_{2}$ are observed to occur at the maximum extreme points of temperature in the isobaric curve, while the critical point $CP_{3}$, emerges at the minimum extreme points of temperature. Furthermore, the number of phases at the novel critical point exhibits an upward trend, followed by a subsequent decline at the conventional critical points. With the increase of the coupling constant ($α= 1$), although the system has three critical points, only the conventional $CP_{1}$ is a (physical) critical point, and the conventional $CP_{2}$ serves as the phase annihilation point. This means that the coupling constant $α$ has significant impact on the phase structure. Additionally, we regard dyonic AdS black holes as a topological defect within the thermodynamic space, our findings indicate that alterations in pressure can result in the system exhibiting distinct points of generation and annihilation. However, the total topological number of black holes in different dimensions is $1$, the system shares a similar topological classification as the charged RN-AdS black holes. The discovery we have made provides a crucial component in understanding the thermodynamic topology of dyonic AdS black holes.

gr-qc↗

arXiv2026

Optical Appearance and Ringdown of Black Holes in a Kalb Ramond Field Coupled to Perfect Fluid Dark Matter

This paper investigates the optical and dynamical properties of a static spherically symmetric black hole in the presence of a Kalb--Ramond (KR) field coupled to perfect fluid dark matter (PFDM). We analyze the effects of the Lorentz-violating parameter $α$ and the dark matter parameter $λ$ on photon trajectories and their observational signatures in the strong-gravity regime. Furthermore, we study the quasinormal mode spectrum under scalar, electromagnetic, and gravitational perturbations, examining how the model parameters influence the characteristic oscillation frequencies and damping rates. In particular, the interplay between the effective potential structure and perturbative dynamics is clarified, and it is found that, within the validity of the eikonal approximation, the quasinormal modes of the black hole considered here exhibit good agreement with the properties of null geodesics. Our results show that the model parameters significantly affect both the optical appearance of the black hole and the dynamical features of the ringdown phase, providing potential observational constraints on Lorentz-violating effects and dark matter environments in strong-field regimes.

gr-qc↗

arXiv2026

Connection Between the Shadow Radius and Quasinormal Frequencies for Black Holes in STVG with Perfect Fluid Dark Matter

We investigate the connection between black hole shadow and quasinormal mode (QNM) spectra in the context of scalar-tensor-vector gravity (STVG) coupled to perfect fluid dark matter (PFDM), characterized by the MOG parameter $α$ and the dark matter intensity $λ$. Employing complementary methods -- namely the sixth-order WKB approximation, Padé resummation, and time-domain numerical integration -- we compute QNM frequencies for scalar ($s=0$), electromagnetic ($s=1$), and axial gravitational ($s=2$) perturbations. Both the real part of the QNM frequencies and the peak height of the effective potential display a consistent parametric dependence: they increase with $λ$ yet decrease with growing $α$. In the eikonal limit ($l \gg 1$), we derive an exact analytical link between the shadow radius $R_{\mathrm{sh}}$ and the QNM frequency $ω_R$. Noting that $R_{\mathrm{sh}}$ is determined by the critical impact parameter $b_c = r_{\mathrm{ph}}/\sqrt{f(r_{\mathrm{ph}})}$, while $ω_R = Ωl$ with photon angular velocity $Ω= \sqrt{f(r_{\mathrm{ph}})}/r_{\mathrm{ph}}$, we obtain the precise relation $ω_R = l / b_c$, identifying $R_{\mathrm{sh}} \equiv b_c$ for an asymptotically flat observer. This prediction is robustly validated by numerical results across all three computational approaches at large multipole numbers. Our findings reveal that the black hole shadow and gravitational ringdown are not independent phenomena, but dual observational signatures of the same underlying structure -- the unstable photon orbit -- thereby offering a unified multi-messenger framework to simultaneously constrain modified gravity and dark matter in the strong-field regime.

gr-qc↗

arXiv2026

Detecting Black hole surrounded by perfect fluid dark matter in Kalb-Ramond fields using quasinormal modes

This paper investigates the characteristics of quasinormal modes (QNMs) of static, spherically symmetric black holes under the combined influence of spontaneous Lorentz symmetry breaking (LSB) induced by the Kalb-Ramond (KR) field and perfect fluid dark matter (PFDM). Using M87$^\ast$ shadow data from the Event Horizon Telescope (EHT), we constrain the LSB factor $τ$ and PFDM parameter $ζ$ at 1$σ$ confidence. By combining the sixth-order WKB approximation method with timedomain numerical integration, we systematically compute the complex frequency spectrum of QNMs for black holes in this spacetime background. The numerical results reveal an intriguing conclusion: as the LSB factor $τ$ or the PFDM parameter $ζ$ increases, both the real part and the absolute value of the imaginary part of the QNMs frequencies exhibit a monotonic increase, demonstrating a unique "stiffening" effect. This characteristic stands in stark contrast to the decreasing trend of QNMs frequencies observed in models that consider only traditional dark matter, revealing the critical influence of the coupling between the KR field and PFDM on the dynamic evolution of black holes. This study not only enriches and deepens the understanding of black hole perturbation theory within the framework of modified gravity but also, by identifying the distinctive spectral features of QNMs, offers the potential to distinguish whether the KR field and dark matter are coupled in future observations. Thus, it provides a theoretical foundation for testing mechanisms of spacetime symmetry breaking beyond the standard model and for exploring the nature of dark matter.

gr-qc↗

arXiv2026

Dynamics of thin accretion disks and accretion around a charged-PFDM black hole

This paper investigates the dynamical behavior of steady spherical accretion onto a static, magnetically charged black hole embedded in a perfect fluid dark matter (PFDM) background. Using the shadow observations of M87* from the Event Horizon Telescope (EHT), we establish constraints on the parameter space for the magnetic charge and the PFDM parameter. Within this constrained range, we analyze the orbital dynamics of particles in a thin accretion disk surrounding the black hole and find that the black hole parameters significantly influence the effective potential, angular velocity, specific energy, and specific angular momentum of the particles. Subsequently, we calculate the radiative energy flux, temperature profile, and observed spectrum of the disk. Our results show that, while the local radiative flux and temperature at a given radius are lower for the charged-PFDM black hole compared to a Schwarzschild black hole, its overall radiative efficiency and total luminosity are higher. Finally, we explore the spherically symmetric, steady-state accretion process around the black hole, revealing how the parameters govern how the fluid velocity, density profile, and black hole mass accretion rate are influenced.

astro-ph.HE↗

arXiv2025

Novel topological subclass in Hourava-Lifshitz black holes

This work explores the universal classification of thermodynamic topology for charged static black holes within the $z=3$ Hourava-Lifshitz gravity theory, considering both canonical and grand canonical ensembles. We introduce a new topological subclass, denoted as $\ddot{W}^{1-}$. This finding expands the existing topological classification, going beyond the five previously defined classes and their respective subclasses. The $\ddot{W}^{1-}$ subclass presents a distinct and previously unobserved stability profile: In the low-temperature regime, an unstable small black hole appears in the phase space, whereas, while in the high temperature regime, two unstable small black holes exist together with a stable large black hole. Our study underscores the dependence of charged black hole stability on the selection of the ensemble. These results contribute to refining and expanding the topological framework in black hole thermodynamics, providing key perspectives on the underlying nature of black holes and gravity.

gr-qc↗