We investigate quasinormal modes, late-time tails, and grey-body factors for massive scalar perturbations in the background of the Dymnikova regular black hole. By applying both the time-domain integration and the WKB method with Padé improvements, we show that the spectrum of massive fields differs qualitatively from the massless case. The oscillation frequency of the dominant mode grows with the field mass <italic>&#956;</italic>, while the damping rate decreases, suggesting the existence of quasi-resonances at sufficiently large <italic>&#956;</italic>. In the time domain, the late-time signal exhibits oscillatory tails with a power-law envelope, whose decay rate matches analytic expectations. Grey-body factors are also computed, showing strong suppression of radiation when mass is increased. Taken together, these results indicate that massive fields provide distinctive signatures of regular black holes and may serve as probes of near-horizon quantum corrections in the Dymnikova geometry.

Czechia

Bekir Can Lütfüoğlu

Uzbekistan

Javlon Rayimbaev

Bekzod Rahmatov

Fayzullo Shayimov

Ikram Davletov

Telling tails and quasi-resonances in the vicinity of Dymnikova regular black hole

In this paper, we examine the behavior of the charged compact star model PSR J0740+6620. To achieve this, we solve the Einstein field equations within an anisotropic framework. We model the star’s structure using a Gaussian density profile. Our analysis focuses on assessing the stability of the star and verifying whether its physical properties are consistent with the conditions required for equilibrium. In particular, we consider the Reissner-Nordstr <math altimg='si4.svg'><mover accent='true'><mi>o</mi><mo>&#168;</mo></mover></math>m spacetime configuration as an outer line element for equilibrium conditions. The important aspect of the work is to investigate the acceptable or non-acceptable regions for radial and tangential sound speeds using the contour plot. This helps us to choose the domain of free parameters involved in our work for further analysis. Conclusively, charged compact stars with a Gaussian density profile do exist in general relativity with Reissner-Nordstr <math altimg='si4.svg'><mover accent='true'><mi>o</mi><mo>&#168;</mo></mover></math>m exterior geometry.

Pakistan

Zoya Asghar

Azerbaijan

Jordan

M. Farasat Shamir

Saudi Arabia

Fatemah Mofarreh

Otaboyev Sirajiddin

Non-singular anisotropic star with Gaussian density profile

In this work, we construct and analyze charged acoustic thin-shell wormholes by employing the cut-and-paste technique on a charged acoustic black hole background. The spacetime geometry is governed by an acoustic deformation parameter <italic>&#958;</italic>, which encodes the effects of the relativistic fluid, together with the electric charge <italic>Q</italic>. The surface pressure as well as energy density at the throat are obtained using the Darmois-Israel formalism, and the equilibrium configurations are examined under linear radial perturbations that maintain spherical symmetry. The stability of the wormhole throat is discussed through the second derivative of the effective potential by imposing a near-horizon constraint of the form <math altimg='si18.svg'><mrow><msub><mi>S</mi><mn>0</mn></msub><mo linebreak='goodbreak'>=</mo><msub><mi>r</mi><mi>h</mi></msub><mo linebreak='goodbreak'>+</mo><mrow><mo>|</mo><mi>u</mi><mo>|</mo></mrow></mrow></math>, where <italic>r<inf>h</inf></italic> represents the acoustically induced horizon radii. We systematically explore stability near four distinct horizon branches and analyze the influence of barotropic, Chaplygin-type and phantom-type variable equations of state. Our results reveal that the acoustic parameter plays a dominant stabilizing role by enhancing the convexity of the effective potential, while the electric charge modulates the size and location of the stability regions. It is shown that stable thin-shell wormhole configurations can exist arbitrarily close to the acoustic horizons for appropriate choices of the model parameters, despite the unavoidable violation of the standard energy conditions.

China

Jiafeng Guo

A. Eid

Arfa Waseem

Sardor Murodov

N. Mustapha

Aybek Seytov

Stability analysis of charged acoustic thin-shell wormholes

In this study, we explore the thermodynamics, massless-particle motion, photon sphere, shadow, and gravitational weak lensing of Schwarzschild BHs embedded in a Hernquist dark matter halo, surrounded by a quintessential field. The spacetime metric is constructed using a modified lapse function incorporating the Schwarzschild term, the Hernquist density profile parameterized by <italic>&#961;<inf>s</inf></italic> and <italic>r<inf>s</inf></italic>, and the quintessential contribution with equation of state parameter <italic>&#969;<inf>q</inf></italic>. We derive the Hawking temperature and heat capacity as functions of the event horizon, revealing the thermodynamic influence of the dark matter halo and quintessence. For massless particles, the photon sphere radius is computed numerically, and shadow contours are constructed to demonstrate environmental deformations of the black hole. In the weak lensing regime, the optical geometry formalism in the equatorial plane is employed to obtain the Gaussian curvature <math altimg='si3.svg'><mi mathvariant='script'>K</mi></math> of the effective two-dimensional metric. The deflection angle <italic>&#945;</italic> is evaluated via a double integral over null geodesics, showing enhanced lensing due to the extended mass of the Hernquist halo and the repulsive effect of quintessence. Our results underscore the diagnostic power of multi-messenger signatures in probing dark matter and quintessence around supermassive black holes.

Shokhzod Jumaniyozov

Jamshid Khasanov

Thermodynamics, geodesics and gravitational weak lensing of kiselev black holes surrounded by hernquist dark matter halos

We address the equilibrium configurations and stability properties of anisotropic compact stars whose interior is described by a modified Chaplygin gas (MCG) equation of state in the framework of the regularized four-dimensional Einstein–Gauss–Bonnet (4DEGB) theory. Applying a quasi-local prescription for the pressure anisotropy, we derive the modified Tolman–Oppenheimer–Volkoff (TOV) equations and integrate them numerically over a large parameter space in the Gauss–Bonnet coupling $$\alpha $$ and the degree of anisotropy $$\beta $$ . We provide mass–radius sequences, mass-compactness, energy density, and pressure profiles, and perform a full stability analysis based on the turning-point criterion, the radial adiabatic index $$\gamma _r$$ , and the radial and transverse sound speeds $$v_r^2$$ and $$v_t^2$$ . Our results show that positive $$\alpha $$ and positive anisotropy $$(\beta > 0)$$ systematically increase the maximum mass and radius, enabling then configurations that exceed $$2\,M_\odot $$ while still obeying causality and the modified Buchdahl bound in 4DEGB gravity. A comparison with the latest astrophysical constraints (NICER, GW170817, GW190814, and massive-pulsar measurements) identifies regions of the $$(\alpha ,\beta )$$ parameter space that are observationally allowable. In conclusion, anisotropic dark-energy stars in 4DEGB gravity provide viable, observationally testable ultra-compact alternatives to normal neutron stars and black holes, and also potentially open rich avenues for further multi-messenger searches for higher-curvature effects.

India

Anirudh Pradhan

Thailand

Takol Tangphati

South Africa

Ayan Banerjee

Dark-energy anisotropic compact configurations in 4D Einstein–Gauss–Bonnet gravity: from structure to observational viability

Investigating the impact of dark matter on gravity near black holes (BHs) using observational evidence and theoretical analysis is a critical area of relativistic astrophysics. Therefore, in this manuscript, we examine the behavior of test particles in the vicinity of magnetized Schwarzschild BHs within the framework of scalar-vector-tensor gravity (STVG) theory. We assume that the BH is surrounded by a magnetosphere modeled using the parabolic magnetic field solution. We study the circular motions of test particles near BHs and calculate the corresponding effective potential, accounting for the MOG interaction and the magnetic field’s influence on particle geodesics. In addition, we analyze the stability of circular orbits by evaluating the effective potential, angular momentum, and the particle’s energy. We demonstrate how MOG interactions and the magnetic field affect the location of the innermost stable circular orbits (ISCO). Using the Navikov–Thorne thin accretion disk model, we studied how MOG interactions and the magnetic field affect energy efficiency, energy flux, and temperature distribution. Moreover, we investigate the collision of magnetized particles near our spacetime geometry under the influence of MOG and magnetic fields. Finally, we study the trajectories of charged particles under the influence of MOG interactions and a magnetic field and present our conclusions in the final section.

Saeed Khan

Yunus Turaev

Sulton Usanov

Weiwei Wang

Energy efficiency and particle dynamics around magnetized black holes with parabolic configuration in STVG

The term cosmic dark matter is commonly studied in the context of galactic rotation profiles, particularly along the outer galactic halo. However, its influence may differ significantly in dense-matter astrophysical configurations characterized by strong gravitational fields. In this study, we construct stellar structures developed within the framework of a Dehnen–(1,4,0) halo profile using the well-known Kohler–Chao–Tikekar geometry. The proposed model is driven by an anisotropic fluid coupled with a dark matter component. The aim is to develop the dense-matter, anisotropic astrophysical systems through the framework of geometric decoupling using the minimal geometric deformation scheme. In this context, the temporal component of the auxiliary sector is interpreted as the dark matter sector. A thorough graphic evaluation is conducted to confirm the feasibility of the proposed model, supported by observational data from a set of modeled stellar configurations.

S. Khan

Gravitationally decoupled anisotropic compact stars immersed in Dehnen-(1,4,0) density profiles

This paper investigates the contribution of the nonsingular Yukawa-modified potential in four-dimensional Einstein-Gauss-Bonnet (EGB) gravity, focusing on a static, spherically symmetric black hole solution. These Yukawa-type corrections are described by two parameters, <italic>&#946;</italic> and <italic>&#955;</italic>, that affect Newton&#8217;s law of gravity at large distances, and by a deformation parameter, &#8467; <inf>0</inf>, which is essential at short distances. Primarily, the strongest effect is encoded in <italic>&#946;</italic>, which alters the total mass of the black hole with additional mass proportional to <math altimg='si12.svg'><mrow><mi>&#946;</mi><mi mathvariant='script'>M</mi></mrow></math>, imitating the effects of dark matter at large distances from the black hole. In contrast, the impact due to <italic>&#955;</italic> is small for astrophysical values. On the other hand, EGB gravity is ruled by the Gauss-Bonnet (GB) coupling constant <italic>&#945;</italic>, a fundamental parameter of the theory. We pay particular attention to thermodynamic stability, critical orbits, geodesics, and quasinormal modes. The results demonstrate the stability of the black hole solution for a range of values of the GB coupling constant <italic>&#945;</italic>. Furthermore, this study investigates null geodesic motion, namely the shadow behavior, and provides intriguing results on the size of the black hole shadow.

Yassine Sekhmani

Brazil

A.A. Araújo Filho

Poland

Adam Z. Kaczmarek

Dominik Szczȩśniak

Jurabek Sadullayev

Nonsingular Yukawa-modified black holes surrounded by dark matter in 4D-Einstein-Gauss-Bonnet gravity: Shadow and QNM studies

In this study, we investigate the attributes of compact stars within the configuration of <math altimg='si12.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi>&#966;</mi><mo>)</mo></mrow></math> gravity, by incorporating the Gauss-Bonnet term <italic>G</italic> and a scalar field &#966;. By adopting different functional forms of <math altimg='si12.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi>&#966;</mi><mo>)</mo></mrow></math>, we analyze their impact on the equilibrium structure of dense stellar objects. Further, we adopt the Krori-Barua metric potential, defined as <math altimg='si13.svg'><mrow><mi>&#957;</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>B</mi><msup><mi>r</mi><mn>2</mn></msup><mo linebreak='goodbreak'>+</mo><mi>C</mi></mrow></math> and <math altimg='si14.svg'><mrow><mi>&#955;</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>A</mi><msup><mi>r</mi><mn>2</mn></msup><mo>,</mo></mrow></math> here, <italic>A, B</italic> and <italic>C</italic> are constants. To ensure a physically viable compact configuration, we impose matching conditions between the interior spherically symmetric space-time and the Schwarzschild geometry. Moreover, we investigate the attributes of the celestial star models by assuming the <math altimg='si12.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi>&#966;</mi><mo>)</mo></mrow></math> gravity model. We attain the modified field equations and examine key physical characteristics, namely energy density and pressure components, stability conditions, equation of state, and energy constraints. These findings provide new insights into the viability of alternative gravity models in explaining extreme astrophysical environments and offer potential observational signatures to constrain <math altimg='si12.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi>&#966;</mi><mo>)</mo></mrow></math> gravity through future gravitational wave and electromagnetic observations.

Exploring compact stars in modified <math altimg='si12.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi>&#966;</mi><mo>)</mo></mrow></math> gravity

We investigate the dynamics of charged spinning test particles in the spacetime of a magnetized Bocharova-Bronnikov-Melnikov-Bekenstein black hole (BH), an extremal solution of the Einstein-Maxwell-conformally coupled scalar field equations. Using the Mathisson-Papapetrou-Dixon equations, we derive the equations of motion that incorporate spin-curvature coupling and electromagnetic interactions due to the particle’s charge and an external magnetic field. The effective potential formalism is employed to analyze stable circular orbits, the innermost stable circular orbit (ISCO), and the superluminal bound, ensuring timelike motion. The influence of the particle’s spin <italic>s</italic>, a magnetic coupling parameter <italic>&#969;<inf>B</inf></italic>, is examined numerically, revealing significant shifts in the ISCO radius, specific angular momentum, and energy due to spin and electromagnetic effects. We further study particle collisions near the event horizon, computing the critical angular momentum and center-of-mass energy, which exhibit enhancements akin to the Ba&#241;ados-Silk-West effect, driven by gravitational, electromagnetic, and spin interactions. Our results highlight the intricate interplay of these effects in the BBMB spacetime, offering insights into high-energy astrophysical processes such as accretion disk dynamics and particle acceleration near magnetized BHs.

Munisbek Akhmedov

Spin effects on motion of charged particles around magnetized black holes in conformally coupled scalar fields