Astrophysical black holes (BH) are not isolated, but embedded in matter supplied by their host galaxies. We study how the shape of a surrounding dark matter (DM) halo modifies the ringdown and tidal response of an asymptotically flat, static, spherically symmetric BH. The halo is modelled as an anisotropic Einstein cluster with vanishing radial pressure and a generalized (α,β,γ) density profile, supplemented by an inner cut-off near the BH and, where required, an outer tidal truncation. We derive the axial gravitational perturbation equation and compute the quasinormal mode (QNM) spectrum using sixth-order Wentzel-Kramers-Brillouin (WKB) methods and time-domain evolutions. The halo redshifts both the oscillation frequency and the damping rate, by an amount set not only by the halo compactness but also by the profile parameters: the inner slope γ dominates for centrally concentrated halos, while α and β give subleading but profile-dependent corrections. In the eikonal limit, the shift is governed by a single redshift integral encoding the halo mass distribution outside the light ring, explaining the close correspondence between the QNM frequencies, the light ring frequency, and the Lyapunov exponent. We also show that different combinations of compactness and profile shape can yield nearly degenerate ringdown spectra. Time-domain evolutions confirm the WKB frequencies and display the expected late-time Price law decay, with an intermediate tail controlled by the outer density falloff for slowly decaying profiles. Finally, we compute the static axial tidal Love number and show that it probes the halo with a radial weighting different from the ringdown sector. The combined ringdown and tidal response therefore provides a possible way to distinguish environmental effects from genuine deviations of the vacuum BH geometry.

We study electromagnetic perturbations and the associated quasinormal modes (QNMs) of parametrized static, spherically symmetric wormhole spacetimes, focusing on Damour-Solodukhin and braneworld geometries as well as their galactic extensions. Using the Bronnikov-Konoplya-Pappas parametrization, we express the metric functions in terms of a compactified radial coordinate and characterize the spacetime through far-field and near-throat parameters. The far-field coefficients govern the asymptotic structure and post-Newtonian behaviour, while the near-throat continued-fraction expansion captures the strong-field geometry near the throat. We first apply the parametrization to isolated wormholes and identify its range of validity, showing that non-polynomial metric functions can limit the convergence of the near-throat expansion and hence the accuracy of a truncated representation. We then extend the framework to a galactic Damour-Solodukhin wormhole embedded in a Hernquist dark matter halo. Imposing observational bounds from the shadow of Sgr A$^*$, we constrain the galactic compactness and deformation parameters and obtain an observationally viable parametrized metric. Within the allowed parameter space, we compute the fundamental QNM frequencies using the transfer matrix method and analyze the corresponding time-domain ringdown signals. We find that the damping rate is more sensitive to galactic compactness, whereas the oscillation frequency remains comparatively stable. Although the spectral shifts are small within the shadow-allowed region, the framework provides a systematic link between geometric parametrization, shadow constraints, and dynamical response. Our results establish an observationally consistent parametrized description of wormhole perturbations for strong-field tests of horizonless compact objects.

We investigate the properties of low angular momentum, inviscid, advective accretion flows in a generic static and spherically symmetric spacetime that incorporates higher-order corrections up to the fourth order in 1/r. Employing this metric, we self-consistently solve the relativistic hydrodynamical equations and obtain the family of global transonic accretion solutions (O, A, W, and I types) by means of the spacetime parameters (S, rl, l3) and the flow parameters (specific energy E and angular momentum A). Our analysis reveals that the accretion flow possesses either single or multiple critical points depending on these input parameters. We delineate the regions of the S - A and A - E parameter spaces that admits solutions with multiple critical points and demonstrate how these regions evolve with increasing spacetime parameter S. Furthermore, while connecting the spacetime geometry with observable signatures, we compute the spectral energy distribution (SED) from thermal bremsstrahlung emission and observe that increasing S enhances the SED relative to the Schwarzschild case. Finally, we find that global transonic solutions harboring inner critical points (I types) yield more luminous power than those with only outer critical points (O and A types).

The interplay between supermassive black holes (SMBHs) and their surrounding environment is fundamental to understanding galactic evolution. This work investigates the influence of a cold dark matter (DM) halo on the dynamics of relativistic, low angular momentum, inviscid, and advective hot accretion flow onto a galactic SMBH. Modeling the spacetime geometry as a black hole embedded within various DM distributions, including those with a central density spike, we demonstrate that the presence of a DM halo, particularly one that is massive and compact, enhances the luminosity of the accretion disk. The dominant contribution to this luminosity originates from the inner regions of the flow, suggesting that luminosity measurements could serve as a valuable observational probe for the dense DM environments expected near galactic centers.

We investigate the shadow properties of a wide class of spacetimes arising from different parameter regimes of the generalized Hayward metric, characterized by two independent parameters ( σ , κ ) (Phys. Rev. D 106, 044028). This metric extends the original Hayward regular black hole solution by introducing distinct mass functions in the g tt and g rr components, giving rise to four types of wormholes (which include multi-peak effective potentials), a regular black hole, and a singular black hole solutions allowing for a unified treatment of black hole mimickers. We compute the shadow radii for all spacetimes in vacuum and in the presence of plasma, using both homogeneous and non-homogeneous plasma profiles. Our results show that certain wormhole solutions particularly the Hayward-Damour-Solodukhin class — can exhibit multiple photon spheres, leading to shadow features that differ significantly from the Schwarzschild black hole. When these results are compared with Event Horizon Telescope observations of Sgr A ★ , we find that regular black holes remain observationally viable but only within a narrow parameter space. In contrast, wormhole solutions with multi-peak effective potentials are more consistent with shadow constraints than those with single peaks. This contrasts with quasinormal mode studies, which favored single-barrier potentials, and may imply detectable late-time echoes in gravitational wave signals.

We investigate the physical properties of the central engine powering gamma-ray bursts (GRBs), modeled as a stellar-mass black hole accreting via a neutrino-dominated accretion flow (NDAF). By solving the governing hydrodynamic equations, we obtain global transonic NDAF solutions featuring shock transitions and examine their role in powering GRB energetics. The NDAF solutions are explored over a broad range of black hole parameters, including its mass (MBH) and spin (ak), and accretion rate (M-center dot). We find that shocked NDAFs can naturally account for the observed diversity in GRB energy output. Incorporating results from numerical simulations of binary neutron star and black hole-neutron star mergers, we estimate the remnant black hole mass and spin parameters for the predicted range of postmerger disk mass (Mdisk). Our analysis reveals that small-mass black holes with relatively low spin values can adequately reproduce the luminosities of short GRBs (SGRBs), whereas identical GRB luminosities can also be achieved for more massive black holes possessing higher spin values. Finally, we uncover a robust correlation between the black hole spin and disk mass such that Mdisk decreases with increasing ak, remaining largely independent of the black hole mass (MBH) powering GRBs.

We investigate the relativistic, viscous, advective neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes, incorporating neutrino cooling. By adopting an effective potential to describe the spacetime geometry around the rotating black holes, we self-consistently solve the governing NDAF equations to obtain global transonic accretion solutions. Our findings indicate that, depending on the model parameters, namely, energy (epsilon), angular momentum (lambda), accretion rate ( m ), viscosity (alpha), and black hole spin (ak), NDAFs may harbor standing shocks where the Rankine-Hugoniot shock conditions are satisfied. Utilizing these shock-induced NDAF solutions, we compute the neutrino luminosity (L nu) and neutrino annihilation luminosity ( L nu nu ) across a wide range of model parameters. We further calculate maximum neutrino luminosity ( L nu max ) and neutrino annihilation luminosity ( L nu numax ), resulting in L nu max similar to 1051-53 erg s-1 (1048-51 erg s-1) and L nu numax similar to 1048-52 erg s-1 (1042-49 erg s-1) for ak = 0.99 (0.0). These findings suggest that shocked NDAF solutions are potentially promising to explain the energy output of gamma-ray bursts (GRBs). We employ our NDAF model formalism to elucidate L nu nuobs for five GRBs with known redshifts and estimate their accretion rate ( m ) based on the spin (ak) of the central source of the GRBs studied here.

The environment surrounding a black hole or black hole binaries is generally expected to play an important role in understanding various astrophysical phenomena around them. In this paper, we study relativistic, low angular momentum, inviscid, and advective hot accretion flow onto a galactic supermassive black hole dressed with a cold dark matter halo. Focusing on different relativistic dark matter distributions with an inner density spike, we analyze the effect of the dark matter halo on the topology and properties of the accretion flow. Our results show enhancement of disk luminosity in the presence of dark matter, which depends on the nature and properties (halo mass and compactness) of the dark matter distribution. Under the assumptions of our accretion model, the dominant contribution to the disk luminosity for compact and massive halos arises from the inner regions of the accretion flow. Consequently, our analysis indicates that luminosity measurements can serve as an effective probe of the underlying dark matter density spike.

We explore the potential variation of two fundamental constants, the fine-structure constant and the proton-to-electron mass ratio mu, within the framework of modified gravity theories and finite-temperature effects. Utilizing high-precision white dwarf observations from the Gaia Data Release 3 survey, we construct a robust mass-radius relation using a Bayesian-inspired machine learning framework. This empirical relation is rigorously compared with theoretical predictions derived from scalar-tensor gravity models and temperature-dependent equations of state. Our results demonstrate that both underlying gravitational theory and temperature substantially influence the inferred constraints on alpha and mu. We obtain the strongest constraints as |Delta alpha/alpha| = 2.10(-39.26 )(+32.56)x 10(-7 )and |Delta mu/mu| = 1.61(-34.67 )(+37.16)x 10(-7) and gamma similar or equal to -3.69 x 10(13 )cm(2) for modified gravity parameter , while for the finite temperature case, these are |Delta alpha/alpha| = 1.60(-35.42 )(+37.31)x 10(-7 )and |Delta mu/mu| = 1.23(-35.71 )(+37.02)x 10(-7) for T similar or equal to 1.1 x 10(7 )K. These findings yield tighter constraints than those reported in earlier studies and underscore the critical roles of gravitational and thermal physics in testing the constancy of fundamental parameters.

The kinematics of the ultra-diffuse galaxy (UDG) NGC1052-DF44 is primarily influenced by the presence of dark matter (DM). In this paper, we conduct a contrasting kinematic study of DF44 within the alternative modified gravity framework. In comparison to NFW DM, we test three alternative gravity models viz Milgromian dynamics (MOND), characterized by a known acceleration scale, a generic f(R) model, assuming an expansion of the Ricci scalar, and a quantum gravity-inspired Renormalization Group correction to General Relativity (RGGR), which involves the running of the gravitational coupling parameter G with the Universe's energy scale. For each gravity model, we evaluate the velocity dispersion (VD) of the galaxy beyond the conventional radial isotropic assumption and extend to two anisotropy scenarios, i.e., constant and Osipkov-Merritt. Our results show that all three gravity models can provide consistent fits to the observed VD of DF44; however, only MOND and RGGR remain competitive with NFW DM. Interestingly, the constant anisotropy scenario in all the models is also found to be competitive with the complete isotropic assumption.

We have investigated the characteristics of shadows cast by the Kerr black hole in the presence of plasma and compared them to those of a rotating wormhole in a uniform plasma space-time for an observer at infinity. Interestingly, for the same uniform plasma density, the apparent shadow size of the rotating wormhole is always greater than that of the Kerr black hole. To further distinguish the two compact objects we studied the deflection angle and did a comparative study in the presence of the uniform and non-uniform plasma profiles. The goal of this whole exercise is to deepen our understanding of the observational phenomena of these astrophysical objects. The analysis reveals the importance of specific plasma distribution profiles, the impact of plasma on the shadow diameter, and the behavior of deflection angles in different plasma scenarios. We have calculated constraints on the plasma parameters by considering observational data and employing analytical formulations. Our work therefore provides valuable insights into the behavior of light rays near compact objects in plasma space-time.

The accreting collapsed object GRO J1655-40 could contain the gravitomagnetic monopole (GMM), and it was shown to be better described by the Kerr-Taub-NUT (KTN) spacetime instead of the Kerr spacetime. The warped accretion disk has also been observed for the same collapsed object. Motivated by these, we study a tilted thin inner accretion disk around a KTN black hole. Such a tilting could have a significant effect on the X-ray spectral and timing features via the Lense-Thirring effect. Taking into account the contribution from the inner accretion disk for the KTN black hole, here we calculate the radial profile of a tilt angle. Depending on the numerical values of the viscosity of the accreting material and Kerr parameter, GMM tends the angular momentum of the disk to align along the black hole's spin axis, or to make it more tilted. Our solution for the radial profile of the tilted disk around a KTN black hole could be useful to probe the strong gravity regime, and could also give indirect evidence for the existence of GMM in nature.

Fundamental constants are crucial for comprehending physical mechanisms, but their measurements contain uncertainties due to experimental limitations. We investigate the impact of system temperature on these uncertainties using nearby white dwarfs observed in the Gaia Early Data Release 3 (EDR3) survey. Using the structures of these white dwarfs, we show that the variation in system temperature can affect the accuracy of measurements for fundamental parameters such as the fine-structure constant and the proton-to-electron mass ratio. This exploration emphasizes the importance of considering the energy of a system while putting bounds on the values of fundamental constants.

Renormalization group correction to general relativity (RGGR) proposes a logarithmic running of the gravitational coupling (G), resulting in a modified description of gravity. Analogous to the proposal of dark matter (DM), RGGR has the potential to explain the observed kinematics of the galaxies, including the missing mass problem. We, for the first time, based on the galaxy morphological types, investigate the dynamics of a diverse collection of galaxies present in the Spitzer Photometry for Accurate Rotation Curve (SPARC) catalog. We phenomenologically constrain the RGGR model parameter (nu) along with the mass-tolight ratio for a sample of 93 SPARC galaxies, selected from four different morphological types, viz. early, spiral, late, and starburst. Our statistical analysis finds RGGR to fit the observed galaxy kinematics consistently. Additionally, we observe that for the galaxies where RGGR and Navarro-Frenk-White (NFW) profile fare equally well. RGGR demonstrates a competitive performance compared to the DM model. The constrained RGGR model parameter also supports the claim that it has a near-linear dependence on the galactic baryonic mass. From our morphology study, we find that the parameter nu decreases from the earlytype to the starburst galaxies. Finally, the renormalization group improved gravity is tested against the two established empirical relations for the SPARC catalog, viz., the Radial Acceleration Relation and the Baryonic Tully Fisher relation, and both are found to satisfy consistently. Importantly, these results are found to be nearly independent of the choice of the Bayesian priors on the model parameters.

In this paper, we investigated the holographic fermionic pole-skipping phenomena for a class of interacting theory in a charged AdS black hole background. We have studied two types of fermion-scalar interactions in the bulk: dipole and Yukawa type interaction. Depending upon the interaction we introduced both real and charged scalar fields. We have particularly analyzed the effect of scalar condensation on the fermionic pole-skipping points and discussed their behaviour near critical temperatures.

We present the properties of relativistic, inviscid, low angular momentum, advective accretion flow in a f(R) gravity theory that satisfactorily mimics the asymptotically flat vacuum solutions of the Einstein’s equations. With this, we solve the governing equations describing the accretion flow and obtain the global transonic accretion solutions in terms of flow energy (E), angular momentum (λ) and gravity parameter (A) that determines the effect of f(R) gravity. We observe that depending on the model parameters, flow may contain either single or multiple critical points. We separate the effective domain of the parameter space in λ−E plane that admits accretion solutions possessing multiple critical points and observe that solution of this kind continues to form for wide range of the flow parameters. We examine the modification of the parameter space and reveal that it gradually shrinks with the decrease of A, and ultimately disappears for A=−2.34. Finally, we calculate the disk luminosity (L) considering bremsstrahlung emission process and find that global accretion solutions passing through the inner critical point are more luminous compared to the outer critical point solutions.

Considering ( 1 + 1) -dimensional fluid in presence of gravitational trace anomaly, as an effective description of higher -dimensional fluid, the hydrodynamics is discussed through a first order thermodynamic description. Contrary to the existing approaches which are second order in nature, the fluid velocity is identified through the auxiliary field required to describe the Polyakov action for the effective description of relevant energy -momentum tensor. The thermodynamic and fluid quantities, on a static black hole spacetime, are calculated both near the horizon as well as at the asymptotic infinity. The Unruh vacuum appears to be suitable one for the present analysis, in contrast to Israel -Hartle -Hawking vacuum which is consistent with second order description. As in anomaly cancellation approach to find the Hawking flux the Unruh vacuum is consistent with the required conditions, in reverse way we interpret this fluid description as an alternative approach to find these required conditions to calculate the same in anomaly cancellation approach.

In this paper, we analyze the pole-skipping phenomena of finite temperature Yang-Mills theory with quark flavors, which is dual to D3-D7 brane systems in bulk. We also consider the external electric field in the boundary field theory, which is dual to the world volume electric field on the D7 brane. We will work in the probe limit where the D7 branes do not backreact to the D3 brane background. In this scenario, we decode the characteristic parameters of the chaos, namely, Lyapunov exponent 2L and butterfly velocity vb from the pole-skipping points by performing the near effective horizon analysis of the linearized Einstein equations. Unlike pure Yang-Mills, once charged quarks with a background electric field are added into the system, the characteristic parameters of the chaos show nontrivial dependence on the quark mass and external electric field. We have observed that 2L and vb decreases with increasing electric field. We further perform the pole-skipping analysis for the gauge invariant sound, shear, and tensor modes of the perturbation in the bulk and discuss their physical importance in the holographic context.

In this work, we study the behavior of null geodesics within a rotating Teo wormhole spacetime in nonmagnetized pressureless plasma. The Teo wormholes are an explicit class of rotating wormholes that generalizes the static, spherically symmetric ones, initially considered by Morris and Thorne. By focusing on the dispersion relation of the plasma and disregarding its direct gravitational effects, we examine how light rays traverse in the abovementioned spacetime. A key highlight of the work is the necessity of a specific plasma distribution profile to establish a generalized Carter's constant which represents a conserved quantity for the motion around rotating compact objects, shedding light on the importance of this parameter. Furthermore, we derive analytical formulas to distinguish the shadow boundary across various plasma profiles, uncovering a fascinating trend of diminishing shadow size as plasma density increases. Intriguingly, certain limits of the plasma parameters result in the complete disappearance of the shadow. When calculating the deflection angle by a wormhole in plasma spacetime, we observe a distinct pattern: The angle decreases as the plasma parameter rises in nonhomogeneous plasma spacetime, diverging from the behavior observed in homogeneous plasma spacetime. Also, leveraging observational data from M87*, we establish constraints on the throat radius. Furthermore, minimum shadow size provides valuable constraints for the radial and latitudinal plasma parameters.

This study explores spherically symmetric non-linear electrodynamics black holes and their effects on light propagation. We derive the governing metric, revealing radial coordinate dynamics within the event horizon. We analyze photon trajectories, finding that increasing magnetic charge expands the horizon and emission range. Furthermore, with the help of the Event Horizon Telescope results, we constrain parameters and emission profiles. Direct emission dominates, while lensing rings play a lesser role. Comparing with Schwarzschild black holes, we observe higher intensity but a wider emission region in non-linear electrodynamics black holes. This work enhances our understanding of modified spacetimes and their impact on black hole properties.