arXiv subjects

Xiao-Xiong Zeng

Publications and source records attributed to Xiao-Xiong Zeng.

At least 55 records · Page 3Linked to original sources

arXiv2025

Optical Characteristics of the Kerr-Bertotti-Robinson Black Hole

The Kerr-Bertotti-Robinson (Kerr-BR) black hole, a theoretical model of a rotating black hole immersed in a uniform magnetic field, has been proposed recently by Podolsky and Ovcharenko. This study investigates the optical characteristics of the Kerr-BR black hole based on the exact solution. We analyze the optical image under two illumination models: a celestial light source and a geometrically thin accretion disk. We reveal distinct roles for the fundamental parameters in the model. Specifically, it is found that under both illumination models, the effect of the rotation parameter on the optical image of the Kerr-BR black hole is significantly different from that of the magnetic field. As the magnetic field increases, the radii of both the shadow and the Einstein ring enlarge. We also attempt to use the data from M87* and Sgr A* to constrain the magnetic field. These results enhance our understanding of the optical characteristics of the Kerr-BR black hole and establish a theoretical foundation for interpreting future observations on the optical image of the black hole immersed in a uniform magnetic field. Finally, we point out that with advances in the resolution of black hole images, it is possible to detect potential BR-like magnetic fields around black holes.

gr-qc↗

arXiv2025

Energy Extraction via Magnetic Reconnection in Kerr-Sen-AdS$_{4}$ Black Hole: Circular Plasma and Plunging Plasma

In this paper, we investigate the power and efficiency of energy extraction through magnetic reconnection in the Kerr-Sen-AdS$_{4}$ black hole, with a primary focus on both the circular orbit and plunging region. We plot the allowed regions for energy extraction and present corresponding power and efficiency values, comparing them with those of the Blandford-Znajek (BZ) mechanism. Our analysis reveals that energy extraction remains feasible even at a spin parameter as low as 0.5, significantly below previously reported thresholds, and the extracted power can exceed that of the BZ process under certain conditions. Furthermore, the dilatonic scalar charge $b$ and the AdS radius $l$ collectively contribute to lowering the spin threshold for energy extraction. The energy extraction process in the plunging region was further examined by analyzing the permissible energy extraction region, as well as the corresponding power output and efficiency. One can find that the energy extraction is possible even at a spin as low as 0.25. Crucially, parameter $b$ actively lowers the energy extraction spin threshold, while parameter $l$ exerts a counteracting effect, impeding such reduction. This trend shows a marked contrast with circular orbit behavior. Additionally, both power and efficiency in the plunging region consistently surpass those in the circular orbit region, indicating superior energy extraction capability in plunging region.

gr-qc↗

arXiv2025

Kerr-like Black Hole Surrounded by Cold Dark Matter Halo: The Shadow Images and EHT Constraints

Here we provide shadow images of a Kerr-like black hole (BH) in cold dark matter (CDM) halo illuminated with a celestial light source and a thin accretion disk. The impact of spin parameter, critical density and the scale radius on the observed images of BHs is carefully addressed. The results indicate that as spin parameter increases, the circular orbits are shifted rightwards, while the larger values of critical density and the scale radius are the cause to enhance the radius of circular orbits of the BH shadow. In the case of the celestial light source, the impact of critical density on shadow distortion is negligible, but this influence is relatively smaller and becomes appreciable when the scale radius has larger values. Next, we discuss the intensity and the size of the inner shadow, which are gradually increasing with the increase of both parameters. On the other hand, in the case of retrograde flow, the intensity of the shadow images significantly decreases, and a crescent moon emerges on the upper right side of the screen. Subsequently, the distinctive features of red-shift factors for direct and lensed images with prograde and retrograde flows are discussed. The outcomes indicate that the distribution of red-shift factors and the optical appearance are closely related to the behavior of accreting flow as well as to relevant parameters.

gr-qc↗

arXiv2025

A Novel Jet Model for the Novikov-Thorne Disk and its Observable Impact

Recent high-resolution observations have established a strong link between black hole jets and accretion disk structures, particularly in the 3.5 mm wavelength band [Nature. 616, 686 (2023)]. In this work, we propose a ``jet-modified Novikov-Thorne disk model'' that explicitly incorporates jet luminosity into the accretion disk radiation framework. By integrating synchrotron radiation from relativistic electrons in the jet, we derive a modified luminosity function that accounts for both the accretion disk and jet contributions. Our analysis demonstrates that the inclusion of jet luminosity enhances the total accretion disk luminosity by approximately 33.5\%, as derived from the integration of radiative flux. Furthermore, we compare our modified model with the standard Novikov-Thorne model and find that the jet contribution remains significant across different observational inclinations. These results highlight the necessity of incorporating jet effects when estimating the observable flux of black hole accretion systems, which has direct implications for future astronomical observations.

astro-ph.HE↗

arXiv2025

Holographic image features of an AdS black hole in Einstein-power-Yang-Mills gravity

By utilizing the AdS/CFT correspondence, we investigate the holographic image of an AdS black hole in Einstein-power-Yang-Mills gravity. The AdS boundary hosts a Gaussian oscillation source, which induces a lensed response on the opposite side of the boundary during propagation through bulk spacetime. The optical system assists observers at the north pole to continuously capture holographic images that show an axisymmetric bright ring known as the Einstein ring. As the observation position shifted, the bright ring gradually transformed into a luminous arc and eventually transitioned into a light point. Simultaneously, we examine the impact of variations in relevant physical quantity on the ring, and present the corresponding brightness curve. The results indicate that as the temperature $T$ and nonlinear Yang Mills charge parameter $q$ increase, the ring radius also increases, while an increase in the chemical potential $u$ leads to a decrease. However, the peak brightness curve of the ring invariably decreases as the values of $T$, $u$, and $q$ increase, albeit to varying degrees. Upon comparing the outcomes of geometric optics, it can be observed that the position of the ring in holography images is consistent with that of the photon ring.

hep-th↗

arXiv2025

The shadow and accretion disk images of the rotation loop quantum black bounce

In this paper, we study the shadow and observational image of the Kerr-like Loop Quantum Gravity (LQG) inspired black bounce with the help of the celestial light source and the thin disk source by employing the backward ray-tracing method. The results indicate that both the LQG parameter alpha and the rotation parameter a contribute to a reduction in the shadow size; however, the influence of a is predominant, while the effect of alpha circular orbit. One can find that the correlation parameter (a, alpha), along with the observer's inclination angle, affect the image's asymmetry and the distortion of the inner shadow. As the inclination increases, the direct and lensed images diverge, creating a structure resembling a hat. Meanwhile, we also investigate the redshift distribution of the direct lensed images of the accretion disk under different parameters and observation angle. The results show that the distribution of redshift and observed intensity is obviously related to the behavior of accretion flow. These results may provide a potential approach to limit black hole parameters, detect quantum gravity effects, and distinguish the LQG black hole from other black hole models.

gr-qc↗

arXiv2025

Holographic Einstein Ring of Quantum Corrected AdS-Reissner-Nordstrom Black Holes in Kiselev Spacetime

This study, grounded in AdS/CFT correspondence, utilizes wave optics theory to explore the Einstein ring of a quantum-corrected AdS-Reissner-Nordström black hole (BH) in Kiselev spacetime. By fixing the wave source on the AdS boundary, the corresponding response function generated on the antipodal side of the boundary is successfully obtained. Using a virtual optical system with a convex lens, the holographic image of the Einstein ring of the BH is captured on a screen. The study also investigates the impact of various physical parameters and the observer's position on the characteristics of the Einstein ring. The results indicate that changes in the observer's position cause the image to transition from an axisymmetric ring to an arc, ultimately converging to a single luminous point. Additionally, the Einstein ring radius decreases with increasing values of the quantum correction parameter $a$, the equation of state parameter $Ω$, temperature $T$, and chemical potential $μ$ , respectively. In contrast, the ring radius increases as the cosmological fluid parameter $c$ increases. Furthermore, the ring radius becomes more distinct as the wave source frequency $ω$ increases. From the perspective of geometric optics, the photon ring of the quantum-corrected AdS-Reissner-Nordström BH in Kiselev spacetime is further studied. Numerical results suggest that the incident angle of the photon ring aligns with that of the Einstein ring.

gr-qc↗

arXiv2025

Revisiting the shadow of Johannsen-Psaltis black holes

The Johannsen-Psaltis (JP) metric provides a robust framework for testing the no-hair theorem of astrophysical black holes due to the regular spacetime configuration around JP black holes. Verification of this theorem through electromagnetic spectra often involves analyzing the photon sphere near black holes, which is intrinsically linked to black hole shadows. Investigating the shadow of JP black holes offers an effective approach for assessing the validity of theorem. Since the Hamilton-Jacobi equation in the JP metric does not permit exact variable separation, an approximate analytical approach is employed to calculate the shadow, while the backward ray-tracing numerical method serves as a rigorous alternative. For JP black holes with closed event horizons, the approximate analytical approach reliably reproduces results obtained through the numerical computation. However, significant discrepancies emerge for black holes with non-closed event horizons. As the deviation parameter $ε_3$ increases, certain regions of the critical curve transition into non-smooth configurations. Analysis of photon trajectories in these regions reveals chaotic dynamics, which accounts for the failure of the approximate analytical method to accurately describe the shadows of JP black holes with non-closed event horizons.

gr-qc↗

arXiv2024

Holographic Einstein Ring of Deformed AdS-Schwarzschild Black Holes

In this work, the wave optics is employed to investigate the Einstein ring of a deformed AdS-Schwarzschild black hole (BH). When the source is fixed on the AdS boundary, one can obtain the corresponding response function generated on the antipodal side of the boundary. By utilizing a virtual optical system equipped with a convex lens, we are able to capture an image of the BH's holographic Einstein ring on the screen. The influence of the relevant physical parameters and the observer's position on the characteristics of the Einstein ring is also investigated, revealing that variations in the observer's position result in a transition of the displayed image from an axisymmetric ring to an arc, ultimately converging into a solitary point of luminosity. In addition, variations in the relevant physical parameters naturally exert influences on the Einstein ring. The photon ring of the BH was also investigated from a geometric optics perspective, and the numerical results indicate that the incident angle of the photon ring aligns with that of the Einstein ring. In the context of modified gravity theories, the investigation of Einstein rings formed by deformed AdS-Schwarzschild BH is expected to not only contribute to advancing the development of gravitational theories but also facilitate a more comprehensive understanding of spacetime geometry and the physical properties of BHs, thereby distinguishing them from Schwarzschild BH.

hep-th↗

arXiv2024

Holographic images of a charged black hole in Lorentz symmetry breaking massive gravity

Using the AdS/CFT correspondence, this paper investigates the holographic images of a charged black hole within the context of Lorentz symmetry breaking massive gravity. The photon rings, luminosity-deformed rings, or light points from various observational perspectives are obtained. We also study the influences of both the chemical potential and temperature on the Einstein ring. Unlike the previous work, which primarily examines the effect of chemical potential on ring radius at high temperatures and find no change in the radius with varying chemical potential, we also investigate the effect of chemical potential on the ring radius at low temperature besides at high temperature. Our findings indicate that at low temperatures, the photon ring radius decreases with increasing of chemical potential, while at high temperatures, the results are consistent with previous studies. Additionally, we explore the impact of the model parameter λ on the Einstein ring radius and find the the ring radius increases as the model parameter λ increases. More interestingly, for the large chemical potential, u = 1, the temperature dependence of the photon ring radius is reversed for λ = 2 and λ = 4. Conversely, for a small chemical potential u = 0.1, the temperature dependence of the Einstein ring stays the same as λ = 2 and λ = 4.

gr-qc↗

arXiv2024

Observational features of the rotating Bardeen black hole surrounded by perfect fluid dark matter

By employing ray-tracing techniques, we investigate the shadow images of rotating Bardeen black holes surrounded by perfect fluid dark matter. In this work, two models are considered for the background light source, namely the celestial light source model and the thin accretion disk model. Regarding the celestial light source, the investigation focuses on the impact of variations in relevant parameters and observed inclination on the contour and size of the shadow. For the thin accretion disk model, the optical appearance of a black hole is evidently contingent upon the radiative properties exhibited by the accretion disk, as well as factors such as observed inclination and relevant parameters governing spacetime. With an increasing observation inclination, the observed flux of direct and lensed images of the accretion disk gradually converge towards the lower region of the image, while an increase in the dark matter parameter $a$ significantly expands the region encompassing both direct and lensed images. Furthermore, the predominant effect is redshift at lower observation angles, whereas the blueshift effect only becomes apparent at higher observation angles. Simultaneously, the increase in the observation inclination will amplify the redshift effect, whereas an increase in the magnetic charge $\mathcal{G}$, rotation parameter $a$ and the absolute value of dark matter parameter $α$ will attenuate the redshift effect observed in the image. These observations of a rotating Bardeen black hole surrounded by perfect fluid dark matter could provide a convenient way to distinguish it from other black hole models.

astro-ph.HE↗

arXiv2024

Shadow Images of Ghosh-Kumar Rotating Black Hole Illuminated By Spherical Light Sources and Thin Accretion Disks

This study investigates the astronomical implications of the Ghosh-Kumar rotating Black Hole (BH), particularly its behaviour on shadow images, illuminated by celestial light sources and equatorial thin accretion disks. Our research delineates a crucial correlation between dynamics of the shadow images and the parameters $a$,~ $q$ and the $θ_{obs}$, which aptly reflect the influence of the model parameters on the optical features of shadow images. Initially, elevated behavior of both $a$ and $q$ transforms the geometry of the shadow images from perfect circles to an oval shape and converges them towards the centre of the screen. By imposing the backward ray-tracing method, we demonstrate the optical appearance of shadow images of the considering BH spacetime in the celestial light source. The results demonstrate that the Einstein ring shows a transition from an axisymmetric closed circle to an arc-like shape on the screen as well as producing the deformation on the shadow shape with the modifications of spacetime parameters at the fixed observational position. Next, we observe that the attributes of accretion disks along with the relevant parameters on the shadow images are illuminated by both prograde and retrograde accreting flow. Our study reveals the process by which the accretion disk transitions from a disk-like structure to a hat-like shape with the aid of observational angles. Moreover, with an increase of $q$, the observed flux of both direct and lensed images of the accretion disk gradually moves towards the lower zone of the screen. Furthermore, we present the intensity distribution of the redshift factors on the screen. Our analysis suggests that the observer can see both redshift and blueshift factors on the screen at higher observational angles, while augmenting the values of both $a$ and $q$, enhancing the effect of redshift on the screen.

astro-ph.HE↗

arXiv2024

Holographic Einstein Ring of a Charged Rastall AdS Black Hole with Bulk Electromagnetic Field

We study the Einstein images of a charged Rastall AdS black hole (BH) within the fabric of AdS/CFT correspondence. Considering the holographic setup, we analyze the amplitude of the total response function for various values of model parameters. With an increase in parameter $λ$ and temperature $T$, the amplitude of the response function is decreased, while it is increased with the increase of the electric charge $e$ and chemical potential $μ$. The influence of frequency $ω$ also plays an important role in the bulk field, as it is found that the decreasing $ω$ leads to an increase in the periods of the waves, which means that the amplitude of the response function also depends on the wave source. The relation between $T$ to the inverse of the horizon $r_{h}$ for the parameter $λ$ is interpreted under fixed values of other involved parameters. These, in turn, affect the behavior of the response function and the Einstein ring, which may be used to differentiate the present work from previous studies. Via a special optical system, we construct the holographic images of the BH in bulk. The obtained results show that the Einstein ring always appears with concentric stripes at the position of the north pole, and this ring transforms into the luminosity-deformed ring or bright light spot when the distant observer lies away from the north pole. Moreover, from the brightness profiles, it is observed that as $λ$ grows, the shadow radius is significantly decreased, while the brightness of the ring is negligibly changed. We further investigate the influence of $T$ and $μ$ on the ring radius. These results reveal that the increasing values of $T$ lead to an increase in the shadow radius and decrease as the values of $μ$ grow. Finally, we finish this work with a discussion of the Einstein ring radius obtained by geometric optics, which is consistent with wave optics.

gr-qc↗

arXiv2023

Holographic Einstein rings of Non-commutative black holes

With the help of the AdS/CFT correspondence, we easily derive the desired response function of QFT on the boundary. Using the virtual optical system with a convex lens, we are able to obtain the image of the black hole from the response function and further study the Einstein ring of the non-commutative black holes. All the results show that there are some common features and different features compared to the previous study of other background black holes. And with the change of the observation position, this ring will change into a luminosity-deformed ring, or light points. In addition to these similarities, there are some different features which are due to the singularity of the event horizon temperature. Explicitly, the relation between temperature and the event horizon $T-z_h$ has two branches when the non-commutative parameter $n$ is fixed. These in turn have an effect on the behavior of the response function and the Einstein ring. However, the amplitude of $|\langle O\rangle|$ increases with the decrease of the temperature $T$ for the left branch of $T-z_h$ relation, while the amplitude of $|\langle O\rangle|$ decreases with the decrease of the temperature $T$ for the right branch. These differences are also reflected in the Einstein ring. Therefore, these differences can be used to distinguish different black hole backgrounds. Furthermore, we show that the non-commutative parameter has an effect on the brightness and the position of Einstein ring.

gr-qc↗

arXiv2023

Holographic study on Einstein ring for a charged black hole in conformal gravity

With the help of AdS/CFT correspondence, the Einstein ring of a charged black hole in conformal gravity has been studied. Imposing an oscillating Gauss source on one side of the AdS boundary which propagates in the bulk, we derive the response function on the other side of the boundary. With the proposed wave optics system, we observe the Einstein ring as expect. The results reveal that when the observer locates at the north pole, the Einstein ring and surrounding concentric stripes always exist. While the observer departs away from the north pole, the ring becomes into a luminosity-deformed ring or light spot. We also investigate the effect of temperature $T$, chemical potential $u$ and gravity-related parameters $c_0$ on the ring radius. We find the ring radius increases with the decrease of the temperature, increase of the chemical potential, and increase of the gravity-related parameters respectively. To check the results in the framework of holography, we investigate the ingong angle of photon at the photon ring via geometric optics and find it is consistent with the angle of Einstein ring obtained via holography.

gr-qc↗

arXiv2023

Investigating shadow images and rings of the charged Horndeski black hole illuminated by various thin accretions

In this paper, we investigate the shadows and rings of the charged Horndeski black hole illuminated by accretion flow that is both geometrically and optically thin. We consider two types of accretion models: spherical and thin-disk accretion flow. We find that in both types of models, the size of the charged Horndeski black hole shadow decreases with the increase of the charge, and it decreases more slowly for the Reissner-Nordström (RN) black hole. In the spherical accretion flow model, we find that the increase of the charge of Horndeski black hole brightens the light ring around it, and it brightens more significantly in comparison with RN black hole. Due to the Doppler effect, the charged Horndeski black holes with accretion flow of radial motion have darker shadows than those with the static accretion flow, but the size of the shadow is not affected by accretion flow motion. In the thin disk-shaped accretion flow model, we find that the brightness of the light ring around the charged Horndeski black hole is dominated by the direct emission from the accretion flow, and the contribution from lensed rings is relatively small, and that from the photon rings is negligible. We also find that the ring brightness decreases as the charge of Horndeski black hole increases, and the decrease is more significant than that in the RN black hole case. Moreover, the radiation position of the accretion flow can affect the shadow size and the ring brightness of the charged Horndeski black hole.

gr-qc↗

arXiv2023

Holographic Einstein Rings of Black Holes in Scalar-Tensor-Vector Gravity

With the help of AdS/CFT correspondence, we analyze the holographic Einstein images via the response function of the complex scalar field as a probe wave on the AdS Schwarzschild scalar-tensor-vector gravity (STVG) black hole (BH). We find that the amplitude of the response function $|\langle O\rangle|$ decreases with the increasing values of the coupling parameter $α$, while it increases with the decreasing values of temperature $T$. The frequency $ω$ of the wave source also plays a significant role in wave periods, as we increase the values of $ω$, we find a decrease in periods of waves, which means that the total response function closely depends on the wave source. Further, we investigate the optical appearance of the holographic images of the BH in bulk. We found that the holographic ring always appears with the concentric stripe surrounded when the observer is located at the north pole, and an extremely bright ring appears when the observer is at the position of the photon sphere of the BH. With the change of the observational angle, this ring will change into a luminosity-deformed ring or a bright light spot. The corresponding brightness profiles show that the luminosity of the ring decreases, and the shadow radius increases with increasing values of $α$. The relation between temperature $T$ and the inverse of the horizon $h_{e}$ is discussed, which shows the smaller values at the beginning of the horizon $h_{e}$, and then increases as the horizon radius increases. This effect can be used to distinguish the STVG BH solution from other BH solutions. Moreover, these significant features are also reflected in the Einstein ring and the corresponding brightness profiles. In addition, we compare the results obtained by wave optics and geometric optics, which are aligned well, implying that the holographic scheme adopted in this paper is valid.

gr-qc↗

arXiv2023

Holographic Einstein Rings of an AdS Black Hole in Massive Gravity

In the context of holography, the Einstein ring of an AdS black hole (BH) in massive gravity (MG) is depicted. An oscillating Gaussian source on one side of the AdS boundary propagates in bulk, and we impose a response function to explain it. Using a wave optics imaging system, we obtain the optical appearance of the Einstein ring. Our research reveals that the ring can change into a luminosity-deformed ring or light spots depending on the variation of parameters and observational positions. When observers are positioned at the north pole, the holographic profiles always appear as a ring with concentric stripe surroundings, and a bright ring appears at the location of the photon sphere of the BH. These findings are consistent with the radius of the photon sphere of the BH, which is calculated in geometrical optics. Our study contributes to a better understanding of the analytical studies of holographic theory, which can be used to evaluate different types of BHs for a fixed wave source and optical system.

gr-qc↗