arXiv subjects

Sen Guo

Publications and source records attributed to Sen Guo.

At least 37 records · Page 2Linked to original sources

arXiv2024

Image of the Kerr-Newman black hole surrounded by a thin accretion disk

The image of a Kerr-Newman (KN) black hole (BH) surrounded by a thin accretion disk is derived. By employing elliptic integrals and ray-tracing methods, we analyze photon trajectories around the KN BH. At low observation inclination angles, the secondary image of particles is embedded within the primary image. However, as the inclination increases, the primary and secondary images separate, forming a hat-like structure. The spin and charge of the BH, along with the observer's inclination angle, affect the image's asymmetry and the distortion of the inner shadow. To investigate the redshift distribution on the accretion disk, we extended the inner boundary of the accretion disk to the event horizon. The results show that the redshift distribution is significantly influenced by the observation inclination angle. Furthermore, we conducted a detailed analysis of the KN BH image using fisheye camera ray-tracing techniques and found that the optical appearance and intensity distribution of the BH vary at different observation frequencies (specifically at 230GHz and 86GHz). We also examined differences in intensity distribution for prograde and retrograde accretion disk scenarios. Comparing observational at the two frequencies, we found that both the total intensity and peak intensity at 86GHz are higher than those at 230GHz.

astro-ph.HE↗

arXiv2024

Optical appearance of numerical black hole solutions in higher derivative gravity

The optical appearance of the numerically black hole solutions within the higher derivative gravity illuminated by an accretion disk context is discussed. We obtain solutions for non-Schwarzschild black holes with r0 = 1, r0 = 2, and r0 = 3. Further analysis of spacetime trajectories reveals properties similar to Schwarzschild black holes, while the r0 = 2 black hole exhibits significant differences. The results reveal the presence of a repulsive potential barrier for the black hole, allowing only particles with energies exceeding a certain threshold to approach it, providing a unique gravitational scenario for non-Schwarzschild black holes. Additionally, the optical images are derived through numerical simulations by discussing the trajectories of photons intheblackholespacetime.The distribution of radiation flux and the effects of gravitational redshift and Doppler shift on the observed radiation flux are considered. Interestingly, previous analyses of the optical appearance of black holes were conducted within the framework of analytic solutions, whereas the analysis of numerical black hole solutions first appears in our analysis.

gr-qc↗

arXiv2024

Rastall gravity: accretion disk image in radiation fields context and visual transformations compared to Reissner-Nordstrom black holes

Our study investigates the astronomical implications of Rastall gravity, particularly its behavior amidst a radiation field compared to Reissner-Nordstrom (RN) black holes. Our research delineates a crucial correlation between the dynamics of the accretion disk and the parameters Q and N_{\rm r}, which aptly reflect the influence of spacetime metrics on the disk's appearance. Elevated electric charge Q prompts contraction in the disk's orbit due to enhanced gravitational effects, while higher N_{\rm r} values lead to outward expansion, influenced by the radiation field's attributes. Interestingly, the charged black holes surrounded by radiation fields display distinct visual disparities from RN black holes. Brightness decreases and expansion occurs within the accretion disk's innermost stable circular orbit with rising N_{\rm r} values. Our study also reveals the process by which the accretion disk transitions from a conventional disk-like structure to a hat-like form at different observation angles, with the redshift effect gradually intensifying. Moreover, the results of the Rastall gravity radiation field we consider are consistent with the constraints of the host galaxy's gravitational lensing on the Rastall gravity parameters, enhancing the consistency between theoretical predictions and actual observations.

gr-qc↗

arXiv2024

Influence of quantum correction on the Schwarzschild black hole polarized image

Using a model of an accretion disk around a Schwarzschild black hole, the analytic estimates for image polarization were derived by Narayan $et~al.$. [Astrophys. J, 102, 912 (2021)]. Recently, the EHT team also obtained polarization images of the Sgr A$^{*}$ and measured both linear and circular polarization [Astrophys. J. Lett, 964, L25 (2024)]. We find that quantum correction effects can also influence polarization information. Considering the quantum corrected Schwarzschild black hole (Kazakov-Solodukhin black hole), we derive the polarization intensity of the target black hole and investigate polarization images under different parameters. It is found that a larger quantum deformation leads to an expansion of the polarization region, while the polarization intensity value decrease. Under different observation angles, magnetic fields, fluid direction angles, and fluid velocity conditions, we also derive polarization images of corrected black holes. These key indicators not only affect the intensity of polarization but also the direction of polarization. We establish the relationship between polarization intensity and quantum correction deformation parameters, revealing a gradual decline in polarization intensity with reduced radius and an anti-polarization behavior induced by the progressive increase in deformation parameters at a constant radius. Our analysis may provide observational evidence for quantum effect of general relativity.

gr-qc↗

arXiv2023

Influence of accretion disk on the optical appearance of the Kazakov-Solodukhin black hole

The optical characteristics of the Kazakov-Solodukhin (KS) black hole (BH) surrounded by a thin disk is investigated. By utilizing the ray-tracing technique, we derive the the direct and secondary images to illustrate the influence of observational inclination angle (θ_{0}) and quantum correction parameter (a) on the observable properties. Our calculation involves determining the effective potential, light deflection, and azimuthal angle of the BH, as well as the radiation flux of the accretion disk. By assuming three function models, we determine that the exponential function is the most suitable for describing the relationship between the observed flux and the quantum deformation parameter. Our research reveals that the observable characteristics of a BH are affected not only by the shape of the accretion disk, but also by its spatiotemporal properties and the observer's inclination angle. We observe that a BH encircled by an optically thick accretion disk yields different results from those of an optically thin disk.

gr-qc↗

arXiv2023

Unveiling the unconventional optical signatures of regular black holes within accretion disk

The optical characteristics of three types of black holes (BHs) surrounded by a thin accretion disk are discussed, namely the Schwarzschild BH, Bardeen BH, and Hayward BH. We calculate the deflection angle of light as it traverses the vicinity of each BH using numerical integration and semi-analytical methods, revealing that both approaches can effectively elucidate the deflection of light around the BH. We investigate the optical appearance of the accretion disk and its corresponding observational images at various viewing angles, discovering that the luminosity in the region near the BH on the inner side of the accretion disk is higher than that on the outer side owing to higher material density in closer proximity to the BH. We observe a significant accumulation of brightness on the left side of the accretion disk, attributed to the motion of matter and geometric effects. Our findings emphasize the significant influence of the observation inclination angle on the observed outcomes. An increase in the observation inclination angle results in the separation of higher-order images. With the improvement in EHT observation accuracy, we believe that the feature of a minimal distance between the innermost region of the direct image of the Hayward BH and the outermost region of the secondary image can be used as an indicator for identifying Hayward BHs.

gr-qc↗

arXiv2023

Optical appearance of a thin-shell wormhole with a Hayward profile

The optical properties of a thin-shell wormhole (TSW) with a Hayward profile is investigated. Adopting the ray-tracing method, we demonstrate that the TSW's contralateral spacetime is capable of reflecting a significant portion of light back to the observer spacetime. We analyze the effective potential, light deflection, and azimuthal angle of the TSW and find that these quantities are affected by the mass ratio of the black holes (BHs). Specifically, if the mass of the contralateral spacetime BH is greater than that of the original spacetime BH, and the impact parameter satisfies the condition $Hb_{\rm c2}<b_{1}<b_{\rm c1}$, the trajectory of the photon exhibits round-trip characteristics. Assuming the presence of a thin accretion disk surrounding the observing spacetime BH, our results indicate that the image formed by the TSW exhibits additional photon rings and a lensing band compared to an image produced by a BH alone.

gr-qc↗

arXiv2023

Optical appearance of the Schwarzschild black hole in the string cloud context

The image of a black hole (BH) consists of direct and secondary images that depend on the observer position. We investigate the optical appearance of a Schwarzschild BH in the context of a string cloud to reveal how the BH's observable characteristics are influenced by the inclination angle, string cloud parameter, and impact parameter. Following Luminet's work [Astron. Astrophys. 75, 228 (1979)], we adopt a semi-analytic method to calculate the total bending angle of the light ray and derive the direct and secondary images of the Schwarzschild string cloud BH. Our results show that an increase in the inclination angle leads to a more pronounced separation of the images. We consider the gravitational redshift and present the redshift distribution of the direct image while illustrating the flux distribution. We observe that the direct image exhibits blueshift and redshift simultaneously, and the asymmetry of the flux distribution increases with the inclination angle. Finally, we obtain the Schwarzschild string cloud BH image via a numerical simulation, which provides an approximate illustration of the EHT resolution.

gr-qc↗

arXiv2023

Phase transition grade and microstructure of AdS black holes in massive gravity

Considering that under the framework of the massive gravity theory, the interaction between the mass gravitons and Schwarzschild black hole (BH) could make it carry a scalar charge, the phase transition process caused by this scalar charge is investigated in this analysis. The phase transition grade and microstructure of those BHs are investigated from both macroscopic and microscopic points of view. From the macroscopic point of view, it is found that Ehrenfest equations are satisfied at the phase transition critical point, which implies that the phase transition grade of those BHs is second-order. Based on the BH molecules model and Landau continuous phase transition theory, the phase transition of those BHs from the microcosmic point of view is analyzed. The critical exponents obtained from the two perspectives are consistent. By investigating the Ruppeiner geometry, the microstructure feature of those BHs is revealed. These results suggest that the phase transition of BH in massive gravity is a standard second-order phase transition at the critical point, and the microscopic details of those BHs are different from the RN-AdS BH in standard Einstein gravity.

gr-qc↗

arXiv2022

QED and accretion flow models effect on optical appearance of Euler-Heisenberg black holes

Taking the quantum electrodynamics (QED) effect into account, we investigate the geometrical-optics appearance of the Euler-Heisenberg (EH) black hole (BH) under the different accretion flows context, which depends on the BH space-time structure and different sources of light. The more significant magnetic charge leads to the smaller shadow radius for the EH BH, while the different values of the EH parameter do not ruin it. Different features of the corresponding two-dimensional shadow images are derived for the three optically thin accretion flow models. It is shown that the total observed intensity in the static spherical accretion flow scenario leads than that of the infalling spherical accretion flow under same parameters, but the size and position of the EH BH shadows do not change in both of these accretions flows, implying that the BH shadow size depends on the geometric space-time and the shadows luminosities rely on the accretion flow morphology. Of particular interest is that a thin disk accretion model illuminated the BH, we found that the contribution of the lensing ring to the total observed flux is less than 5\%, and the photon ring is less than 2\%, indicating that the direct emission dominates the optical appearance of the EH BH. It is also believed that the optical appearance of the BH image depends on the accretion disk radiation position in this scenario, which can serve as a probe for the disk structure around the active galactic nucleus (AGN) of M87^{*} like.

gr-qc↗

arXiv2022

High-order QED correction impacts on phase transition of the Euler-Heisenberg AdS black hole

Two-phase transition branches of the Euler-Heisenberg (EH) anti-de Sitter (AdS) black hole (BH) were derived from its phase transition critical behavior by Magos et al. [Phys. Rev. D. 102, 084011 (2020)]. We found that the phase transition is unstable. Considering the high-order quantum electrodynamics (QED) correction, we re-derive the EHAdS BH solution and investigate its critical thermodynamic quantities. It is found that the corrected EHAdS BH has only one stable phase transition branch, and its critical exponents are equivalent to that of the vdW system. From the microscopic point of view, we also derive its normalized scalar curvature based on the Ruppeiner geometry. Different from two concave surfaces of the scalar curvature without considering the high-order QED correction, we show that the corrected Ruppeiner geometry has only one concave surface. Our results indicate that the phase transition instability derived by Magos $et~al.$ is due to without considering the high-order QED correction.

hep-th↗

arXiv2022

Comparison of thermodynamic behaviors of two regular-AdS black holes

Considering the negative cosmological constant of an anti-de Sitter (AdS) background as a positive thermodynamic pressure in the extended phase space, we study the thermodynamic behaviors of the regular Hayward-AdS (HAdS) black hole (BH) by investigating $P-\upsilon$ critical and cooling-heating phase transition. We compare the difference of two thermodynamic processes between the HAdS BH and the Bardeen-AdS (BAdS) BH. It is found that the phase transition of the BAdS BH tends to be more the van der Waals (vdW) phase transition. For the cooling-heating phase transition, we find the inversion curves of the HAdS BH are always higher than the BAdS BH under the same pressure and magnetic charge. We also compare the smallest existence mass, the zero-temperature remnant, and the critical magnetic charge. The results suggest that the inner horizon and the outer horizon of the Hayward BH are easier to merge, and the singularity is easier to expose.

hep-th↗

arXiv2022

Ehrenfest's scheme and microstructure for regular-AdS black hole in the extended phase space

The regular (Bardeen)-AdS (BAdS) black hole (BH) in the extended phase space is taken as an example for investigating the BH phase transition grade from both macroscopic and microscopic points of view. The equation of state and thermodynamic quantities of this BH are obtained. It is found that the BAdS BH phase space in the extended phase space should be a second-order phase transition near the critical point by verifying the Ehrenfest's equation, and the possibility of its first-order phase transition can be ruled out by the entropy continuity and the heat capacity mutation. The critical exponents from the microscopic structure are analytically and numerically presented with the Landau continuous phase transition theory by introducing a microscopic order-parameter.

gr-qc↗

arXiv2022

The shadow and photon sphere of the charged black hole in Rastall gravity

Considering a charged black hole (BH) surrounded by a perfect fluid radiation field (PFRF) in Rastall gravity, we investigate this BH shadow and photon sphere on different spherical accretions backgrounds. The effect of the PFRF parameter/BH charge on the critical impact parameter is studied by investigating the light deflection near this BH. The luminosity of these BH shadows in different spherical accretions is obtained, respectively. It is found that the shadow of this BH with infalling spherical accretion is darker than static spherical accretion, and the photon sphere with infalling spherical accretion is brighter than a static one. We creatively investigate the effects of the BH charge/PFRF parameter on the luminosity of BH shadow and photon sphere. The results implying that the BH shadow is a signature of space-time geometry, and the photon sphere luminosity is affected by accretion materials and BH itself.

gr-qc↗

arXiv2022

Observable characteristics of the charged black hole surrounded by thin disk accretion in Rastall gravity

The observable characteristics of the charged black hole (BH) surrounded by a thin disk accretion are investigated in the Rastall gravity. We found that the radii of the direct emission, lensing ring, and photon ring dramatically increased as the radiation field parameter increases, but they only weakly depend on the BH charge. Three positions of the radiation accretion disk relative to the BH are considered, i.e., the innermost accretion disk is closed to the radii of the innermost stable circular orbit, the photon ring of the BH, and the event horizon of the BH. The observed images in three cases respectively are obtained. It is found that the total observed flux is dominated by the direct emission, the lensing ring provides a small contribution, and the photon ring is negligible. The lensing and photon rings could not be observed in the blurred image with the EHT resolution. Our results suggest that the observable characteristics of the charged BH surrounded by the thin disk accretion in the Rastall gravity depend on both the BH space-time structure and the position of the radiating accretion disk with respect to the BH. The research of these BH images may serve as a probe for the BH-disk structure in M87$^{*}$ like nearby active galactic nuclei.

astro-ph.HE↗

arXiv2022

Influence of Accretion Flow and Magnetic Charge on the Observed Shadows and Rings of the Hayward Black Hole

The feature of the observed shadows and rings of an astrophysical black hole (BH) may depend on its accretion flows and magnetic charge. We find that the shadow radii and critical impact parameters of the Hayward BH are decreased with the increase of the magnetic charge. Comparing the Schwarzschild BH with the Hayward BH using the ray-tracing method, we show that the density and deflection of lights increase with the magnetic charge, and the BH singularity does not affect the generation of the shadow. Based on three optically thin accretion flow models, the two-dimensional shadows in celestial coordinates are derived. It is found that the shadow and photon ring luminosities of a Hayward BH surrounded by infalling spherical accretion flow are dimmer than that of a static spherical accretion flow. Taking three kinds of inner radii at which the accretion flow stops radiating, we find that the observed luminosity of a Hayward BH surrounded by a thin disk accretion flow is dominated by the direct emission, and the photon ring emission has a weak influence on it. These results suggest that the size of the observed shadow is related to the space-time geometry, and the luminosities of both the shadows and rings are affected by the accretion flow property and the BH magnetic charge.

astro-ph.HE↗

arXiv2022

Shadow thermodynamics of AdS black hole in regular spacetime

The dependence of the black hole (BH) shadow and thermodynamics may be structured in the regular spacetime. Taking the regular Bardeen-AdS BH as an example, the relationship between the shadow radius and the event horizon radius is derived. It is found that these two radii display a positive correlation, implying that the BH temperature can be rewritten as a function of shadow radius in the regular spacetime. By analyzing the phase transition curves under the shadow context, we found that the shadow radius can replace the event horizon radius to present the BH phase transition process, and the phase transition grade can also be revealed by the shadow radius, indicating that the shadow radius may serve as a probe for the phase structure in the regular spacetime. Utilizing the temperature-shadow radius function, the thermal profile of the Bardeen-AdS BH is established. We obtained that the temperature shows an N-type change trend in P<Pc situation. These results suggest that the phase transition process of the regular AdS BH can be completely presented in the thermal profile, and the relationship between the BH shadow and thermodynamics can also be established in the regular spacetime.

gr-qc↗

arXiv2022

The feature of shadow images and observed luminosity of the Bardeen black hole surrounded by different accretions

In this paper, by exploring the photon motion in the region near the Bardeen black hole, the shadow and observation properties of the black hole surrounded by various accretion models are studied. We analyzed the changes in shadow imaging and observation luminosity when the relevant physical parameters are changed. For the different spherical accretions background, one can find that the radius of shadow and the position of photon sphere do not change, but the observation intensity of shadow in the infalling accretion model is significantly lower than that of the static case. When the black hole is surrounded by an optically and thin disk accretion, the contribution of the photon rings, lensing rings and direct emission to the total observed flux has also been studied. Under the different forms of the emission modes, the result shows that the observed brightness is mainly determined by direct emission, while the lensing rings will provide a small part of the observation flux and the photon ring can provide a negligible observation flux. By comparing our results with the Schwarzschild spacetime, it is found that the existence or change of relevant status parameters will greatly affect the shape and observation intensity of black hole shadow. These results support that the change of state parameter will affect the spacetime structure, thus affecting the observation feature of black hole shadows.

hep-th↗