arXiv subjects

He-Bin Zheng

Publications and source records attributed to He-Bin Zheng.

4 recordsLinked to original sources

arXiv2025

Shadows and accretion disk images of charged rotating black hole in modified gravity theory

In this paper, we study the shadow and images of the accretion disk of Kerr-Newman (KN) black hole (BH) in modified gravity (MOG) theory by using backward ray-tracing method. And, the influence of spin parameter ($a$), charge ($Q$), and MOG parameter ($α$) on the observed features of BHs are carefully addressed. Interestingly, as $α$ increases, the flat edge of the BH's shadow gradually becomes more rounded, the size of shadow enlarges, and the deviation rate ($δs$) correspondingly decreases. By tracing the photon around BH, we observe that the trajectory of photon exhibits distortion behavior, i.e., the formation of two "tails" near the Einstein ring, which elongate as $a$ increases. For the accretion disk, it shows that the inner shadow expands with $α$, while decreases with $Q$. The increase of $α$ exhibits an increasing effect on redshift. At the same parameter level, $α$ has a more obvious effect on inner shadow and image of BH by comparing with that of $Q$. Our study implies that both $α$ and $Q$ have relatively significant effects on the image of the KN-MOG BH with the thin disk accretion, but the influence of $α$ is much greater. So, this indicates that $α$ plays a dominant role in this spacetime.

gr-qc↗

arXiv2024

Holographic thermodynamics of a charged AdS black holes with global monopole

By regarding the Newton constant $G_{N}$ and cosmological constant $Λ$ as variables, we in this paper study the thermodynamics and phase transition of Reissner-Nordstr$\ddot{o}$m anti-de Sitter (RN-AdS) black hole with global monopole in the framework of AdS/CFT correspondence. It is found that there are interesting critical phenomena and phase behaviors in the (grand) canonical ensembles of fixed ($\tilde Q,{\cal V},C$), ($\tilde Φ,{\cal V},C$) and ($\tilde Q,{\cal V},μ$). When the other parameters are fixed, the free energy decreases with the global monopole increases. In ($\tilde Q,{\cal V},C$) ensemble, the range of unstable region decreases with the increase of global monopole. In ($\tilde Φ,{\cal V},C$) ensemble, when $\tildeΦ < Φ_{c}$, the free energy appears two branches, the upper and lower branches correspond to low entropy and high entropy respectively. When ($\tilde Q,{\cal V},μ$) is fixed, a new zero-order phase transition occurs in the high-entropy phase and the low-entropy phase at certain $μ$-dependent temperatures. When $μ$ increases to a certain value, this zero-order phase transition disappears. This certain value is negatively related to the magnitude of the global monopole. Finally, we find that $p-\cal V$ criticality does not appear with the change of global monopole. Therefore, it is important to note that the CFT states of charged black holes with global monopole do not correspond to Van der Waals fluids. Finally, we find that charged black holes with global monopoles can better reflect thermodynamic phase transitions and critical phenomena under the AdS/CFT correspondence. By adjusting the change of the global monopole, the thermodynamic phase transition will also change.

hep-th↗

arXiv2024

The shadow and observational images of the non-singular rotating black holes in loop quantum gravity

By considering the celestial light source and the thin disk source, we employ the backward ray-tracing method to carefully study the shadow, inner shadow and observational images of the non-singular rotating black holes in loop quantum gravity. The results show that the increase of quantum parameter $λ$ causes the shadow to shrink, while increases the deviation from circularity. And, the shadow's angular diameter of M87* impose stronger constraints on the observed properties of the no-singulgar rotating black holes by comparing with SgrA*. For a celestial light source, the parameter $λ$ indeed influences the distortion of light around black hole shadow, but this effect is relatively small and only becomes noticeable when extremely close to the shadow. When a thin accretion disk around black hole, it turns out that for an observer at any position, the parameter $λ$ has little effect on the shape of the inner shadow. However, it decreases the size of the inner shadow, reduces the observed light intensity, and narrows the redshifted shadow images, regardless of whether the accretion disk is prograde or retrograde. Meanwhile, it is true that the thin disk images of black hole cannot effectively reflect the internal structure of black hole. Finally, we can conclude that a key observational feature of these non-singular rotating black holes is that the larger the black hole's spin parameter, the smaller the upper limit of $λ'$s effect. And, the parameter $λ$ decreases the gravitational field's strength, thereby weakens the observed images. This could provide a possible way to constraining black hole parameters, identifying quantum gravity effects, and distinguishing loop quantum gravity black holes, even if it cannot be used to distinguish the non-singular properties of black hole.

gr-qc↗

arXiv2023

Shadow Thermodynamics of AdS Black Hole with the Nonlinear Electrodynamics Term

In this paper, we have creatively employed the shadow radius to study the thermodynamics of a charged AdS black hole with a nonlinear electrodynamics(NLED) term. First, the connection between the shadow radius and event horizon is constructed with the aid of the geodesic analysis. It turns out that the black hole shadow radius shows a positive correlation as a function of the event horizon radius. Then in the shadow context, we found that the black hole temperature and heat capacity can be presented by the shadow radius. And further analysis shows that the shadow radius can do as well as the event horizon in revealing black hole phase transition process. In this sense, we constructed the thermal profile of the charged AdS black hole with inclusion of the NLED effect. In P < Pc case, it is found that the N-type trend of the temperature given by the shadow radius is always coincide with that obtained by using the event horizon. So, we can concluded for the charged AdS black hole that the phase transition process can be intuitively presented as the thermal profile in the shadow context. Finally, the effects of NLED have been carefully analysed through out the paper.

gr-qc↗