arXiv subjects

Meirong Tang

Publications and source records attributed to Meirong Tang.

33 records · Page 2Linked to original sources

arXiv2024

The Lensing Effect of Quantum-Corrected Black Hole and Parameter Constraints from EHT Observations

The quantum-corrected black hole model demonstrates significant potential in the study of gravitational lensing effects. By incorporating quantum effects, this model addresses the singularity problem in classical black holes. In this paper, we investigate the impact of the quantum correction parameter on the lensing effect based on the quantum corrected black hole model. Using the black holes $M87^*$ and $Sgr A^*$ as our subjects, we explore the influence of the quantum correction parameter on angular position, Einstein ring, and time delay. Additionally, we use data from the Event Horizon Telescope observations of black hole shadows to constrain the quantum correction parameter. Our results indicate that the quantum correction parameter significantly affects the lensing coefficients $\bar{a}$ and $\bar{b}$, as well as the Einstein ring. The position $θ_{\infty}$ and brightness ratio $S$ of the relativistic image exhibit significant changes,with deviations on the order of magnitude of $\sim 1μas$ and $\sim 0.01μas$, respectively. The impact of the quantum correction parameter on the time delay $ΔT_{21}$ is particularly significant in the $M87^*$ black hole, with deviations reaching up to several tens of hours. Using observational data from the Event Horizon Telescope(EHT) of black hole shadows to constrain the quantum correction parameter, the constraint range under the $M87^*$ black hole is $0\le \fracα{M^2}\le 1.4087$ and the constraint range under the $Sgr A^*$ black hole is $0.9713\le \fracα{M^2}\le 1.6715$ . Although the current resolution of the EHT limits the observation of subtle differences, future high-resolution telescopes are expected to further distinguish between the quantum-corrected black hole and the Schwarzschild black hole, providing new avenues for exploring quantum gravitational effects.

gr-qc↗

arXiv2024

Destroying the Event Horizon of Cold Dark Matter-Black Hole System

Since the Weak Cosmic Censorship Conjecture was proposed, research on this conjecture has been ongoing. This paper explores the conjecture in black holes that are closer to those existing in the real universe (i.e., rotating black holes enveloped by dark matter). In this paper, we obtained a first-order corrected analytical solution for the black hole event horizon through an approximate solution. The validity of the first-order corrected analytical solution will be provided in the appendix. We conduct our study by introducing a test particle and a scalar field into the black hole. Our conclusions show that, in extremal case, both a test particle and a scalar field can disrupt the event horizon of the Kerr-like black hole; in near-extremal case, both a test particle and a scalar field can disrupt the event horizon of the Kerr-like black hole. When cold dark matter is not considered, the conclusion is consistent with previous research.

gr-qc↗

arXiv2024

Short-Hair Black Holes and the Strong Cosmic Censorship Conjecture

The singularity problem has always been a focus of physicists' research. In order to solve this problem, Penrose proposed the cosmic censorship conjecture, but verifying this conjecture in different situations still faces many challenges. In the context of short-hair black hole research, this paper explores whether the Strong Cosmic Censorship Conjecture (SCCC) is obeyed by the universe when it is disturbed by a scalar field. In this paper, we explore whether the short-hair black hole satisfies the SCCC under scalar field perturbations. Using the Weak Gravity Conjecture (WGC) and the WKB approximation method within the framework of general relativity, we systematically analyze the behavior of short-hair black holes under different parameter conditions. The focus is on whether violations of the SCCC occur when the black hole approaches extremal conditions. The results show that when the charge Q of the short-hair black hole approaches its extremal value, the SCCC is violated. However, as the order k of the black hole's metric equation and the angular momentum quantum number l increase, the phenomenon of SCCC violation is delayed. These findings indicate that the proximity of the black hole's charge Q to extremality, as well as the values of the angular momentum quantum number l and the order k, play crucial roles in exploring black hole physics and verifying the SCCC. This research not only reveals the behavior of short-hair black holes under extreme conditions but also provides a new perspective for further investigation of the SCCC.

gr-qc↗

arXiv2024

Exploring the Possibility of Testing the No-Hair Theorem with Minkowski-deformed Regular Hairy Black Holes Via Photon Rings

In this paper, we investigate the optical appearance of a regular static spherically symmetric hairy black hole within the context of Minkowski deformation governed by the parameter $α$. This black hole describes a hairy black hole with geometric deformations in the radial and temporal metric components, parameterized by $α$. The optical appearance of the black hole, illuminated by a static thin accretion disk in three toy emission function models, exhibits distinctive shadows and photon rings. Our findings reveal that for static spherically symmetric hairy Minkowski-deformed regular black holes, the event horizon radius $r_h$, photon sphere radius $r_{ph}$, critical impact parameter $b_{ph}$, and innermost stable circular orbit radius $r_{isco}$ all have a positive correlation with $α$. These parameters affect the null geodesic trajectories, shadows, and the optical appearance of the photon rings illuminated by a static thin accretion disk around the black hole. Utilizing this, we obtained the optical appearance of this black hole when observed in the forward direction of the optical and geometric thin accretion disk models. In all three models, the radius of the photon ring images also shows a positive correlation with the parameter $α$. Therefore, under the static spherically symmetric hairy Minkowski-deformed regular black hole, there is no degeneracy of photon rings dependent on the parameter $α$. Theoretically, this allows for the distinction of different spacetime metrics of hairy Minkowski-deformed regular black holes, providing a potential method for testing the no-hair theorem through future observations of black hole photon rings.

gr-qc↗

arXiv2024

The Weak Cosmic Censorship Conjecture in Hairy Kerr Black Holes

The Weak Cosmic Censorship Conjecture, since its proposal, has always been a controversial hypothesis, but its significance in astrophysics is undeniable. For a regular black hole, its center does not contain a singularity, and the destruction of the horizon of such black holes is not protected by the Weak Cosmic Censorship Conjecture. Therefore, we employ Gedanken experiments to study the hairy Kerr black holes, which are promising candidates to serve as "simulators" of astrophysical black holes. By investigating these black holes through testing particles and scalar fields carrying large angular momentum, we explore whether these black holes can achieve overspinning. Our results suggest that the overspinning behavior of these hairy Kerr black holes in extremal or near-extremal conditions strongly depends on the hairy parameters (${α, l_0}$). This not only potentially offers us an opportunity to explore the interior structure of black holes, but may also provide clues for constraining the hairy parameters. This phenomenon might reveal the connection between the no-hair theorem of black holes and the weak cosmic censorship conjecture, bringing new perspectives to our understanding of these theories.

gr-qc↗

arXiv2024

Testing The Weak Cosmic Censorship Conjecture in Short Haired Black Holes

The Weak Cosmic Censorship Conjecture is a hypothesis regarding the properties of event horizons and singularities during the formation of black holes, stating that singularities are always encompassed by the event horizons(TEH) of black holes, thus preventing naked singularities from affecting the causal structure of spacetime. In this paper, we explore the Weak Cosmic Censorship Conjecture in the context of rotating hairy black holes, aiming to understand the impact of hairiness on the conjecture for Kerr black holes. We investigate whether TEH of rotating hairy black holes can be disrupted by incoming test particles and scalar fields. When test particles and scalar fields incident on the rotating hairy black hole are found. In extreme cases, when considering a second order approximation, if the parameter $κ$ (The parameter here is a function related to hair strength $κ(Q_m^{2k})$.)falls within the range of $0<κ<\sqrt{1/3}$, TEH of a hairy black hole can be disrupted. Conversely, in the range of $\sqrt{1/3}<κ<1$, TEH of a hairy black hole cannot be disrupted. When considering the second order approximation in near extreme cases, the parameter $κ$, within the range of $0<κ<1$, can lead to the disruption of TEH in this spacetime. When an incident scalar field is present, in near extreme conditions, TEH of a rotating short hair black hole cannot be disrupted. Therefore, the value of the parameter $κ$ reveals the connection between rotating short hair black holes and the weak cosmic censorship conjecture, indicating that the presence of short hair significantly affects TEH of black holes. This will aid in further understanding the nature of rotating short hair black holes.

gr-qc↗

arXiv2024

Quasinormal modes of dark matter core-black hole spacetime

In the galactic core, when the scale of dark matter is small, the distribution of dark matter is that of a constant density dark matter core.Considering the case of a supermassive black hole coupled to a constant density dark matter core, we study the quasinormal modes of the black hole in the constant density dark matter core black hole system and calculate the quasinormal modes frequency of the black hole using the third order WKB approximation and the prony method.In addition, we study the effect of the constant density dark matter core parameter $r_0$ on the quasinormal modes of black holes in the vicinity of black holes.As the angular quantum number increases, the ringdown process becomes closer and closer to the case of the ringdown process of a schwarzschild black hole.The presence of a constant density dark matter core affects the quasinormal modes of the black hole, with relative deviations on the order of $10^{-15}-10^{-13}$ with respect to the detector.These features suggest that with future improvements in detector accuracy, we can use them for the detection of gravitational waves in the spacetime of constant density dark matter core-black hole systems, which in turn opens up the possibility of understanding the behavior of dark matter in the vicinity of black holes.

gr-qc↗

arXiv2023

Weak cosmic censorship conjecture and black hole shadow for black hole with generalized uncertainty principle

Based on string theory, loop quantum gravity, black hole physics, and other theories of quantum gravity, physicists have proposed generalized uncertainty principle (GUP) modifications. In this work, within the framework of GUP-gravity theory, we have successfully derived an exact solution to Einstein$'$s field equation, discuss the possibility of using EHT to test GUP and how GUP changes the weak cosmic censorship conjecture for black hole. We analyze two different ways of constructing GUP rotating black holes (Model I and Model II). Model I takes into account the modification of mass by GUP, i.e. the change of mass by quantization of space, and the resulting GUP-rotating black hole metric (18) is similar in form to Kerr black hole. Model II takes into account the modification of the rotating black hole when GUP is an external field, where GUP acts like an electric charge, and the resulting GUP-rotating black hole metric (19) is similar in form to Kerr-Newman black hole. By analyzing the shadow shape of the GUP rotating black hole, we have discovered intriguing characteristics regarding the impact of first-order and second-order momentum correction coefficients on the black hole's shadow shape. These findings will be instrumental in future GUP testing using EHT. Additionally, by incident test particle and scalar field with a rotating GUP-black hole, the weak cosmic censorship conjecture is not violated in either extreme black holes or near-extreme black hole.

gr-qc↗

arXiv2023

Test the Weak Cosmic Supervision Conjecture in Dark Matter-Black Hole System

There is a possibility that the event horizon of a Kerr-like black hole with perfect fluid dark matter (DM) can be destroyed, providing a potential opportunity for understanding the weak cosmic censorship conjecture of black holes. In this study, we analyze the influence of the strength parameter of perfect fluid DM on the destruction of the event horizon of a Kerr-like black hole with spinning after injecting a test particle and a scalar field. We find that, when a test particle is incident on the black hole, the event horizon is destroyed by perfect fluid dark matter for extremal black holes. For nearly extremal black holes, when the dark matter parameter satisfies $α\in \left (-r_{h} , 0\right ) \cup \left ( r_{h} ,k_2\right )$ i.e.$(A<0)$, the event horizon of the black hole will not be destroyed; when the dark matter parameter satisfies $α\in\left ( k_1 ,-r_{h} \right ]\cup \left[0,r_{h}\right ]$ i.e.$(A\ge 0)$, the event horizon of the black hole will be destroyed. When a classical scalar field is incident into the black hole in the extremal black hole case, we find that the range of mode patterns of the scalar field that can disrupt the black hole event horizon is different for different values of the perfect fluid dark matter strength parameter. In the nearly extremal black hole case, through our analysis, we have found when $α\neq0 $ and $α\neq\pm\ r_h$ i.e.$A\neq0$, the event horizon of the black hole can be disrupted. Our research results indicate that dark matter might be capable of breaking the black hole horizon, thus potentially violating the weak cosmic censorship conjecture.

gr-qc↗

arXiv2022

The no-hair theorem and black hole shadows

The successful observation of M87 supermassive black hole by the Black Hole Event Horizon Telescope(EHT) provides a very good opportunity to study the theory of gravity. In this work, we obtain the exact solution for the short hair black hole (BH) in the rotation situation, and calculate in detail how hairs affect the BH shadow. For the exact solution part, using the Newman-Janis algorithm, we generalize the spherically symmetric short-hair black hole metric to the rotation case (space-time lie element (2.25)). For the BH shadow part, we study two hairy BH models. In model 1, the properties of scalar hair are determined by the parameters $α_{0}$ and $L$. In model 2, the scalar hair of the BH is short hair. In this model, the shape of the BH shadow is determined by scalar charge $Q_{m}$ and $k$. In general, various BH hairs have different effects on the shadows, such as non-monotonic properties and intersection phenomena mentioned in this work. Using these characteristics, it is possible to test the no-hair theorem in future EHT observations, so as to have a deeper understanding of the quantum effect of BHs. In future work, we will use numerical simulations to study the effects of various hairs on BHs and their observed properties.

gr-qc↗

arXiv2021

Effect of quantum deformed black hole on BH shadow in two-dimensional Dilaton gravity

In recent years, the study of quantum effects near the event horizon of black hole (BH) has attracted extensive attention. It has become one of the important methods to explore BH quantum properties by using the related properties of the quantum deformed black hole. In this work, we study the effect of quantum deformed black hole on BH shadow in two-dimensional Dilaton gravity. In this model, quantum effects are reflected on the quantum correction parameter m. By calculation, we find that: (1) the shape of the shadow boundary of a rotating black hole is determined by the BH spin $a$, the quantum correction parameter $m$ and the BH type parameter $n$; (2) when the spin $a=0$, the shape of the BH shadow is a perfect circle; when $a\neq 0$, the shape is distorted; if the quantum correction parameter $m=0$, their shapes reduce to the cases of Schwarzschild BH and Kerr BH respectively; (3) the degree of distortion of the BH shadow is different for various quantum correction parameters $m$; with the increase of the values of $m$, the shadow will become more and more obvious; (4) the results of different BH type parameter $n$ differ greatly. Since the value of $m$ in actual physics should be very small, the current observations of EHT cannot distinguish quantum effect from BH shadow, and can only constrain the upper limit of $m$. In future BH shadow measurements, it will be possible to distinguish quantum deformed black holes, which will help to better understand the quantum effects of BHs.

hep-th↗

arXiv2021

Rotating spacetime: black-bounces and quantum deformed black hole

Recently, two kinds of deformed schwarzschild spacetime have been proposed, which are the black-bounces metric (\cite{2019JCAP...02..042S,2021PhRvD.103h4052L}) and quantum deformed black hole (BH) (\cite{2021arXiv210202471B}). In present work, we investigate the rotating spacetime of these deformed Schwarzschild metric. They are exact solutions to the Einstein$'$s field equation. We analyzed the properties of these rotating spacetimes, such as event horizon (EH), stationary limit surface (SIS), structure of singularity ring, energy condition (EC), etc., and found that these rotating spacetime have some novel properties.

gr-qc↗

arXiv2021

The Possible Equation Of State Of Dark Matter in Low Surface Brightness Galaxies

The observed rotation curves of low surface brightness (LSB) galaxies play an essential role in studying dark matter, and indicate that there exists a central constant density dark matter core. However, the cosmological N-body simulations of cold dark matter predict an inner cusped halo with a power-law mass density distribution, and can't reproduce a central constant-density core. This phenomenon is called cusp-core problem. When dark matter is quiescent and satisfies the condition for hydrostatic equilibrium, using the equation of state can get the density profile in the static and spherically symmetric space-time. To solve the cusp-core problem, we assume that the equation of state is independent of the scaling transformation. Its lower order approximation for this type of equation of state can naturally lead to a special case, i.e. $p=ζρ+2εV_{rot}^{2}ρ$, where $p$ and $ρ$ are the pressure and density, $V_{rot}$ is the rotation velocity of galaxy, $ζ$ and $ ε$ are positive constants. It can obtain a density profile that is similar to the pseudo-isothermal halo model when $ε$ is around $0.15$. To get a more widely used model, let the equation of state include the polytropic model, i.e. $p= \fracζ{ρ_{0}^{s}}ρ^{1+s}+ 2εV_{rot}^{2}ρ$, we can get other kinds of density profiles, such as the profile that is nearly same with the Burkert profile, where $s$ and $ρ_{0}$ are positive constants.

astro-ph.GA↗

arXiv2020

The eccentricity enhancement effect of intermediate-mass-ratio-inspirals: dark matter and black hole mass

It was found that the dark matter (DM) in the intermediate-mass-ratio-inspiral (IMRI) system has a significant enhancement effect on the orbital eccentricity of the stellar massive compact object, such as a black hole (BH), which may be tested by space-based gravitational wave (GW) detectors including LISA, Taiji and Tianqin in future observations \citep{2019PhRvD.100d3013Y}. In this paper, we will study the enhancement effect of the eccentricity for an IMRI under different DM density profiles and center BH masses. Our results are as follows: $(1)$ in terms of the general DM spike distribution, the enhancement of the eccentricity is basically consistent with the power-law profile, which indicates that it is reasonable to adopt the power-law profile; $(2)$ in the presence of DM spike, the different masses of the center BH will affect the eccentricity, which provides a new way for us to detect the BH's mass; $(3)$ considering the change of the eccentricity in the presence and absence of DM spike, we find that it is possible to distinguish DM models by measuring the eccentricity at the scale of about $10^{5} GM/c^{2}$.

gr-qc↗

arXiv2019

Observational Constraints on the Rastall gravity from Rotation Curves of Low Surface Brightness Galaxies

The Rastall gravity is a modification of Einstein's general relativity, in which the energy-momentum conservation is not satisfied and depends on the gradient of the Ricci curvature. It is in dispute whether the Rastall gravity is equivalent to the general relativity (GR). In this work, we constrain the theory using the rotation curves of Low Surface Brightness (LSB) spiral galaxies. Through fitting the rotation curves of LSB galaxies, we obtain the parameter $β$ of the Rastall gravity. The $β$ values of LSB galaxies satisfy Weak Energy Condition (WEC) and Strong Energy Condition(SEC). Combining the $β$ values of type Ia supernovae and gravitational lensing of elliptical galaxies on the Rastall gravity, we conclude that the Rastall gravity is equivalent to the general relativity.

astro-ph.GA↗