Types Of Black Holes Research Articles

Astrophysical and electromagnetic emissivity properties of black holes surrounded by a quintessence type exotic fluid in the scalar–vector–tensor modified gravity

The astrophysical consequences of the presence of a quintessence scalar field on the evolution of the horizon and on the accretion disk surrounding a static black hole, in the scalar–vector–tensor version of modified gravity (MOG), are investigated. The positions of the stable circular orbits of the massive test particles, moving around the central object, are obtained from the extremum of the effective potential. Detailed calculations are also presented to investigate the light deflection, shadow and Shapiro effect for such a black hole. The electromagnetic properties of the accretion disks that form around such black holes are considered in detail. The energy flux and efficiency parameter are estimated analytically and numerically. A comparison with the disk properties in Schwarzschild geometry is also performed. The quantum properties of the black hole are also considered, and the Hawking temperature and the mass loss rate due to the Hawking radiation are considered. The obtained results may lead to the possibility of direct astrophysical tests of black hole type objects in modified gravity theories.

Gravito-electromagnetic perturbations and QNMs of regular black holes

In the framework of Einstein’s gravity coupled to nonlinear electromagnetic fields, we study gravito-electromagnetic perturbations of magnetic regular black holes (BHs). The master equations of perturbations are obtained through Chandrasekhar’s formulation, from which it can be seen, different from the electric counterparts, for magnetic BHs gravitational perturbations with odd-parity coupled only to the electromagnetic perturbations with even-parity. We solve the master equations numerically and obtain quasinormal modes (QNMs) for three typical regular BHs. Results show that QNMs of distinct regular BHs differ significantly, and they differ from that of the Reissner–Nordström BH as well. Indications of these results on the stability of these regular BHs are discussed in detail.

Reduced Kiselev black hole

The Kiselev model describes a black hole surrounded by a fluid with equations of state p_r/rho =-1 and p_t/rho =(3w+1)/2 respectively in radial and tangential directions. It has been extensively studied in the parameter region -1<w<-1/3. If one rids off the black hole and turns to the region -1/3<w<0, i.e. p_t>0, then a new horizon of black hole type will emerge. This case has been mentioned in Kiselev’s pioneer work but seldom investigated in the literature. Referring to it as reduced Kiselev black hole, we revisit this case with attention to its causal structure, thermodynamics, shadow cast and weak-field limit. An alternative interpretation and extensions of the black hole are also discussed.

Types and State-of-art Detection Paradigms of Black Holes

Contemporarily, mankind has been exploring the universe for a long time, as early as 1609 when Galileo started to observe the closer planets with telescopes. The universe has an indispensable and extremely important object of study, which is the black hole, a celestial body whose curvature of space-time reaches the point where light cannot escape. The paper selects black holes as the investigation target discussing from the following aspects. Primarily, the basic description of black holes will be given. Then, we present several characteristics and several types of black holes and explain their importance in the universe Subsequently, detection paradigms for the black holes will be discussed and analyzed. The significance of our study is to reflect the efforts and efforts of human beings in exploring the universe, and to study the mysterious object of black holes. According to the analysis, it is believed that in the future, after several generations of efforts and exploration, and the upgrade of technology, human beings will have a deeper understanding of the universe and the secrets of black holes will no longer exist. These results shed light on guiding further exploration regarding to black holes.

Astrophysical observables for regular black holes with sub-Planckian curvature* *Supported in part by the Natural Science Foundation of China (11875053, 12035016). It is also supported by the Beijing Natural Science Foundation (1222031), and the Sichuan Youth Science and Technology Innovation Research Team with (21CXTD0038), Central Government Funds of Guiding Local Scientific and Technological Development for Sichuan Province with (2021ZYD0032)

We investigate the photon sphere and marginally stable circular orbit of massive particles over the recently proposed regular black holes with sub-Planckian curvature and a Minkowskian core. We derive the effective potential for geodesic orbits and determine the radius of circular photon orbits, with an analysis of the stability of these orbits. We extend our analysis to the background of a compact massive object (CMO) without a horizon, whose mass is below the lowest bound for the formation of a black hole. For massive particles, marginally stable circular orbits become double-valued in the CMO phase. Through a comparison with Bardeen and Hayward black holes, we also find that the locations of the photon sphere and marginally stable circular orbit in the CMO phase with a Minkowskian core are evidently different from those in the CMO phase with a dS core, which potentially provides a way to distinguish between these two types of black holes by astronomical observation. Finally, we present the observational constraint on the deviation parameter for such regular black holes using observed data from the black hole M87*.

Entropy of black holes coupled to a scalar field

The Hamiltonian approach to black hole entropy, recently proposed in the framework of Poincar\'e gauge theory, is extended by including the scalar matter. The improved approach is used to analyse asymptotic charges and entropy of a typical black hole with scalar hair in two complementary dynamical settings, in GR and in the teleparallel gravity. In both cases, the results confirm the validity of the first law.

Numerical stochastic inflation constrained by frozen noise

Stochastic inflation can resolve strong inflationary perturbations, which seed primordial black holes. I present a fast and accurate way to compute these perturbations in typical black hole producing single-field models, treating the short-wavelength Fourier modes beyond the de Sitter approximation. The squeezing and freezing of the modes reduces the problem to one dimension, and the resulting new form of the stochastic equations, dubbed `constrained stochastic inflation,' can be solved efficiently with semi-analytical techniques and numerical importance sampling. In an example case, the perturbation distribution is resolved in seconds deep into its non-Gaussian tail, a speed-up of factor 109 compared to a previous study. Along the way, I comment on the role of the momentum constraint in stochastic inflation.

Comparison of Different Types of Black Holes

With the deeper exploration on black hole, more and more categories of black holes are defined by astronomers and physicists. The article will discuss the differences in detection and process of accretion between the binary black holes and isolated black holes through analysing previous researches on black holes. To search for binary black holes, whose companion may be luminous, classical methods include spectrum test and calculation of the operation of binary star system are applied. On the other hand, the state-or-art facilities HST are used to detect them based on gravitational lens effect. These two different sorts of black holes also have their unique process of accretion. The binary black holes absorb particles from the stellar wind which is given out by their companion, forming two “minidisk”. The process is accompanied with strong emission of X-ray. Meanwhile, the accretion of isolated black hole forms only one ring of gas. The accretion flow is mostly weak and radioactively inefficient. The reason for these differences can be their separate optical features and relationships with environment. It is aimed at distinguishing the two kinds of black holes with different framework, making them easier to identify only with optical evidence or data on radioactive emission. Therefore, it’s easy to tell the infer structure from evidence that astronomers can comparatively easier obtain about black holes, which is beneficial for further studies about black holes internal structure details. These results shed light on guiding further exploration of black holes.

Equations-of-state deduced form different types of black holes

Black holes are seen as thermodynamical systems. They can be characterized by thermodynamic intensive quantities such as temperature, pressure, and extensive quantities such as entropy and energy density. In this paper, we focus on the thermodynamical properties of (a) Schwarzschild, (b) Reissner–Nordström, (c) Kerr, and (d) Kerr–Newman black holes. These allow to estimate the corresponding equations-of-state (EoS) and the squared speed of sound for each of them. The latter helps to calculate the ratio of the bulk viscosity to the shear viscosity for each of the black holes. We conclude that the resulting EoS enhances when moving from Schwarzschild to Reissner–Nordström to Kerr, and to Kerr–Newman black holes.

Renormalization group flow to effective quantum mechanics in the IR in an emergent dual holographic description for spontaneous chiral symmetry breaking

Implementing the Wilsonian renormalization group (RG) transformation in a nonperturbative way, we construct an effective holographic dual description with an emergent extradimension identified with an RG scale. Taking the large$-N$ limit, we obtain an equation of motion of an order-parameter field, here the chiral condensate for our explicit demonstration. In particular, an intertwined structure manifests between the first-order RG flow equations of renormalized coupling functions and the second-order differential equation of the order-parameter field, thus referred to as a nonperturbative RG-improved mean-field theory. Assuming translational symmetry as a vacuum state, we solve these nonlinear coupled mean-field equations based on a matching method between UV- and IR-regional solutions. As a result, we find an RG flow from a weakly-coupled chiral-symmetric UV fixed point to a strongly-correlated chiral-symmetry broken IR fixed point, where the renormalized velocity of Dirac fermions vanishes most rapidly and effective quantum mechanics appears at IR. Furthermore, we translate these RG flows of coupling functions into those of emergent metric tensors and extract out geometrical properties of the emergent holographic spacetime constructed from the UV- and IR-regional solutions. Surprisingly, we obtain the volume law of entanglement entropy in the Ryu-Takayanagi formula, which implies appearance of a black hole type solution in the limit of infinite cutoff even at zero temperature. We critically discuss our field theoretic interpretation for this solution in terms of potentially gapless multi-particle excitation spectra.

Algorithms and radiation dynamics for the vicinity of black holes

We present the results of our studies on accretion disks in the proximity of astrophysical black holes. These disks can be of varying degrees of opacity, geometrical shapes, sizes, and volumes. The central compact object is a Schwarzschild or a Kerr black hole of various spin parameters. We describe the environment and the physics of the systems under examination and the disk models considered. We first investigate the effects of the spacetime rotation on photon trajectories. We then examine the radiation forces recorded at various points of the arrangement inside and outside the disk material, and in the inner, outer, and off-equatorial material orbits. We document and explore the radiation effects, which are revealed to be significant and positively consequential. Afterward, we inspect the possible imaging outcome of various types of black hole and accretion disk configurations, and we show our results for plots that could be used to estimate the central black hole spin in a system. Finally, we show results regarding the disk material orbit degradation due to its thermal radiation.

Sonic black hole duct

The sonic black hole is a type of acoustic black hole that attenuates sound propagation via the acoustic black hole effect. This phenomenon is when an incident acoustic wave propagates through a power-law tapering geometry causing the wavelength to compress, the wave speed to decrease, and the time for the wave packet to reach the exit to extend infinitely. As a result, the wave never reaches the exit, so it cannot be reflected or transmitted. However, this outcome relies on the taper approaching exactly zero, which is impossible to manufacture. Therefore, the taper must be truncated leading to imperfect sound absorption. One method to increase the sound absorption is by applying perforations to the rings. This study explores the effect that varying the perforations on the sonic black hole’s rings has on the absorption coefficient from 1 to 5 kHz.

Parameter estimation of eccentric gravitational waves with a decihertz observatory and its cosmological implications

Eccentricity of compact binaries can improve the parameter estimation of gravitational waves (GWs), which is due to the fact that the multiple harmonics induced by eccentricity can provide more information and break the degeneracy between waveform parameters. In this paper, we first investigate the parameter estimation of eccentric GWs with decihertz observatory. We consider two scenarios for the configuration of DECIGO, i.e., the one cluster of DECIGO with its design sensitivity and B-DECIGO which also has one cluster but with inferior sensitivity as a comparison. We adopt the Fisher matrix to estimate the parameter errors. By mocking up the typical binaries in GWTC-3, we find a nonvanishing eccentricity can significantly improve the estimation for almost all waveform parameters. In particular, the localization of typical binary black holes (BBH) can achieve $\mathcal{O}(10--{10}^{3.5})$ factors of improvement when the initial eccentricity ${e}_{0}=0.4$ at 0.1 Hz. The precise localization of binary neutron stars (BNS) and neutron star--black hole binaries (NSBH), together with the large improvement of localization of BBH from eccentricity in the midband, inspire us to construct the catalogs of golden dark sirens whose host galaxies can be uniquely identified. We find that with only one cluster of DECIGO running 1 year in its design sensitivity, hundreds of golden dark BNS, NSBH, and tens of golden dark BBH can be observed. Eccentricity can greatly increase the population of golden dark BBH from $\ensuremath{\sim}7({e}_{0}=0)$ to $\ensuremath{\sim}65({e}_{0}=0.2)$. Such an increase of population of golden dark BBH events can improve the precision of Hubble constant measurement from 2.06% to 0.68%, matter density parameter from 64% to 16% in $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Through the phenomenological parametrization of GW propagation, the constraints of modified gravity can be improved from 6.2% to 1.6%. Our results show the remarkable significance of eccentricity for the detection and parameter estimation of GW events, allowing us to probe the Universe precisely.

The State-of-art Theorem and Detection Paradigms of Black Holes

The black hole has been a mystery and a source of detection motivation for the human race ever since our quest of the discovery and research of other space. In general, the black hole can be defined as a special time-space structure where the gravity is strong enough to trap the photons, i.e., the light will be unable to penetrate or escape from it. In this paper, the current theorem and state-of-art detection paradigms are discussed in detail. Primarily, the categories of the black holes are demonstrated. The four different types of black holes all present their unique features. the quest for black hole exploration has never ceased. It has achieved stunning breakthrough with the first ever photo taken of the black hole by NASA in 2019. The future analysis of black hole excavation and research has been brought a bright future, as technology and outer space exploration plans continue to evolve. These results shed light on guiding further exploration of cosmology as well as the astrophysics.

The Application of the Hybrid Projection Method for the Analysis

The problem of scattering of a plane electromagnetic wave by a 2D periodic structure formed by absorbing spherical radially inhomogeneous dielectric elements is considered. The elements have the type of electromagnetic black holes located on a semi-infinite substrate. The numerical algorithm of the solution is developed. The algorithm is based on the hybrid projection method and takes into account the peculiarities of the black hole construction. The algorithm is generalized to the case, when black holes are situated on aperfectly conducting screen. New expressions for calculating the power absorbed by the structure elements are derived. The numerical results characterizing the efficiency of the structure absorption are presented.

Application of the Hybrid Projection Method for Analysis of Absorbing Periodic Structures with Spherical Elements of Electromagnetic Black Hole Type

Application of the Hybrid Projection Method for Analysis of Absorbing Periodic Structures with Spherical Elements of Electromagnetic Black Hole Type

Black Holes with Electric and Magnetic Charges in F(R)$F(R)$ Gravity

AbstractWe construct spherically symmetric and static solutions in gravity coupled with electromagnetic fields. The solutions include new types of black holes with electric and magnetic charges. We show that the higher‐derivative terms make the curvature singularity much softer than that in the charged black holes in Einstein's general relativity. We calculate some thermodynamical quantities of the obtained black holes like entropy, Hawking radiation, and quasi‐local energy and we confirm that the black hole solutions satisfy the first law of thermodynamics. Finally, we study the stability analysis using the odd‐type mode and show that there are stable black hole solutions and the radial speed of the parity‐odd mode is unit, that is, the speed of light.

Eccentricity of Long Inspiraling Compact Binaries Sheds Light on Dark Sirens

The localization and distance inference of gravitational waves are two crucial factors for dark sirens as precise probes of cosmology, astrophysics, and fundamental physics. In this Letter, for the first time we investigate the parameter estimation of gravitational waves emitted by the eccentric compact binaries in the midfrequency (0.1-10Hz) band. Based on the configuration of one cluster of DECIGO (B-DECIGO), we simulate five types of typical compact binaries in GWTC-3 with component mass ranging from O(1∼100) M_{⊙}. For each type of binaries, we assign discrete eccentricities from 0 to 0.4 at 0.1Hz in 10^{3} random orientations. The multiple harmonics induced by eccentricity can break the degeneracy between parameters. We find that with eccentricity e_{0}=0.4, these typical binaries can achieve O(10^{2}-10^{4}) improvement for the distance inference in the near face-on orientations, compared to the circular case. More importantly, a nonvanishing eccentricity (0.01-0.4) can significantly improve the source localization of the typical binary black holes, most by 1.5-3.5 orders of magnitude. Our result shows the remarkable significance of eccentricity for dark sirens in the midband as precise probes of the Universe.

Binary mergers in bootstrapped Newtonian gravity: Mass gap and black hole area law

We study binary mergers in bootstrapped Newtonian gravity, where higher-order couplings are added to the non-relativistic Lagrangian for the Newtonian potential. In this theory, the Arnowitt-Deser-Misner (ADM) mass differs from both the proper mass of Newtonian gravity and the proper mass of general relativity, which affects the interpretation of astrophysical and cosmological events. The aforementioned difference particularly provides important phenomenological constraints for the mass of the emitted matter and the compactness of the final object after the merger. The interpretation of the GW150914 signal in this theory also shows that LIGO's findings do not violate the mass gap, contrary to usual claims. We indeed find that typical stellar black hole masses can fit LIGO's data for a considerable range of compactness values. We calculate the black hole entropy in this context, which leads to a generalised black hole area law. Non-linear effects are found to effectively change only the gravitational strength via the renormalisation of Newton's constant in this case.

Tidal effects of a dark matter halo around a galactic black hole* *Supported by the National Natural Science Foundation of China (11875026, 11875025, 12035005, 2020YFC2201400)

We investigate tidal forces and geodesic deviation motion in the spacetime of a black hole in a galaxy with a dark matter halo. Our results show that tidal forces and geodesic deviation motion depend on the mass of the dark matter halo and the typical lengthscale of the galaxy. The effect of the typical lengthscale of the galaxy on the tidal force is opposite to that of dark matter mass. With increasing dark matter mass, the radial tidal force increases in the region far from the black hole but decreases in the region near the black hole. Furthermore, the absolute value of angular tidal force monotonously increases with the dark matter halo mass. The angular tidal force also depends on the particle energy, and the effects of dark matter become more distinct for the test particle at higher energies, which differs from the behavior observed in typical static black hole spacetimes. We also present the change in the geodesic deviation vector with dark matter halo mass and the typical lengthscale of a galaxy under two types of initial conditions.