Types Of Black Holes Research Articles

The Singularities of Gravitational Fields of Static Thin Loop and Double Spheres Reveal the Impossibility of Singularity Black Holes

In the classical Newtonian mechanics, the gravity fields of static thin loop and double spheres are two simple but foundational problems. However, in the Einstein’s theory of gravity, they are not simple. In fact, we do not know their solutions up to now. Based on the coordinate transformations of the Kerr and the Kerr-Newman solutions of the Einstein’s equation of gravity field with axial symmetry, the gravity fields of static thin loop and double spheres are obtained. The results indicate that, no matter how much the mass and density are, there are singularities at the central point of thin loop and the contact point of double spheres. What is more, the singularities are completely exposed in vacuum. Space near the surfaces of thin loop and spheres are highly curved, although the gravity fields are very weak. These results are inconsistent with practical experience and completely impossible. By reasonable analogy, black holes with singularity in cosmology and astrophysics are something illusive. Caused by the mathematical description of curved space-time, they do not exist in real world actually. If there are black holes in the universe, they can only be the types of the Newtonian black holes without singularities, rather than the Einstein’s singularity black holes. In order to escape the puzzle of singularity thoroughly, the description of gravity should return to the traditional form of dynamics in flat space. The renormalization of gravity and the unified description of four basic interactions may be possible only based on the frame of flat space-time. Otherwise, theses problems can not be solved forever. Physicists should have a clear understanding about this problem.

The Final Stage of Gravitationally Collapsed Thick Matter Layers

In the presence of aminimal length, physical objects cannot collapse to an infinite density, singular, matter point. In this paper, we consider the possible final stage of the gravitational collapse of “thick” matter layers. The energy momentum tensor we choose to model these shell-like objects is a proper modification of the source for “noncommutative geometry inspired,” regular black holes. By using higher momenta of Gaussian distribution to localize matter at finite distance from the origin, we obtain new solutions of the Einstein equation which smoothly interpolates between Minkowski’s geometry near the center of the shell and Schwarzschild’s spacetime far away from the matter layer. The metric is curvature singularity free. Black hole type solutions exist only for “heavy” shells; that is,M ≥Me, whereMeis the mass of the extremal configuration. We determine the Hawking temperature and a modified area law taking into account the extended nature of the source.

Change in entropy of non-spinning black holes w.r.t. the radius of event horizon in XRBs

The present research paper discusses the derivation for the change in entropy of Non- spinning black holes with respect to the change in the radius of event horizon applying the first law of black hole mechanics (\(\delta M = \frac{\kappa}{8\pi} \delta A + \varOmega\delta J - \upsilon\delta Q\)) with the relation for the change in entropy δS=8πMδM. When the work is further extended with proper operation, the entropy of black hole is obtained almost the same as the Bekenstein-Hawking entropy of black hole. This is the entirely new method to obtain the change in entropy of Non-spinning black holes w.r.t. the radius of event horizon and Hawking entropy of black hole. We have also calculated their values for different types of test non-spinning black holes having masses 5–20M⊙ found in X-ray binaries (Narayan, gr-qc/0506078v1, 2005).

Fundamental properties of Fanaroff-Riley type II radio galaxies investigated via Monte Carlo simulations

[Abridged] Radio galaxies and quasars are among the largest and most powerful single objects known and are believed to have had a significant impact on the evolving Universe and its large scale structure. We explore the intrinsic and extrinsic properties of the population of FRII objects (kinetic luminosities, lifetimes, and the central densities of their environments). In particular, the radio and kinetic luminosity functions of FRIIs are investigated using the complete, flux limited radio catalogues of 3CRR and Best et al. We construct multidimensional Monte Carlo simulations using semi-analytical models of FRII radio source growth to create artificial samples of radio galaxies. Unlike previous studies, we compare radio luminosity functions found with both the observed and simulated data to explore the fundamental source parameters. We allow the source physical properties to co-evolve with redshift, and we find that all the investigated parameters most likely undergo cosmological evolution. Strikingly, we find that the break in the kinetic luminosity function must undergo redshift evolution of at least (1+z)^3. The fundamental parameters are strongly degenerate, and independent constraints are necessary to draw more precise conclusions. We use the estimated kinetic luminosity functions to set constraints on the duty cycles of these powerful radio sources. A comparison of the duty cycles of powerful FRIIs with those determined from radiative luminosities of AGN of comparable black hole mass suggests a transition in behaviour from high to low redshifts, corresponding to either a drop in the typical black hole mass of powerful FRIIs at low redshifts, or a transition to a kinetically-dominated, radiatively-inefficient FRII population.

Black hole for the Einstein-Chern-Simons gravity

We consider a 5-dimensional action which is composed of a gravitational sector and a sector of matter, where the gravitational sector is given by a Einstein-Chern-Simons gravity action instead of the Einstein-Hilbert action. We obtain the Einstein-Chern-Simons (EChS) field equations together with its spherically sym- metric solution, which leads, in certain limit, to the standard five dimensional solution of the Einstein-Cartan field equations. It is found the conditions under which the EChS field equations admits black hole type solutions. The maximal extension and conformal compactification are also studied

On asymptotically AdS-like solutions of three dimensional massive gravity

In this paper we have added Maxwell, Maxwell-Chern-Simons and gravitational Chern-Simons terms to Born-Infeld extended new massive gravity and we have found different types of (non)extremal charged black holes. For each black hole we find mass, angular momentum, entropy and temperature. Since our solutions are asymptotically AdS or warped-AdS, we infer central charges of dual CFTs by using Cardy's formula. Computing conserved charges associated to asymptotic symmetry transformations confirms calculation of central charges. For CFTs dual to asymptotically AdS solutions we find left central charges from Cardy's formula, while conserved charge approach gives both left and right central charges. For CFTs dual to asymptotically warped-AdS solutions, left and right central charges are equal when we have Maxwell-Chern-Simons term but they have different values when gravitational Chern-Simons term is included.

Gamma-ray constraints on the first stars from annihilation of light WIMPs

We calculate the limits on the fraction of viable dark matter minihalos in the early universe to host Population III.1 stars, surviving today as dark matter spikes in our Milky Way halo. Motivated by potential hints of light dark matter from the DAMA and CoGeNT direct dark matter searches, we consider thermal relic WIMP dark matter with masses of 5, 10, and 20 GeV, and annihilation to ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$, and $q\overline{q}$. From this brief study we conclude that, if dark matter is light, either the typical black hole size is $\ensuremath{\lesssim}100{M}_{\ensuremath{\bigodot}}$ (i.e. there is no significant Dark Star phase), and/or dark matter annihilates primarily to ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ or other final states that result in low gamma-ray luminosity, and/or that an extremely small fraction of minihalos in the early universe that seem suitable to host the formation of the first stars actually did.

Spherical Symmetric Dyonic Black Holes and Vacuum Geometries in 4 D N=1 Supergravity on Kähler-ricci Soliton

In this paper we consider several aspects of dyonic non-supersymmetric black holes in fourdimensional N = 1 supergravity coupled to chiral and vector multiplets. The scalar manifold can be considered as a one-parameter family of Kähler manifolds generated by a Kähler–Ricci flow equation. This setup implies that we have a family of dyonic non-supersymmetric black holes deformed with respect to the flow parameter related to the Kähler–Ricci soliton, which possibly controls the nature of black holes, such as their asymptotic and near horizon geometries. We mainly consider two types of black holes, namely a family of dyonic Reissner–Nordströmlike black holes and Bertotti–Robinson-like black holes where the scalars are freezing all over spacetime and at the horizon, respectively. In addition, the corresponding vacuum structures for such black holes are also discussed in the context of Morse–(Bott) theory. Finally, we give some simple CPn-models whose superpotential and gauge couplings have a linear form.

Can the Reissner-Nordström black hole or Schwarzschild black hole be the stable Planck-scale particle accelerator?

It is shown that the extremal Reissner-Nordstr\"{o}m black hole, the non-extremal one with multiple scattering particles, and the Schwarzschild black hole with radial head-on particles are stable under the collision of the particles near the horizon, if the back-reaction effect and the effect generated by gravity of particles are involved. Moreover, the collision near Reissner-Nordstr\"{o}m black holes with astrophysically typical mass can not generate the Planck-scale center-of-mass energy. However, the head-on collision near the typical primordial black hole could just occur at the Planck-energy scale.

Neutrino trapping in braneworld extremely compact stars

Extremely Compact Stars (ECS) contain trapped null geodesics. When such objects enter the evolution period admitting geodetical motion of neutrinos, certain part of neutrinos produced in their interior will be trapped influencing their neutrino luminosity and thermal evolution. We study neutrino trapping in the braneworld ECS, assuming uniform distribution of neutrino emissivity and massless neutrinos. We give the efficiency of the neutrino trapping effects in the framework of the simple model of the internal spacetime with uniform distribution of energy density, and external spacetime described by the Reissner-Nordström geometry characterized by the braneworld “tidal” parameter b. For b < 0 the external spacetime is of the black-hole type, while for b > 0 the external spacetime can be of both black-hole and naked-singularity type. Then the ECS surface radius R can be located also above the unstable (outer) photon circular orbit. Such basically new types of the spacetimes strongly alter the trapping phenomena as compared to the standard case of b = 0. It is shown that the neutrino trapping effects are slightly lowered by the presence of physically more plausible case of b < 0, as compared to the standard internal Schwarzschild spacetime, while they can be magnified by positive tidal charges if b < 1 and lowered for b > 1. However, potential astrophysical relevance of the trapping phenomena is strongly enhanced for negative tidal charges enabling a significant enlargement of the ECS surface radius to values coherent with recent observations.

Photon and neutrino redshift in the field of braneworld compact stars

We study gravitational redshift of photons and neutrinos radiated by the braneworld neutron or quark stars that are considered in the framework of the simple model of the internal spacetime with uniform distribution of energy density, and the external spacetime described by the Reissner-Nordström geometry characterized by the braneworld ``tidal'' charge b. For negative tidal charges, the external spacetime is of the black-hole type, while for positive tidal charges, the external spacetime can be of both black-hole and naked-singularity type. We consider also extremely compact stars allowing existence of trapped null geodesics in their interior. We assume radiation of photons from the surface at radius R, neutrinos from the whole compact star interior, and their motion along radial null geodesics of the spacetime. In dependency on the compact stars parameters b and R, the photon surface redshift is related to the range of the neutrino internal redshift and the signatures of the tidal charge and possible existence of extremely compact stars are discussed. When both surface (photon) and internal (neutrino) redshift are given by observations, both compact star parameters R and b can be determined in the framework of our simple model.

Black holes in Born-Infeld extended new massive gravity

In this paper we find different types of black holes for the Born-Infeld extended new massive gravity. Our solutions include (un)charged warped (A)dS black holes for four and six derivative expanded action. We also look at the black holes in unexpanded BI action. In each case we calculate the entropy, angular momentum and mass of the black holes. We also find the central charges for the CFT duals.

TypeDsolutions of 3D new massive gravity

In a recent reformulation of three-dimensional new massive gravity (NMG), the field equations of the theory consist of a massive (tensorial) Klein-Gordon type equation with a curvature-squared source term and a constraint equation. Using this framework, we present all algebraic type D solutions of NMG with constant and nonconstant scalar curvatures. For constant scalar curvature, they include homogeneous anisotropic solutions which encompass both solutions originating from topologically massive gravity (TMG), Bianchi types II, VIII, IX, and those of non-TMG origin, Bianchi types VI_{0} and VII_{0} . For a special relation between the cosmological and mass parameters, \lambda=m^2, they also include conformally flat solutions, and in particular those being locally isometric to the previously-known Kaluza-Klein type AdS_2xS^1 or dS_2x S^1 solutions. For nonconstant scalar curvature, all the solutions are conformally flat and exist only for \lambda=m^2 . We find two general metrics which possess at least one Killing vector and comprise all such solutions. We also discuss some properties of these solutions, delineating among them black hole type solutions.

Influence of Gauss-Bonnet Coupling Parameter on the Thermodynamic Properties of Einstein-Gauss-Bonnet and Einstein-Yang-Mills-Gauss-Bonnet Black Holes

This paper deals in the thermodynamic properties of Einstein-Gauss-Bonnet and Einstein-Yang-Mills-Gauss-Bonnet black holes. It exhibits the various stable and unstable phases of the black holes in these two modified gravity theories. In the first section, that reveals the various aspects of Einstein-Gauss-Bonnet black holes, we chose to study the changes in the Hawking Temperature with variations in the radius of event horizon (r) and charge (Q); and tried to justify them physically. Secondly in case of Einstein-Yang-Mills-Gauss-Bonnet black holes, we have attempted to compare the changes in the various thermodynamic parameters with varying r and Q; with the Einstein-Gauss-Bonnet black holes at a macroscopic level. Here we have considered the Yang Mills tensor, electromagnetic Lagrangian added to the action integrand. Again this very work deals in drawing out the similarities between these two types of black holes, thereby throwing some light on the aspect of black hole stability. Later we have also introspected the effects of the Gauss-Bonnet coupling parameter α, whose function (6αr), is added as a correction term to the black hole entropy. We have especially focused on what changes does it have upon the nature of the plots as to whether it enhances or reduces the effect of Q on the behavior of the curves. Finally this paper has also kept an eye at estimating the stability domains of the black holes described in these two gravity theories.

Accretion of Chaplygin gas upon black holes: formation of faster outflowing winds

We study the accretion of modified Chaplygin gas upon different types of black holes. Modified Chaplygin gas is one of the best candidates for a combined model of dark matter and dark energy. In addition, from a field theoretical point of view the modified Chaplygin gas model is equivalent to that of a scalar field having a self-interacting potential. We formulate the equations related to both spherical accretion and disc accretion, and respective winds. The corresponding numerical solutions of the flow, particularly of velocity, are presented and analysed. We show that the accretion–wind system of modified Chaplygin gas dramatically alters the wind solutions, producing faster winds, upon changes in physical parameters, while accretion solutions qualitatively remain unaffected. This implies that modified Chaplygin gas is more prone to produce outflow which is the natural consequence of the dark energy into the system.

Number and entropy of halo black holes

Based on constraints from microlensing and disk stability, both with and without limitations from wide binary surveys, we estimate the total number and entropy of intermediate mass black holes. Given the visible universe comprises 10 11 halos each of mass ∼10 12 M ⊙, typical core black holes of mean mass ∼10 7 M ⊙ set the dimensionless entropy ( S/ k) of the universe at a thousand googols. Identification of all dark matter as black holes sets the dimensionless entropy of the universe at 10 million googols, implying that dark matter can contribute over 99% of entropy, which favors all dark matter as black holes in the mass regime of ∼10 5 M ⊙.

Hawking temperature and thermodynamics geometry of the 3D charged-dilaton black holes

In this Letter, we first investigate the Hawking temperature of the 3D charged-dilaton black holes by using the Generalized Uncertainty Principle. The results show that corresponding to the minimum radius of the event horizon, with the order of the Planck scale, there is a minimum mass or remnant for this type of black holes. Then, we study the thermodynamics geometry of the 3D charged-dilaton black holes. We find that the Weinhold geometry of the 3D charged-dilaton black holes is curved, whereas its Ruppeiner geometry is flat. Finally, we calculate the heat capacity of the black holes, and obtain the phase transition point.

Hawking radiation of the fermionic field and anomaly in (2+1)-dimensional black holes

The method of anomaly cancellation to derive Hawking radiation initiated by Robinson and Wilczek is applied to (2+1)-dimensional stationary black holes. Using the dimensional reduction technique, we find that the near-horizon physics for the fermionic field in the background of the general (2+1)-dimensional stationary black hole can be approximated by an infinite collection of two-component fermionic fields in the (1+1)-dimensional spacetime background coupled with the dilaton field and U(1) gauge field. By restoring the gauge invariance and the general coordinate covariance for the reduced two-dimensional theory, the Hawking flux and temperature of a black hole are obtained. We apply this method to two types of black holes in three-dimensional spacetime, which are the BTZ black hole in Einstein gravity and a rotating black hole in Bergshoeff–Hohm–Townsend massive gravity.

SPHERICALLY SYMMETRIC AND ROTATING WORMHOLES PRODUCED BY LIGHTLIKE BRANES

Lightlike p-branes (LL-branes) with dynamical (variable) tension allow simple and elegant Polyakov-type and dual to it Nambu–Goto-like worldvolume action formulations. Here we first briefly describe the dynamics of LL-branes as test objects in various physically interesting gravitational backgrounds of black hole type, including rotating ones. Next we show that LL-branes are the appropriate gravitational sources that provide proper matter energy–momentum tensors in the Einstein equations of motion needed to generate traversable wormhole solutions, in particular, self-consistent cylindrical rotating wormholes, with the LL-branes occupying their throats. Here a major role is being played by the dynamical LL-brane tension which turns out to be negative but may be of arbitrary small magnitude. As a particular solution we obtain traversable wormhole with Schwarzschild geometry generated by a LL-brane positioned at the wormhole throat, which represents the correct consistent realization of the original Einstein–Rosen "bridge" manifold.

Arithmetic of $ \mathcal{N} = 8 $ black holes

The microscopic formula for the degeneracies of 1/8 BPS black holes in type II string theory compactified on a six dimensional torus can be expressed as a sum of several terms. One of the terms is a function of the Cremmer-Julia invariant and gives the leading contribution to the entropy in the large charge limit. The other terms, which give exponentially subleading contribution, depend not only on the Cremmer-Julia invariant, but also on the arithmetic properties of the charges, and in fact exist only when the charges satisfy special arithmetic properties. We identify the origin of these terms in the macroscopic formula for the black hole entropy, based on quantum entropy function, as the contribution from non-trivial saddle point(s) in the path integral of string theory over the near horizon geometry. These saddle points exist only when the charge vectors satisfy the arithmetic properties required for the corresponding term in the microscopic formula to exist. Furthermore the leading contribution from these saddle points in the large charge limit agrees with the leading asymptotic behaviour of the corresponding term in the degeneracy formula.