Types Of Black Holes Research Articles

Fate of chaotic binaries

A typical stellar mass black hole with a lighter companion is shown to succumb to a chaotic precession of the orbital plane. As a result, the optimal candidates for the direct detection of gravitational waves by Earth based interferometers can show irregular modulation of the waveform during the last orbits before plunge. The precession and the subsequent modulation of the gravitational radiation depends on the mass ratio, eccentricity, and spins. The smaller the mass of the companion, the more prominent the effect of the precession. The most important parameters are the spin magnitudes and misalignments. If the spins are small and nearly aligned with the orbital angular momentum, then there will be no chaotic precession while increasing both the spin magnitudes and misalignments increases the erratic precession. A large eccentricity can be induced by large, misaligned spins but does not seem to be required for chaos. An irregular precession of the orbital plane will generate irregularities in the gravitational wave frequency but may have a lesser effect on the total number of cycles observed.

Strong gravitational lensing: Why no central black holes?

We investigate how central black holes (BHs) inhabited in galactic dark halos could affect strong gravitational lensing. The distribution of integral lensing probability with image separations are calculated for quasars of redshift 1.5 by foreground dark matter halos. The mass density of dark halos is taken to be the Navarro-Frenk-White (NFW) profile such that, when the mass of a halo is less than $10^{14} M_{\sun}$, its central black holes or a bulge is included as a point mass. The relationship between the masses $M_{\bullet}$ of supermassive black holes and the total gravitational mass $M_{\mathrm{DM}}$ of their host galaxy is adopted from the most recent literature. Only a flat $\Lambda$CDM model is considered here. It is shown that, while a single black hole for each galaxy contributes considerable but not sufficient lensing probabilities at small image separations compared with those without black holes, the bulges (which are about 100--1000 times larger in mass than a typical black hole) would definitely contribute enough probabilities at small image separations, although it gives too high probabilities at large separation angles compared with lensing observations.

Gravitational lensing in the strong field limit

We provide an analytic method to discriminate among different types of black holes on the ground of their strong field gravitational lensing properties. We expand the deflection angle of the photon in the neighbourhood of complete capture, defining a strong field limit, in opposition to the standard weak field limit. This expansion is worked out for a completely generic spherically symmetric spacetime, without any reference to the field equations and just assuming that the light ray follows the geodesics equation. We prove that the deflection angle always diverges logarithmically when the minimum impact parameter is reached. We apply this general formalism to Schwarzschild, Reissner-Nordstrom and Janis-Newman-Winicour black holes. We then compare the coefficients characterizing these metrics and find that different collapsed objects are characterized by different strong field limits. The strong field limit coefficients are directly connected to the observables, such as the position and the magnification of the relativistic images. As a concrete example, we consider the black hole at the centre of our galaxy and estimate the optical resolution needed to investigate its strong field behaviour through its relativistic images.

New type of regular black holes and particlelike solutions from nonlinear electrodynamics

We show that the Bronnikov theorem on the nonexistence of regular electrically charged black holes can be circumvented. In the frame of nonlinear electrodynamics, we present the exact regular black hole solutions of a hybrid type. They are electrically charged, but contain a `dual' core confining a polarization of magnetic charges. The considered example is based on a modification of the Ay\'on-Beato & Garc\'\i a solution. It represents a very specific realization of the idea on confinement based on dual electrodynamics and dual superconductivity.

Gravitation with superposed Gauss-Bonnet terms in higher dimensions: Black hole metrics and maximal extensions

Our starting point is an iterative construction suited to combinatorics in arbitarary dimensions d, of totally anisymmetrized p-Riemann $2p$ forms $(2p<~d)$ generalizing the $(1\ensuremath{-})$Riemann curvature $2$-forms. The superposition of p-Ricci scalars obtained from the p-Riemann forms defines the maximally Gauss-Bonnet extended gravitational Lagrangian. Metrics, spherically symmetric in $(d\ensuremath{-}1)$ space dimensions, are constructed for the general case. The problem is directly reduced to solving polynomial equations. For some black-hole type metrics the horizons are obtained by solving polynomial equations. Corresponding Kruskal-type maximal extensions are obtained explicitly in complete generality, as is also the periodicity of time for the Euclidean signature. We show how to include a cosmological constant and a point charge. Possible further developments and applications are indicated.

T-Duality of Axial and Vector Dyonic Integrable Models

A general construction of affine nonabelian (NA)-Toda models in terms of the axial and vector gauged two loop WZNW model is discussed. They represent integrable perturbations of the conformal σ-models (with tachyons included) describing (charged) black hole type string backgrounds. We study the off-critical T-duality between certain families of axial and vector type integrable models for the case of affine NA-Toda theories with one global U(1) symmetry. In particular we find the Lie algebraic condition defining a subclass of T-selfdual torsionless NA-Toda models and their zero curvature representation.

Massless scalar fields and topological black holes

The exact static solutions in the higher dimensional Einstein-Maxwell-Klein-Gordon theory are investigated. With the help of the methods developed for the effective dilaton type gauge gravity models in two dimensions, we find new spherically and hyperbolically symmetric solutions which generalize the four dimensional configurations of Dereli and Eri\ifmmode \mbox{\c{s}}\else \c{s}\fi{}. We show that, like in four dimensions, the nontrivial scalar field yields, in general, a naked singularity. The new solutions are compared with the higher dimensional Brans-Dicke black hole type solutions.

Einstein-Proca model: spherically symmetric solutions

The Proca wave equation describes a classical massive spin 1 particle. We analyze the gravitational interaction of this vector field. In particular, the spherically symmetric solutions of the Einstein-Proca coupled system are obtained numerically. Although at infinity the metric field approaches the usual Schwarzschild (Reissner-Nordström) limit, we demonstrate the absence of black hole type configurations.

Einstein‐Proca model: spherically symmetric solutions

AbstractThe Proca wave equation describes a classical massive spin 1 particle. We analyze the gravitational interaction of this vector field. In particular, the spherically symmetric solutions of the Einstein‐Proca coupled system are obtained numerically. Although at infinity the metric field approaches the usual Schwarzschild (Reissner‐Nordström) limit, we demonstrate the absence of black hole type configurations.

Intersecting D-branes and black holes in type 0 string theory

We study intersecting D-branes in type 0 string theories and show that the D$p_{\pm}$-brane bound states obey similar intersecting rules as the D$p$-branes of the type II theories. The D$5_{\pm}$-D$1_{\pm}$ brane system is studied in detail. We show that the corresponding near-horizon geometry is the $AdS_3\times S^3\times T^4$ space and that there is no tachyon instability in this background. The Bekenstein-Hawking entropy is calculated. The worldvolume theory on the D$5_{\pm}$-D$1_{\pm}$ system is also studied. This theory contains both bosons and fermions and it is seen to arise as a projection of the supersymmetric gauge theory related to the D5-D1 system of the type IIB theory. The Bekenstein-Hawking entropy formula is reproduced exactly using the dual conformal field theory.

(2+1)-dimensional stars

We investigate, in the framework of (2+1)-dimensional gravity, stationary rotationally symmetric gravitational sources of the perfect fluid type, embedded in a space of an arbitrary cosmological constant. We show that the matching conditions between the interior and exterior geometries imply restrictions on the physical parameters of the solutions. In particular, imposing finite sources and the absence of closed timelike curves privileges negative values of the cosmological constant, yielding exterior vacuum geometries of rotating black hole type. In the special case of static sources, we prove the complete integrability of the field equations and show that the sources' masses are bounded from above and, for a vanishing cosmological constant, generally equal to 1. We also discuss and illustrate the stationary configurations by explicitly solving the field equations for constant mass-energy densities. If the pressure vanishes, we recover as interior geometries G\"odel-like metrics defined on causally well behaved domains, but with unphysical values of the mass to angular momentum ratio. The introduction of pressure in the sources cures the latter problem and leads to physically more relevant models.

Comment on the Exterior Solutions and Their Geometry in Scalar-Tensor Theories of Gravity

We study series of the stationary solutions with asymptotic flatness properties in the Einstein-Maxwell-free scalar system because they are locally equivalent with the exterior solutions in some class of the scalar-tensor theories of gravity. First, we classify spherical exterior solutions into two types of the solutions, an apparently black hole type solution and an apparently worm hole type solution. The solutions contain three parameters, and we clarify their physical significance. Second, we reduce the field equations for the axisymmetric exterior solutions. We find that the reduced equations are partially the same as the Ernst equations. As simple examples, we derive new series of the static, axisymmetric exterior solutions, which correspond to Voorhees's solutions. We then show a non-trivial relation between the spherical exterior solutions and our new solutions. Finally, since null geodesics have conformally invariant properties, we study the local geometry of the exterior solutions by using the optical scalar equations and find some anomalous behaviors of the null geodesics.

Statistical entropy of charged two-dimensional black holes

The statistical entropy of a five-dimensional black hole in Type II string theory was recently derived by showing that it is U-dual to the three-dimensional Banados-Teitelboim-Zanelli black hole, and using Carlip's method to count the microstates of the latter. This is valid even for the non-extremal case, unlike the derivation which relies on D-brane techniques. In this letter, I shall exploit the U-duality that exists between the five-dimensional black hole and the two-dimensional charged black hole of McGuigan, Nappi and Yost, to microscopically compute the entropy of the latter. It is shown that this result agrees with previous calculations using thermodynamic arguments.

Structure and stability of cold scalar-tensor black holes

We study the structure and stability of the recently discussed spherically symmetric Brans-Dicke black-hole type solutions with an infinite horizon area and zero Hawking temperature, existing for negative values of the coupling constant $\omega$. These solutions split into two classes: B1, whose horizon is reached by an infalling particle in a finite proper time, and B2, for which this proper time is infinite. Class B1 metrics are shown to be extendable beyond the horizon only for discrete values of mass and scalar charge, depending on two integers $m$ and $n$. In the case of even $m-n$ the space-time is globally regular; for odd $m$ the metric changes its signature at the horizon. All spherically symmetric solutions of the Brans-Dicke theory with $\omega<-3/2$ are shown to be linearly stable against spherically symmetric \pns. This result extends to the generic case of the Bergmann-Wagoner class of scalar-tensor theories of gravity with the coupling function $\omega(\phi) < -3/2$.

Monopole and electrically charged dust thin shells in general relativity: Classical and quantum comparison of hollow and atomlike configurations

We give a comparative description of monopole and electrically charged spherically symmetric dust thin shells. Herewith we consider two of the most interesting configurations: the hollow shell and shell, surrounding a body with opposite charge. The classification of shells in accordance with the types of black holes and traversable wormholes is constructed. The theorems for the parameters of turning points are proved. Also for atomlike configurations the effects of screening (electrical case) and amplification (monopole case) of the internal mass by shell charge are studied. Finally, one considers the quantum aspects; herewith, exact solutions of wave equations and bound states spectra are found.

Size of black holes through polymer scaling

We imagine the strings on the stretched horizon of any $d$ space-time dimensional black hole to be bits of polymer. Then, proposing an interaction between these bits we obtain the size of the configuration, and thus of the black hole, using the scaling laws. The transition from a typical black hole state to a typical string state has a simple explanation, which also holds for the extremal black holes.

Emission from Isolated Black Holes and MACHO[CLC]s[/CLC] Accreting from the Interstellar Medium

Adopting the advection-dominated accretion flow (ADAF) model, we have reexamined the radiation emitted by isolated stellar-mass black holes accreting from the interstellar medium of our Galaxy. Two distinct types of black holes are given consideration: (1) remnants of conventional massive star evolution (remnant black holes [RBHs], mass ~10 M☉) and (2) low-mass objects that possibly constitute the dark halo and cause the observed microlensing events (MACHOBHs, mass ~0.5 M☉). In contrast to previous studies incorporating spherical accretion models, the characteristic hard X-ray emission from ADAFs serves as an important observational signature. Standard estimates for the present density of RBHs suggest that a fair number of objects, either in nearby molecular clouds (such as Orion) or in the general Galactic disk, may be detected by near-future X-ray instruments. Their observation may also be feasible at lower frequencies, particularly in the infrared and optical bands. On the other hand, the smaller mass and larger velocity on average of MACHOBHs compared with RBHs make them unlikely to be observable in the foreseeable future.

Do collapsed boson stars result in new types of black holes?

We prove a general no-hair theorem which is then applied to the case of a theory that consists of a number of complex scalar fields minimally coupled to gravity that vary harmonically with time and has an arbitrary potential. This establishes that in the spherically symmetric case there are no black hole analogues of the regular boson star configurations.

Quantum Black Hole. I

Using the Hartle-Hawking no-boundary proposal for the wave function of the universe, we can study the wave function and probability of a single black hole created at the birth of the universe. We begin with a quantum spherically symmetric model. At the semi-classical level, this turns out to be a 8 2 x 8 1 model. The black hole originates from a gravitational instanton with conical singularities. The wave function and probability of a universe with a black hole are calculated at the W K B level. The probability of black hole creation is the exponential of one quarter of the sum of the areas of the black hole and cosmological horizons. One quarter of this sum is the total entropy of the universe. The probability is an exponentially decreasing function of its mass parameter. It is conjectured that these arguments apply to all types of black holes in the de Sitter space background.

D-branes, moduli, and supersymmetry

We study toroidal compactifications of type II string theory with $D$-branes and nontrivial antisymmetric tensor moduli and show that turning on these fields modifies the supersymmetry projections imposed by $D$-branes. These modifications are seen to be necessary for the consistency of $T$ duality. We also show the existence of unusual BPS configurations of branes at angles that are supersymmetric because of conspiracies between moduli fields. Analysis of the problem from the point of view of the effective field theory of massless modes shows that the presence of a two-form background must modify the realization of supersymmetry on the brane. In particular, the appropriate supersymmetry variation of the physical gaugino vanishes in any constant field strength background. These considerations are relevant for the ${E}_{7(7)}$-symmetric counting of states of four-dimensional black holes in type II string theory compactified on ${T}^{6}$.