Simple Black Hole Research Articles

Metamaterial analog of a black hole shadow: An exact ray-tracing simulation based on the spacetime index of refraction

We show that the equation of null geodesics in spherically symmetric spacetimes in isotropic coordinates is identical to the equation of light ray trajectories in isotropic media in flat spacetime. Based on this analogy we introduce an exact simulation of the light ray trajectories both in these spacetimes and in their metamaterial analogs in terms of the spacetime index of refraction. As unstable light trajectories, the photon spheres form in these metamaterial analogs at exactly the same radial distances as expected from the corresponding black hole geometries. Using the same ray-tracing simulation we find the analog of a simple black hole shadow formed by the metamaterial analog of a Schwarzschild black hole, eclipsing a line of light sources near its analog horizon. Designing such a metamaterial could provide a laboratory setting to explore this recently observed phenomenon.

Black holes in the scalar-tensor formulation of 4D Einstein-Gauss-Bonnet gravity: Uniqueness of solutions, and a new candidate for dark matter

In this work we study static black holes in the regularized 4D Einstein-Gauss-Bonnet theory of gravity; a shift-symmetric scalar-tensor theory that belongs to the Horndeski class. This theory features a simple black hole solution that can be written in closed form, and which we show is the unique static, spherically-symmetric and asymptotically-flat black hole vacuum solution of the theory. We further show that no asymptotically-flat, time-dependent, spherically-symmetric perturbations to this geometry are allowed, which suggests that it may be the only spherically-symmetric vacuum solution that this theory admits (a result analogous to Birkhoff's theorem). Finally, we consider the thermodynamic properties of these black holes, and find that their final state after evaporation is a remnant with a size determined by the coupling constant of the theory. We speculate that remnants of this kind from primordial black holes could act as dark matter, and we constrain the parameter space for their formation mass, as well as the coupling constant of the theory.

Lost horizon? – modeling black holes in string theory

The modeling of black holes is an important desideratum for any quantum theory of gravity. Not only is a classical black hole metric sought, but also agreement with the laws of black hole thermodynamics. In this paper, we describe how these goals are obtained in string theory. We review black hole thermodynamics, and then explicate the general stringy derivation of classical spacetimes, the construction of a simple black hole solution, and the derivation of its entropy. With that in hand, we address some important philosophical and conceptual questions: the confirmatory value of the derivation, the bearing of the model on recent discussions of the so-called 'information paradox', and the implications of the model for the nature of space.

Charged black-bounce spacetimes

Given the recent development of rotating black-bounce-Kerr spacetimes,for both theoretical and observational purposes it becomes interesting to see whether it might be possible to construct black-bounce variants of the entire Kerr-Newman family.Specifically, herein we shall consider black-bounce-Reissner-Nordström and black-bounce-Kerr-Newman spacetimes as particularly simple and clean everywhere-regular black hole “mimickers” that deviate from the Kerr-Newman family in a precisely controlled and minimal manner, and smoothly interpolate between regular black holes and traversable wormholes.While observationally the electric charges on astrophysical black holes are likely to be extremely low, |Q|/m ≪ 1, introducing any non-zero electric charge has a significant theoretical impact. In particular, we verify the existence of a Killing tensor (and associated Carter-like constant) but without the full Killing tower of principal tensor and Killing-Yano tensor, also we discuss how, assuming general relativity, the black-bounce-Kerr-Newman solution requires an interesting, non-trivial matter/energy content.

Thermodynamics of asymptotically flat Reissner–Nordstrom black hole

We established the criteria for thermal stability of a most general black hole in the form of a series of inequalities connecting second-order derivatives of the black hole mass with respect to its parameters. The mass of a black hole depends solely on these parameters, e.g. horizon area and electric charge are these parameters for non-rotating charged black hole. We also introduced the notion of “Quasi stability”. It is known how to calculate the fluctuations of these parameters for both stable and quasi stable black holes. In this paper, we consider the simplest black hole having nontrivial parameter, i.e. electrically charged non-rotating asymptotically flat Reissner–Nordstrom black hole (AFRNBH). We will show here that this black hole is not stable anywhere in its parameter space, but it is actually quasi stable, having positive specific heat in some region, violating Hawking’s prediction. In fact, this black hole will be shown to exhibit phase transition which is structurally quite different from that in case of Schwarzschild black hole, as predicted first by Hawking. This black hole will also be shown to try to resist its decay under Hawking radiation, but ultimately remains unsuccessful.

Nonlogarithmic divergence of a deflection angle by a marginally unstable photon sphere of the Damour-Solodukhin wormhole in a strong deflection limit

Static, spherically symmetric black holes and compact objects without an event horizon have unstable (stable) circular orbits of a light called photon (antiphoton) sphere. A Damour-Solodukhin wormhole has been suggested as a simple black hole mimicker and the difference of its metric tensors from a black hole is described by a dimensionless parameter $\lambda$. The wormhole with two flat regions has two photon spheres and an antiphoton sphere for $\lambda<\sqrt{2}/2$ and a photon sphere for $\lambda \geq \sqrt{2}/2$. When the parameter $\lambda$ is $\sqrt{2}/2$, the photon sphere is marginally unstable because of degeneration of the photon spheres and antiphoton sphere. We investigate gravitational lensing by the wormhole in weak and strong gravitational fields. We find that the deflection angle of a light ray reflected by the marginally unstable photon sphere diverges nonlogarithmically in a strong deflection limit for $\lambda=\sqrt{2}/2$, while the deflection angle reflected by the photon sphere diverges logarithmically for $\lambda \neq \sqrt{2}/2$. We extend a strong deflection limit analysis for the nonlogarithmic divergence case. We expect that our method can be applied for gravitational lenses by marginally unstable photon spheres of various compact objects.

Lightweight reputation-based approach against simple and cooperative black-hole attacks for MANET

Ad hoc network is a set of mobile nodes interconnected by wireless communication. It is easily and less expensive to deploy, but it is vulnerable against various attacks. The node data should cross a set of intermediate nodes in order to reach the intended destination. An intermediate node, which takes part of the routing process, can behave maliciously and drop the packets passing through it instead of transferring them to its successor, which leads to what is called black hole attack. Several solutions have been proposed in the literature review. However, these solutions suffer from the imbalance between robustness and overhead. In this context, we propose a solution based on reputation of nodes and multi-hop acknowledgment. The reputation of nodes increases or decreases depending on the situation and the observation condition. When the node reputation passes below the threshold, then it will be considered as a black hole node. The proposed approach detects and excludes simple and cooperative black hole attackers and enforces the cooperation among the network nodes. Through simulation, we compare the proposed approach to a concurrent protocol and we show its efficiency in terms of detection ratio and communication overhead.

Simple regular black hole with logarithmic entropy correction

A simple regular black hole solution satisfying the weak energy condition is obtained within Einstein--non--linear electrodynamics theory. We have computed the thermodynamic properties of this black hole by a careful analysis of the horizons and we have found that the usual Bekenstein--Hawking entropy gets corrected by a logarithmic term. Therefore, in this sense our model realizes some quantum gravity predictions which add this kind of correction to the black hole entropy. In particular, we have established some similitudes between our model and a quadratic generalized uncertainty principle. This similitude has been confirmed by the existence of a remnant, which prevents complete evaporation, in agreement with the quadratic generalized uncertainty principle case.

Cosmic censorship in Lorentz-violating theories of gravity

Is Cosmic Censorship special to General Relativity, or can it survive a violation of equivalence principle? Recent studies have shown that singularities in Lorentz violating Einstein-Aether (or Horava-Lifhsitz) theories can lie behind a universal horizon in simple black hole spacetimes. Even infinitely fast signals cannot escape these universal horizons. We extend this result, for an incompressible aether, to 3+1d dynamical or spinning spacetimes which possess inner killing horizons, and show that a universal horizon always forms in between the outer and (would-be) inner horizons. This finding suggests a notion of Cosmic Censorship, given that geometry in these theories never evolves beyond the universal horizon (avoiding potentially singular inner killing horizons). A surprising result is that there are 3 distinct possible stationary universal horizons for a spinning black hole, only one of which matches the dynamical spherical solution. This motivates dynamical studies of collapse in Einstein-Aether theories beyond spherical symmetry, which may reveal instabilities around the spherical solution.

Paczynski-Wiita-like potential for any static spherical black hole in metric theories of gravity

The pseudo-Newtonian potential of Paczynski and Wiita for particles orbiting a Schwarzschild black hole is generalized to arbitrary static and spherically symmetric spacetimes, including black hole solutions of alternative theories of gravity. In addition to being more general, our prescription differs substantially from a previous one in the literature, showing that even the association of a pseudo-Newtonian potential with a simple black hole metric is not unique.

Struggling against simple and cooperative black hole attacks in multi-hop wireless ad hoc networks

In multi-hop wireless ad hoc networks, nodes not in direct range rely on intermediate nodes to communicate. In order to preserve its limited resources or to launch a DoS attack, an intermediate node drops packets going through it instead to forward them to its successor. In this paper, we deal with this misbehavior called black hole attack, and we propose an authenticated end-to-end acknowledgment based approach in order to check the correct forwarding of packets by intermediate nodes. Our approach detects the black hole conducted in simple or cooperative manner, the modification and the replay of messages attacks. Through simulation using OPNET simulator, we show the detection efficiency and evaluate the performance of our approach in both proactive and reactive routing based networks in terms of end-to-end delay and network load. Also, we compare the approach we propose with 2-hop ACK and the watchdog approaches in terms of detection ratio, delivery ratio and additional overhead.

Nonexistence of black holes with noncanonical scalar fields

We study the existence of stationary black holes with a non-canonical scalar field as a matter source. We prove a simple black hole no-hair theorem which rules out the existence of asymptotically flat black holes which are static or stationary and axisymmetric possessing scalar hair for a wide class of non-canonical scalar field theories. This applies to scalar field theories which are of the form of K-essence theories. In particular, we rule out the existence of such black holes in the ghost condensate model, and in large sectors of the Dirac-Born-Infeld model.

Holographic stress tensor for non-relativistic theories

We discuss the calculation of the field theory stress tensor from the dual geometry for two recent proposals for gravity duals of non-relativistic conformal field theories. The first of these has a Schrödinger symmetry including Galilean boosts, while the second has just an anisotropic scale invariance (the Lifshitz case). For the Lifshitz case, we construct an appropriate action principle. We propose a definition of the non-relativistic stress tensor complex for the field theory as an appropriate variation of the action in both cases. In the Schrödinger case, we show that this gives physically reasonable results for a simple black hole solution and agrees with an earlier proposal to determine the stress tensor from the familiar AdS prescription. In the Lifshitz case, we solve the linearised equations of motion for a general perturbation around the background, showing that our stress tensor is finite on-shell.

More onN=8attractors

We examine a few simple extremal black hole configurations of $\mathcal{N}=8$, $d=4$ supergravity. We first elucidate the relation between the BPS Reissner-N\ordstrom black hole and the non-BPS Kaluza-Klein dyonic black hole. Their classical entropy, given by the Bekenstein-Hawking formula, can be reproduced via the attractor mechanism by suitable choices of symplectic frame. Then, we display the embedding of the axion-dilaton black hole into $\mathcal{N}=8$ supergravity.

FALLING INTO A BLACK HOLE

String theory tells us that quantum gravity has a dual description as a field theory (without gravity). We use the field theory dual to ask what happens to an object as it falls into the simplest black hole: the two-charge extremal hole. In the field theory description the wave function of a particle is spread over a large number of "loops," and the particle has a well-defined position in space only if it has the same "position" on each loop. For the infalling particle we find one definition of "same position" on each loop, but there is a different definition for outgoing particles and no canonical definition in general in the horizon region. Thus the meaning of "position" becomes ill-defined inside the horizon.

Quantum information in loop quantum gravity

A coarse-graining of spin networks is expressed in terms of partial tracing, thus allowing to use tools of quantum information theory. This is illustrated by the analysis of a simple black hole model, where the logarithmic correction of the Bekenstein-Hawking entropy is shown to be equal to the total amount of correlations on the horizon. Finally other applications of entanglement to quantum gravity are briefly discussed.

Golden Binary Gravitational‐Wave Sources: Robust Probes of Strong‐Field Gravity

Space-borne gravitational-wave interferometers such as LISA will detect the gravitational wave (GW) signal from the inspiral, plunge, and ringdown phases of massive black hole binary mergers at cosmological distances. From the inspiral waves, we will be able to measure the masses of the binaries' members; from the ringdown waves, we will be able to measure the mass of the final merged remnant. A subset of detected events allow the identification of both the inspiral and the ringdown waveforms in a given source and thus allow a measurement of the total mass-energy lost to GWs over the coalescence, MGW. We define "golden" binary mergers to be those with measurement errors likely to be small enough for a physically useful determination of MGW. A detailed sensitivity study, combined with simple black hole population models, suggests that a few golden binary mergers may be detected during a 3 yr LISA mission lifetime. Any such mass deficit measurement would constitute a robust and valuable observational test of strong-field relativistic gravity. An extension of this concept to include spin measurements may allow a direct empirical test of the black hole area theorem.

A Simple Black Hole Model of Quasar Abundance and Evolution in the Infinitely Long Cosmic-String Scheme

view Abstract Citations (1) References (76) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Simple Black Hole Model of Quasar Abundance and Evolution in the Infinitely Long Cosmic-String Scheme Hara, Tetsuya ; Yamamoto, Hideki ; Maehoenen, Petri ; Miyoshi, Shigeru J. Abstract The formation and evolution of quasars are investigated in relation to the infinitely long cosmic-string scheme. Using the mass function of high-density sites of cold dark matter in the cosmic-string model, a simple black hole model for the evolution of quasar abundance and luminosity function is developed by assuming an appropriate gas accretion rate into the central black holes. To compare with the observations, we apply statistical methods, assuming a Gaussian distribution, to the formation epoch of quasar host galaxies z_G_, to the mass fraction F of host-galaxy-fueling central black holes, and to the radiative efficiency ɛ, respectively. There is a time lag between the formation of host galaxies and the birth of high-redshift quasars. The simulated results with reasonable parameter values are in good agreement with the observed evolution of quasar abundance and luminosity function. It is necessary to have enough nonlinear regions for host galaxies at around z ~ 7 to adequately reproduce the observations. Publication: The Astrophysical Journal Pub Date: May 1996 DOI: 10.1086/177176 Bibcode: 1996ApJ...462..601H Keywords: COSMIC STRINGS; COSMOLOGY: THEORY; GALAXIES: FUNDAMENTAL PARAMETERS; GALAXIES: QUASARS: GENERAL; BLACK HOLE PHYSICS full text sources ADS |

Colors of Objects in the Field of the Double Quasi-Stellar Object 1146+111B,C

Color images of faint objects were used to test two hypotheses for the quasi-stellar object (QSO) pair 1146+ 111B,C: gravitational lens or massive string. Blue, red, and near-infrared CCD (charge-coupled device) images of the field of this QSO pair were examined for gravitational lens multiple-image candidates for all four QSO's in the field (B, C, D, and E). No third image of 1146+111B,C was found, down to 4 magnitudes fainter than BC. This result implies a compact lens mass distribution, if B and C are images of the same QSO. C appears to be redder than B in the wavelength region from 700 to 1100 nanometers. This raises the question of whether B and C are images of the same QSO. Three blue stellar objects of unusual color were found at plausible locations for multiple images of the other two QSO's in the field. A very red object was found at a plausible lens position. Under the hypothesis that B and C are lensed images, these color data severely restrict the possible lens models and imaged QSO multiplicities. One possibility is a compact lens mass of 4 x 10(15) solar masses at a redshift of 0.8. Another is an S-shaped massive string. If the spectrum of any of the three anomalous blue objects were available, it would be possible to distinguish between these two models. However, it is difficult to fit the color and intensity data reported here to either simple string or black hole models. Overall, the simplest model consistent with all the data is the no-lens, no-string hypothesis: B and C probably are separate QSO's, but with some spectral similarities.

Possible evidence for a massive black hole in a quasar with double redshift systems

With the aid of a simple black hole model of quasars we have found that the majority of the distinguishable emission lines in the spectrum of the quasar 1604+179 can be assigned to two redshift systems,zr=3.712 andzb=2.701. The appearance of double emission redshifts means that this quasar might be a massive black hole (of mass 108M•≤M≤1011M•) with a ring-like emission line region (of radius 1 light-day ≤r0≤1 light-year) in its accretion disk.