Kerr-Newman Black Hole Spacetimes Research Articles

Energy extraction, or lack thereof

The problem of stability of rotating black holes is the subject of a long standing research program since the 1960s and remains an unresolved problem in general relativity. A major obstacle in the black hole stability problem is that the energy of waves propagating through rotating black holes spacetimes is not necessarily positive-definite, due to the so called ergo-region. This is a serious complication that limits the efficacy of most mathematical techniques. In this expository article, we report that, despite the ergo-region, there exists a positive-definite total energy for axisymmetric Maxwell, gravitational and electrovacuum perturbations of Kerr and Kerr–Newman black hole spacetimes.

On the Radial Solutions of the Dirac Equation in the Kerr-Newman Black Hole Surrounded by a Cloud of Strings

In this paper, we obtain the metric of the space-time generated by a charged and rotating gravitational body surrounded by a loud of strings, namely, the Kerr–Newman black hole space-time with the addition of a cloud of strings. In this background, we find the radial solutions of the Dirac equation for massive particles and show that they are given in terms of the Generalized Heun functions. The dependence of these solutions on the parameter that codifies the presence of the cloud of strings is pointed out.

Curvature induced scalarization of Kerr-Newman black hole spacetimes

With certain nonminimal coupling between a massless scalar field and the Gauss-Bonnet curvature invariant in the extended scalar-tensor-Gauss-Bonnet (ESTGB) field theory, tachyonic instability of the Kerr-Newman (KN) black hole is promoted. Critical spin and charge for the onset of the spontaneous scalarization phenomenon for the KN black hole are calculated in the infinitely large coupling limit. Then the analytical formula for the coupling-strength-dependent critical existence line is obtained for the black-hole-scalar-field configuration in a finite large coupling regime. Moreover, numerical methods are used to perform threshold curves that are boundaries between bald KN black holes and their hairy counterparts. Intriguingly, we get to know the KN black hole can be scalarized in the vanishing spin limit in ESTGB theory.

Instability of the charged massive scalar field on the Kerr–Newman black hole spacetime

We investigate the quasibound states of charged massive scalar fields in the Kerr–Newman black hole spacetime by using a new approach recently developed, which uses the polynomial conditions of the Heun functions. We calculate the resonant frequencies related to the spectrum of quasibound states, as well as its corresponding angular and radial wave eigenfunctions. We also analyze the instability of the system. These results are particularized to the cases of Schwarzschild and Kerr black holes. Additionally, we compare our analytical results with the numerical ones known in the literature. Finally, we apply the obtained results to compute the characteristic times of growth and decay of bosonic particles around a supermassive black hole situated at the center of the M87 galaxy.

First Law of Black Hole Thermodynamics for the Kerr–Newman Spacetime Using Foliation

This article follows a simpler approach (Siddiqui et al. 2011) using the foliation concept with virtual displacement of hypersurfaces near the event horizon to derive the first law of black hole thermodynamics for the Kerr–Newman black hole spacetime.

The massive Dirac equation in the Kerr-Newman-de Sitter and Kerr-Newman black hole spacetimes

Exact solutions of the Dirac general relativistic equation that describe the dynamics of a massive, electrically charged particle with half-integer spin in the curved spacetime geometry of an electrically charged, rotating Kerr-Newman-(anti) de Sitter black hole are investigated. We first, derive the Dirac equation in the Kerr-Newman-de Sitter (KNdS) black hole background using a generalised Kinnersley null tetrad in the Newman-Penrose formalism. Subsequently in this frame and in the KNdS black hole spacetime, we prove the separation of the Dirac equation into ordinary differential equations for the radial and angular parts. Under specific transformations of the independent and dependent variables we prove that the transformed radial equation for a massive charged spin fermion in the background KNdS black hole constitutes a highly non-trivial generalisation of Heun’s equation since it possess five regular finite singular points. Using a Regge-Wheeler-like independent variable we transform the radial equation in the KNdS background into a Schrödinger like differential equation and investigate its asymptotic behaviour near the event and cosmological horizons. For the case of a massive fermion in the background of a Kerr-Newman (KN) black hole we first prove that the radial and angular equations that result from the separation of Dirac’s equation reduce to the generalised Heun differential equation (GHE). The local solutions of such GHE are derived and can be described by holomorphic functions whose power series coefficients are determined by a four-term recurrence relation. In addition using asymptotic analysis we derive the solutions for the massive fermion far away from the KN black hole and the solutions near the event horizon . The determination of the separation constant as an eigenvalue problem in the KN background is investigated. Using the aforementioned four-term recursion formula we prove that in the non-extreme KN geometry there are no bound states with , where ω and μ are the energy and mass of the fermion respectively.

The fingerprints of black holes—shadows and their degeneracies

We show that, away from the axis of symmetry, no continuous degeneration exists between the shadows of observers at any point in the exterior region of any Kerr–Newman black hole spacetime of unit mass. Therefore, except possibly for discrete changes, an observer can, by measuring the black holes shadow, determine the angular momentum and the charge of the black hole under observation as well as the observer’s radial position and angle of elevation above the equatorial plane. Furthermore, his/her relative velocity compared to a standard observer can also be measured. However, the black hole shadow does not allow for a full parameter resolution in the case of a Kerr–Newman–Taub–NUT black hole, as a continuous degeneration relating specific angular momentum, electric charge, Taub–NUT charge and elevation angle exists in this case.

Kerr-Newman black holes with stationary charged scalar clouds

It is shown that Kerr-Newman black holes can support linear charged scalar fields in their exterior regions. To that end, we solve analytically the Klein-Gordon wave equation for a stationary charged massive scalar field in the background of a near-extremal Kerr-Newman black hole. In particular, we derive a simple analytical formula which describes the physical properties of these stationary bound-state resonances of the charged massive scalar fields in the Kerr-Newman black-hole spacetime.

Black hole interior mass formula

AbstractWe argue by explicit computations that, although the area product, horizon radii product, entropy product, and irreducible mass product of the event horizon and Cauchy horizon are universal, the surface gravity product, the surface temperature product and the Komar energy product of the said horizons do not seem to be universal for Kerr–Newman black hole spacetimes. We show the black hole mass formula on the Cauchy horizon following the seminal work by Smarr [Phys Rev Lett 30:71 (1973), Phys Rev D 7:289 (1973)] for the outer horizon. We also prescribe the four laws of black hole mechanics for the inner horizon. A new definition of the extremal limit of a black hole is discussed.

Hawking radiation of Kerr-Newman black hole in different tortoise coordinate transformations

Hawking radiation effect of Maxwell’s electromagnetic fields in the Kerr-Newman black hole space-time is investigated using two different tortoise coordinate transformations. It has been shown that the new tortoise coordinate transformation produces constant term ξ in the expression of surface gravity and Hawking temperature. If ξ is set to zero, the surface gravity and Hawking temperature will be equal to those obtained from the old tortoise coordinate transformation. This indicates that new transformation is more reliable and accurate. The black body radiant spectrum of photon displays a new spin-rotation coupling effect.

Cosmic string in the NUT-Kerr-Newman spacetime

We study the equilibrium configurations of a cosmic string described by the Nambu action in the NUT-Kerr-Newman spacetime which includes as special cases the Kerr-Newman black hole spacetime as well as the NUT spacetime which is considered as a cosmological model. In this study it is interesting to note that one can obtain parallel results for the Kerr-Newman black hole as well as the NUT spacetime.

Quantum-mechanical instability of the Kerr-Newman black-hole interior

The behavior of the conserved stress-energy tensor of a quantized massless field in a Kerr-Newman black-hole space-time is studied. In the Unruh vacuum state, and under the assumption that certain stress-energy tensor components are analytic functions of a, the Kerr angular momentum parameter, it is shown that the stress-energy tensor must diverge on at least one of the two inner event horizons. A weaker assumption, simple continuity, suffices to guarantee that the stress-energy tensor diverges on the inner horizon of all slowly rotating Kerr-Newman black holes. This perturbation singularity invalidates the Kerr-Newman interior as a counterexample to strong cosmic censorship, and closes off the ''space bridge'' to other asymptotically flat exterior ''universes.''