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A charged black hole is a black hole that possesses electric charge. Since the electromagnetic repulsion in compressing an electrically charged mass is dramatically greater than the gravitational attraction (by about 40 orders of magnitude), it is not expected that black holes with a significant electric charge will be formed in nature.
The two types of charged black holes are Reissner–Nordström black holes (without spin), [1] and Kerr–Newman black holes (with spin).
A black hole can be completely characterized by three (and only three) quantities: [1]
Charged black holes are two of four possible types of black holes that have been found by solving Einstein's theory of gravitation, general relativity. The mathematical solutions for the shape of space and the electric and magnetic fields near a black hole are named after the persons who first worked them out. The solutions increase in complexity depending on which of the two parameters, J and Q, are zero (or not) (the mass M of a black hole could conceivably be tiny, but not zero). The four categories of solutions are given in the table below:
| Black hole type | Description | Constraints | |
|---|---|---|---|
| Schwarzschild | has no angular momentum and no electric charge | J = 0 | Q = 0 |
| Kerr | does have angular momentum but no electric charge | Q = 0 | |
| Reissner–Nordström | has no angular momentum but does have an electric charge | J = 0 | |
| Kerr–Newman | has both angular momentum and an electric charge | ||
The solutions of Einstein's field equation for the gravitational field of an electrically charged point mass (with zero angular momentum), in empty space was obtained in 1918 by Hans Reissner and Gunnar Nordström, not long after Karl Schwarzschild found the Schwarzschild metric as a solution for a point mass without electric charge and angular momentum.[ citation needed ]
A mathematically oriented article describes that the Reissner–Nordström metric for a charged, non-rotating black hole. [1] A similarly technical article on the Kerr–Newman black hole gives an overview of the most general known solution for a black hole, which has both angular momentum and charge (all the other solutions are simplified special cases of the Kerr–Newman black hole).
A gravitational singularity, spacetime singularity or simply singularity is a theoretical condition in which gravity is predicted to be so intense that spacetime itself would break down catastrophically. As such, a singularity is by definition no longer part of the regular spacetime and cannot be determined by "where" or "when". Gravitational singularities exist at a junction between general relativity and quantum mechanics; therefore, the properties of the singularity cannot be described without an established theory of quantum gravity. Trying to find a complete and precise definition of singularities in the theory of general relativity, the current best theory of gravity, remains a difficult problem. A singularity in general relativity can be defined by the scalar invariant curvature becoming infinite or, better, by a geodesic being incomplete.
Timeline of black hole physics
The no-hair theorem states that all stationary black hole solutions of the Einstein–Maxwell equations of gravitation and electromagnetism in general relativity can be completely characterized by only three independent externally observable classical parameters: mass, angular momentum, and electric charge. Other characteristics are uniquely determined by these three parameters, and all other information about the matter that formed a black hole or is falling into it "disappears" behind the black-hole event horizon and is therefore permanently inaccessible to external observers after the black hole "settles down". Physicist John Archibald Wheeler expressed this idea with the phrase "black holes have no hair", which was the origin of the name.
In general relativity, a white hole is a hypothetical region of spacetime and singularity that cannot be entered from the outside, although energy-matter, light and information can escape from it. In this sense, it is the reverse of a black hole, from which energy-matter, light and information cannot escape. White holes appear in the theory of eternal black holes. In addition to a black hole region in the future, such a solution of the Einstein field equations has a white hole region in its past. This region does not exist for black holes that have formed through gravitational collapse, however, nor are there any observed physical processes through which a white hole could be formed.
In Einstein's theory of general relativity, the Schwarzschild metric is an exact solution to the Einstein field equations that describes the gravitational field outside a spherical mass, on the assumption that the electric charge of the mass, angular momentum of the mass, and universal cosmological constant are all zero. The solution is a useful approximation for describing slowly rotating astronomical objects such as many stars and planets, including Earth and the Sun. It was found by Karl Schwarzschild in 1916.
The Penrose–Hawking singularity theorems are a set of results in general relativity that attempt to answer the question of when gravitation produces singularities. The Penrose singularity theorem is a theorem in semi-Riemannian geometry and its general relativistic interpretation predicts a gravitational singularity in black hole formation. The Hawking singularity theorem is based on the Penrose theorem and it is interpreted as a gravitational singularity in the Big Bang situation. Penrose shared half of the Nobel Prize in Physics in 2020 "for the discovery that black hole formation is a robust prediction of the general theory of relativity".
In the classical bosonic sector of a supersymmetric field theory, the Bogomol'nyi–Prasad–Sommerfield (BPS) bound provides a lower limit on the energy of static field configurations, depending on their topological charges or boundary conditions at spatial infinity. This bound manifests as a series of inequalities for solutions of the classical bosonic field equations. Saturating this bound, meaning the energy of the configuration equals the bound, leads to a simplified set of first-order partial differential equations known as the Bogomolny equations. Classical solutions that saturate the BPS bound are called "BPS states." These BPS states are not only important solutions within the classical bosonic theory but also play a crucial role in the full quantum supersymmetric theory, often corresponding to stable, non-perturbative states in both field theory and string theory. Their existence and properties are deeply connected to the underlying supersymmetry of the theory, even though the bound itself can be formulated within the bosonic sector alone.
The Kerr metric or Kerr geometry describes the geometry of empty spacetime around a rotating uncharged axially symmetric black hole with a quasispherical event horizon. The Kerr metric is an exact solution of the Einstein field equations of general relativity; these equations are highly non-linear, which makes exact solutions very difficult to find.
A rotating black hole is a black hole that possesses angular momentum. In particular, it rotates about one of its axes of symmetry.
In physics and astronomy, the Reissner–Nordström metric is a static solution to the Einstein–Maxwell field equations, which corresponds to the gravitational field of a charged, non-rotating, spherically symmetric body of mass M. The analogous solution for a charged, rotating body is given by the Kerr–Newman metric.
The Kerr–Newman metric describes the spacetime geometry around a mass which is electrically charged and rotating. It is a vacuum solution which generalizes the Kerr metric by additionally taking into account the energy of an electromagnetic field, making it the most general asymptotically flat and stationary solution of the Einstein–Maxwell equations in general relativity. As an electrovacuum solution, it only includes those charges associated with the magnetic field; it does not include any free electric charges.
In physics, there is a speculative hypothesis that, if there were a black hole with the same mass, charge and angular momentum as an electron, it would share other properties of the electron. Most notably, Brandon Carter showed in 1968 that the magnetic moment of such an object would match that of an electron. This is interesting because calculations ignoring special relativity and treating the electron as a small rotating sphere of charge give a magnetic moment roughly half the experimental value.
A ring singularity or ringularity is the gravitational singularity of a rotating black hole, or a Kerr black hole, that is shaped like a ring.
The mathematics of general relativity is complicated. In Newton's theories of motion, an object's length and the rate at which time passes remain constant while the object accelerates, meaning that many problems in Newtonian mechanics may be solved by algebra alone. In relativity, however, an object's length and the rate at which time passes both change appreciably as the object's speed approaches the speed of light, meaning that more variables and more complicated mathematics are required to calculate the object's motion. As a result, relativity requires the use of concepts such as vectors, tensors, pseudotensors and curvilinear coordinates.
The following outline is provided as an overview of and topical guide to black holes:
The Taub–NUT metric is an exact solution to Einstein's equations. It may be considered a first attempt in finding the metric of a spinning black hole. It is sometimes also used in homogeneous but anisotropic cosmological models formulated in the framework of general relativity.
In general relativity, the Weyl metrics are a class of static and axisymmetric solutions to Einstein's field equation. Three members in the renowned Kerr–Newman family solutions, namely the Schwarzschild, nonextremal Reissner–Nordström and extremal Reissner–Nordström metrics, can be identified as Weyl-type metrics.
Kerr–Schild perturbations are a special type of perturbation to a spacetime metric which only appear linearly in the Einstein field equations which describe general relativity. They were found by Roy Kerr and Alfred Schild in 1965.
