Acceleration of particles by nonrotating charged black holes?

Recently, in the series of works a new effect of acceleration of particles by black holes has been found. Under certain conditions, the energy in the center-of-mass system can become infinitely large. The essential ingredient of such effect is the rotation of a black hole. In this work, it has been argued that the similar effect exists for a nonrotating but charged black hole even for the simplest case of radial motion of particles in the Reissner-Nordström background. All main features of the effect under discussion due to rotating black holes have their counterpart for the nonrotating charged ones.     

Center-of-mass energy for the Plebanski-Demianski black hole

We study the center-of-mass energy of the particles colliding in the vicinity of acceleration and event horizons of the Plebanski and Demianski class of black holes. We calculate the collision energy of uncharged particles in the center-of-mass frame that are freely falling along the equatorial plane of a charged accelerating and rotating black hole with an NUT parameter. This energy turns out to be infinite in the non-extremal case, while in the extremal case, it becomes infinitely large near the event horizon only if the particle has the critical angular momentum. We conclude that the center-of-mass energy depends on the rotation and the NUT parameter.     

Particle acceleration in Horava–Lifshitz black holes

In this paper we calculate the center-of-mass energy of two colliding test particles near the rotating and non-rotating Horava–Lifshitz black hole. For the case of a slowly rotating KS solution of Horava–Lifshitz black hole we compare our results with the case of Kerr black holes. We confirm the limited value of the center-of-mass energy for static black holes and unlimited value of the center-of-mass energy for rotating black holes. Numerically, we discuss temperature dependence of the center-of-mass energy on the black hole horizon. We obtain the critical angular momentum of particles. In this limit the center-of-mass energy of two colliding particles in the neighborhood of the rotating Horava–Lifshitz black hole could be arbitrarily high. We found appropriate conditions where the critical angular momentum could have an orbit outside the horizon. Finally, we obtain the center-of-mass energy corresponding to this circle orbit.     

Statistical entropies of extremal Kaluza-Klein AdS black holes in arbitrary dimensions

We have investigated the microscopic interpretations of the entropies for the four-dimensional extremal Kaluza-Klein AdS black hole and its higher-dimensional generalizations by using the Kerr/CFT correspondence. These newly-found Kaluza-Klein AdS black holes are charged rotating asymptotically AdS black hole solutions of gauged supergravity in four and higher dimensions. With suitable boundary conditions on the perturbations of the near-horizon geometry, it is shown that the asymptotic symmetry generators form a two-dimensional Virasoro algebra with a central term. By utilizing the central charge and the temperature of the dual conformal field theory, Cardy formula reproduces the expected Bekenstein-Hawking entropy. Directly working on the ordinary metrics of the extremal Kaluza-klein AdS black holes without taking the near-horizon limit, we also re-derive their microscopic entropies.     

Hawking Radiation via Damour-Ruffini Method in Squashed Charged Rotating Kaluza-Klein Black Holes

Using the Damour-Ruffini method, Hawking radiation of charged particles from squashed charged rotating five-dimensional Kaluza-Klein black holes is investigated extensively. Under the generalized tortoise coordinate transformation, Hawking temperature of the black holes is calculated by using charged scalar particles and Dirac fermions respectively. We find that the obtained Hawking temperature for charged Dirac fermions is the same as for charged scalar particles. What’s more, the spectrum of Hawking radiation contains the information of the size of the extra dimension, which could provide insight for further investigation of large extra dimensions in the future.     

Rotating Charged Hairy Black Hole in (2+1) Dimensions and Particle Acceleration

In this paper, we construct rotating charged hairy black hole in (2+1) dimensions for infinitesimal black hole charge and rotation parameters. Then we consider this black hole as particle accelerator and calculate the center-of-mass energy of two colliding test particles near the rotating charged hairy black hole in (2+1) dimensions. As we expected, the center-of-mass energy has infinite value.     

Destroying Extremal Kerr-Newman-AdS Black Holes with Test Particles

Neglecting the self-force,self-energy and radiative effects,we follow the spirit of Wald's gedanken experiment and further discuss whether an extremal Kerr-Newman-AdS(KNA)black hole can turn into a naked singularity when it captures charged and spinning massive particles.It is found that feeding a test particle into an extremal KNA black hole could lead to a violation of cosmic censorship for the black hole.     

Effects of acceleration on the collision of particles in the rotating black hole spacetime

We study the collision of two geodesic particles in the accelerating and rotating black hole spacetime and probe the effects of the acceleration of black hole on the center-of-mass energy of the colliding particles and on the high-velocity collision belts. We find that the dependence of the center-of-mass energy on the acceleration in the near event-horizon collision is different from that in the near acceleration-horizon case. Moreover, the presence of the acceleration changes the shape and position of the high-velocity collision belts. Our results show that the acceleration of black holes brings about richer physics for the collision of particles.     

Angular Momentum-Free of the Entropy Relations for Rotating Kaluza-Klein Black Holes

Based on a mathematical lemma related to the Vandermonde determinant and two theorems derived from the first law of black hole thermodynamics, we investigate the angular momentum independence of the entropy sum as well as the entropy product of general rotating Kaluza-Klein black holes in higher dimensions. We show that for both non-charged rotating Kaluza-Klein black holes and non-charged rotating Kaluza-Klein-AdS black holes, the angular momentum of the black holes will not be present in entropy sum relation in dimensions d≥4, while the independence of angular momentum of the entropy product holds provided that the black holes possess at least one zero rotation parameter a _j = 0 in higher dimensions d≥5, which means that the cosmological constant does not affect the angular momentum-free property of entropy sum and entropy product under the circumstances that charge δ=0. For the reason that the entropy relations of charged rotating Kaluza-Klein black holes as well as the non-charged rotating Kaluza-Klein black holes in asymptotically flat spacetime act the same way, it is found that the charge has no effect in the angular momentum-independence of entropy sum and product in asymptotically flat spactime.     

Rotating Charged Hairy Black Hole in(2+1) Dimensions and Particle Acceleration

In this paper, we construct rotating charged hairy black hole in(2+1) dimensions for infinitesimal black hole charge and rotation parameters. Then we consider this black hole as particle accelerator and calculate the centerof-mass energy of two colliding test particles near the rotating charged hairy black hole in(2+1) dimensions. As we expected, the center-of-mass energy has infinite value.     

Extremal static AdS black hole/CFT correspondence in gauged supergravities

A recently proposed holographic duality allows the Bekenstein–Hawking entropy of extremal rotating black holes to be calculated microscopically, by applying the Cardy formula to the two-dimensional chiral CFTs associated with certain reparameterisations of azimuthal angular coordinates in the solutions. The central charges are proportional to the angular momenta of the black hole, and so the method degenerates in the case of static (non-rotating) black holes. We show that the method can be extended to encompass such charged static extremal AdS black holes by using consistent Kaluza–Klein sphere reduction ansatze to lift them to exact solutions in the low-energy limits of string theory or M-theory, where the electric charges become reinterpreted as angular momenta associated with internal rotations in the reduction sphere. We illustrate the procedure for the examples of extremal charged static AdS black holes in four, five, six and seven dimensions.     

Magnetic charge,black holes,and cosmic censorship

The possibility of converting a Reissner-Nordström black hole into a naked singularity by means of test particle accretion is considered. The dually charged Reissner-Nordström metric describes a black hole only when M² > Q³ + P². The test particle equations of motion are shown to allow test particles with arbitrarily large magnetic charge/mass ratios to fall radially into electrically charged black holes. To determine the nature of the final state (black hole or naked singularity) an exact solution of Einstein's equations representing a spherical shell of magnetically charged dust falling into an electrically charged black hole is studied. Naked singularities are never formed so long as the weak energy condition is obeyed by the infalling matter. The differences between the spherical shell model and an infalling point test particle are examined and discussed.     

On the collisions between particles in the vicinity of rotating black holes

Scattering of particles in the gravitational field of rotating black holes is considered. It is shown that scattering energy of particles in the centre of mass system can obtain very large values not only for extremal black holes but also for nonextremal ones. Extraction of energy after the collision is investigated. It is shown that due to the Penrose process the energy of the particle escaping the hole at infinity can be large. Contradictions in the problem of getting high energetic particles escaping the black hole are resolved.     

Distinguishing between Kerr and rotating JNW space-times via frame dragging and tidal effects

We investigate two physical quantities that might observationally distinguish between Kerr black holes and rotating naked singularities. These are the Lense–Thirring precession frequency as measured by a Copernican observer, and tidal forces. We establish strong enhancement for both these quantities due to a Janis–Newman–Winicour naked singularity background, as compared to the Kerr case. We first show that the precession frequency of a test gyroscope at a given radius can be enhanced by almost an order of magnitude in the background of the naked singularity, as compared to the Kerr black hole. We then show that a critical mass for celestial objects below which these disintegrate due to tidal forces might increase by more than an order of magnitude in the naked singularity background, compared to the black hole. Our results complement the existing ones in the literature regarding differences in observable quantities in such backgrounds, and might be of significance in futuristic experiments.     

General nonextremal rotating black holes in minimal five-dimensional gauged supergravity

We construct the general solution for nonextremal charged rotating black holes in five-dimensional minimal gauged supergravity. They are characterized by four nontrivial parameters: namely, the mass, the charge, and the two independent rotation parameters. The metrics in general describe regular rotating black holes, providing the parameters lie in appropriate ranges so that naked singularities and closed timelike curves (CTCs) are avoided. We calculate the conserved energy, angular momenta, and charge for the solutions, and show how supersymmetric solutions arise in a Bogomol'nyi-Prasad-Sommerfield limit. These have naked CTCs in general, but for special choices of the parameters we obtain new regular supersymmetric black holes or smooth topological solitons.     

Particle collisions near the cosmological horizon of a Reissner-Nordström-de Sitter black hole

It has recently been shown that black holes can act as particle accelerators and two particles can collide with arbitrarily high center-of-mass (CM) energy under certain critical conditions. In this paper, we investigate particle collisions outside a Reissner-Nordström-de Sitter (RN-dS) black hole. We find that infinite CM energy can be produced near the cosmological horizon for generic spacetime configurations. Remarkably, such infinite CM energy does not require the black hole to be extremal, in contrast to spacetimes in the absence of cosmological constants. However, since the charge of an astrophysical body is negligible, the required charge to mass ratio of the particle is extremely higher than that of any elementary particle.     

Tunneling Radiation of Massive Vector Bosons from Dilaton Black Holes

It is well known that Hawking radiation can be treated as a quantum tunneling process of particles from the event horizon of black hole. In this paper, we attempt to apply the massive vector bosons tunneling method to study the Hawking radiation from the non-rotating and rotating dilaton black holes. Starting with the Proca field equation that govern the dynamics of massive vector bosons, we derive the tunneling probabilities and radiation spectrums of the emitted vector bosons from the static spherical symmetric dilatonic black hole, the rotating Kaluza-Klein black hole, and the rotating Kerr-Sen black hole. Comparing the results with the blackbody spectrum, we satisfactorily reproduce the Hawking temperatures of these dilaton black holes, which are consistent with the previous results in the literature.     

Polar orbits in the Kerr space-time

The motion of test particles in polar orbit about the source of the Kerr field of gravity is studied, using Carter's first integrals for timelike geodesies in the Kerr space-time. Expressions giving the angular coordinates of such particles as functions of the radial one are derived, both for the case of a rotating black hole as well as for that of a naked singularity.     

Black hole emissions and phase transitions

The nonthermal emission of a rotating black hole is related to the inner horizon of the hole. The transition from the Kerr black hole state to the naked singularity state is considered as a phase transition. An arrangement of the energetics of Kerr black holes into a two-phase thermodynamics is suggested.     

Extremal Einstein–Born–Infeld black holes in dilaton gravity

Motivated by considerable interests of Myers–Perry black holes, we employ the perturbative method to obtain a family of extremal charged rotating black hole solutions in odd dimensional Einstein–Born–Infeld-dilaton gravity. We start with an extremal Myers–Perry black hole with equal angular momenta, and then by adding the dilaton field and the nonlinear Born–Infeld electrodynamics, we find an extremal nonlinearly charged rotating black holes. The perturbative parameter is assumed to be the electric charge q$q$ and the perturbations are performed up to the third order. We then study the physical properties of these Born–Infeld-dilaton black holes. In particular, we show that the perturbative parameter, q$q$, the dilaton coupling constant, α$\alpha$, and the Born–Infeld parameter, β$\beta$, modify the Smarr formula and the values of the gyromagnetic ratio of the extremal charged rotating black holes.