Recently, a generalised solution for Einstein equations of a rotating compact body, surrounded by matter field was proposed, which is the Kerr-Newman spacetime with an anisotropic matter. The solution possesses an additional hair, along with the conventional mass, charge and spin, which arises from the negative radial pressure of the anisotropic matter. In this article we show that, this new class of black holes can act as a particle accelerator during the collision of two generic particles in its gravitational field in the ergo-region. The centre of mass energy of the particles shoots to arbitrary high value in the vicinity of event horizon for the extremal black hole. The physical conditions for the collision to take place are obtained by studying the horizon structure and circular particle motion. The results are interesting from astrophysical perspective.
It has recently been pointed out that arbitrary center-of-mass energies may be obtained for particle collisions near the horizon of an extremal Kerr black hole. We investigate this mechanism in cylindrical topology. In particular we consider the center-of-mass energies of a cylindrical black hole with an extremal rotation and charge parameter. The geodesics are first derived with a rotating charged cylindrical black hole producing the background gravitational field. Finally the center-of-mass is determined for this background and its extremal limit is taken.
Recently, Banãdos, Silk and West (BSW) demonstrated that the extremal Kerr black hole can act as a particle accelerator with arbitrarily high center-of-mass energy ($E_{CM}$) when the collision takes place near the horizon. The rotating Hayward's regular black hole, apart from Mass ($M$) and angular momentum ($a$), has a new parameter $g$ ($g>0$ is a constant) that provides a deviation from the Kerr black hole. We demonstrate that for each $g$, with $M=1$, there exist critical $a_{E}$ and $r_{H}^{E}$, which corresponds to a regular extremal black hole with degenerate horizon, and $a_{E}$ decre…
We demonstrate that the four-dimensional Gauss-Bonnet black hole can act as a particle accelerator with arbitrarily high centre-of-mass energy, during the collision of two general particles near the event horizon. The Gauss-Bonnet coupling constant $α$, provides a deviation in the results from that of Kerr black hole. Our results show that the horizon structure, the range of allowed angular momentum and the critical angular momentum depend on the value of $α$. For extremal cases, the centre-of-mass energy diverges near the horizon, suggesting that Gauss-Bonnet black hole can also act as a part…
Here we look at an application of the Hartle metric to describe a rotating version of the spherical string cloud/ global monopole solution. While rotating versions of this solution have previously been constructed via the Newman-Janis algorithm, that process does not preserve the equation of state. The Hartle method allows for preservation of equation of state, at least in the sense of a slowly rotating perturbative solution. In addition to the direct utility of generating equations which could be used to model a region of a rotating string cloud or similar system, this work shows that it is p…
The stability of static uncharged spheres with anisotropic internal stresses is studied in general relativity. It has been noticed that pressure anisotropy plays an important role for stability of stellar structure. It is shown that radial profile of the stress anisotropy can be considered to decide potentially stable/unstable regions. Finally, pontentially stable/unstable regions of two known models of relativistic star have been examined.
In this paper, we study the shadow produced by rotating black holes with charge in the presence of an anisotropic matter field. We obtain the apparent shape and the corresponding observables characterizing the size, oblateness, and deviation of the center, for different values of the parameters of the model. We compare the new results with those corresponding to the Kerr-Newmann spacetime and we also discuss the observational prospects in this case.
Rotating and non-linear magnetic-charged black hole with an anisotropic matter field
School of Physics Science and Technology, Xinjiang University（新疆大学物理科学与技术学院）；Faculty of Science, Kunming University of Science and Technology（昆明理工大学理学院）
An exact rotating anisotropic fluid solution and a family of exact rotating anisotropic fluid solutions are presented which satisfy all energy conditions for certain values of their parameters. The components of the Ricci tensor the eigenvalues of this tensor and the energy-momentum tensor of the solutions are given explicitly. All have the ring singularity of Kerr's solution and in addition the solution one more singularity and some solutions of the family additional singularities.The solution matches to the extremal solution of Kerr on two surfaces, which are thin shells and for proper value…
A double new class of solutions to the general relativity field equations describing interior spacetimes sourced by stationary cylindrical anisotropic fluids with principal stress directed along the symmetry axis is displayed. These solutions are required to satisfy regularity and junction conditions so that they can be possibly used to represent rotating astrophysical objects. Mathematical and physical properties are analyzed. The spacetime two independent parameters are physically interpreted, and they are shown to define two different solution classes together with stating the latters' prop…
We present a family of exact rotating anisotropic fluid solutions, which satisfy all energy conditions for certain values of their parameters. The components of the Ricci tensor $R_{μν}$ the eigenvalues of the tensor $R_μ^ν$ and the energy-momentum tensor $T_{μν}$ of the solutions are given explicitly. All members of the family have the ring singularity of Kerr's solution and most of them one or two more singularities. The solutions can be matched to the solution of Kerr on three closed surfaces, which for proper values of the parameters of the solutions approximate oblate spheroids. All match…
Within the framework of $f(R,T)$ theories of gravity, we investigate the hydrostatic equilibrium of anisotropic neutron stars with a physically relevant equation of state (EoS) for the radial pressure. In particular, we focus on the $f(R,T) = R+ 2βT$ model, where $β$ is a minimal coupling constant. In the slowly rotating approximation, we derive the modified TOV equations and the expression for the relativistic moment of inertia. The main properties of neutron stars, such as radius, mass and moment of inertia, are studied in detail. Our results revel that the main consequence of the $2βT$ term…
Given an anisotropic fluid source, we determine in closed forms, upon solving the field equations of general relativity (GR) and teleparallel gravity (TEGR) coupled to a cosmological constant, cylindrically symmetric four-dimensional cosmological rotating wormholes, satisfying all local energy conditions, and cosmological rotating solutions with two axes of symmetry at finite proper distance. These solutions have the property that their angular velocity is proportional to the cosmological constant.
We study the collision of two particles with equal masses moving in the equatorial plane near horizon of the rotating regular Ayón-Beato-García (ABG) black hole (BH) and calculate the center-of-mass (CM) energy for the colliding particles for both extremal and non-extremal cases. It turns out that CM energy depends not only on rotation parameter $a$ but also on charge $Q$. Particularly for the extremal rotating regular ABG BH, CM energy of two colliding particles could be arbitrarily high for critical angular momentum of particles. Furthermore, we also show that, for a non-extremal BH, there e…
We consider anisotropic fluids with directional pressures $p_i = w_i ρ$ ($ρ$ is the density, $w_i = $const, $i = 1,2,3$) as sources of gravity in stationary cylindrically symmetric space-times. We describe a general way of obtaining exact solutions with such sources, where the main features are splitting of the Ricci tensor into static and rotational parts and using the harmonic radial coordinate. Depending on the values of $w_i$, it appears possible to obtain general or special solutions to the Einstein equations, thus recovering some known solutions and finding new ones. Three particular exa…
In this paper we consider rotating modified Hayward and rotating modified Bardeen black holes as particle accelerators. We investigate the center of mass energy of two colliding neutral particles with same rest masses falling from rest at infinity to near the horizons of the mentioned black holes. We investigate the range of the particle's angular momentum and the orbit of the particle. We also investigate the center of mass energy for extremal black hole.
This is the sequel to the first paper of the series, where we have discussed the Hawking radiation from five-dimensional rotating black holes for spin 0, 1/2 and 1 brane fields in the low frequency regime. We consider the emission of a brane localized scalar field from rotating black holes in general space-time dimensions without relying on the low frequency expansions.
We present a family of new rotating black hole solutions to Einstein's equations that generalizes the Kerr-Newman spacetime to include an anisotropic matter. The geometry is obtained by employing the Newman-Janis algorithm. In addition to the mass, the charge and the angular momentum, an additional hair exists thanks to the negative radial pressure of the anisotropic matter. The properties of the black hole are analyzed in detail including thermodynamics. This black hole can be used as a better engine than the Kerr-Newman one in extracting energy.
We obtain the shadow cast induced by the rotating black hole with an anisotropic matter. A Killing tensor representing the hidden symmetry is derived explicitly. The existence of separability structure implies a complete integrability of the geodesic motion. We analyze an effective potential around the unstable circular photon orbits to show that one side of the black hole is brighter than the other side. Further, it is shown that the inclusion of the anisotropic matter ($Kr^{2(1-w)}$) has an effect on the observables of the shadow cast. The shadow observables include approximate shadow radius…
Due to the gravitational lensing effect, a black hole casts a shadow larger than its horizon over a bright background, and the shape and size can be calculated. The Event Horizon Telescope collaboration has produced the first direct image (shadow) of the black hole and it is in accordance with the shadow of a Kerr black hole of general relativity. However, deviations from the Kerr black hole arising from modified theories of gravity are not ruled out and they are important as they offer an arena to test these theories through astrophysical observation. This stimulates us to investigate rotatin…
General relativity predicts that the inner horizon of an astronomically realistic rotating black hole is subject to the mass inflation instability. The inflationary instability acts like a gravity-powered particle accelerator of extraordinary power, accelerating accreted streams of particles along the principal outgoing and ingoing null directions at the inner horizon to collision energies that would, if nothing intervened, typically exceed exponentially the Planck energy. The inflationary instability is fueled by ongoing accretion, and is occurring inevitably in essentially every black hole i…
It is known that the center-of-mass energy of the collision of two massive particles following geodesics around a black hole presents a maximum. The maximum energy increases when the black hole is endowed with spin, and for a maximally rotating hole this energy blows up, offering, in principle, a unique probe of fundamental physics. This work extends the latter studies by considering that the colliding particles possess intrinsic angular momentum (spin), described by the Hanson-Regge-Hojman theory of spinning particles. By analyzing planar trajectories of spinning particles around non-rotating…
A black string is a solution of the four-dimensional general relativity in cylindrical symmetric anti-de Sitter (AdS) spacetime pioneered by Lemos [6]. We obtain an exact rotating black string surrounded by quintessence matter in anti-de Sitter (AdS) spacetime and analyze its properties. The solution has an additional parameter $N_q$ due to background quintessence matter and it also depends on quintessence state parameter $w_q$. Our rotating solution encompasses the Lemos black string \cite{Lemos:1994xp}, which can be recovered in the absence of background matter ($N_q=0$). The special case of…
We study collision of particles in the vicinity of a horizon of a weakly magnetized non-rotating black hole. In the presence of the magnetic field innermost stable circular orbits (ISCO) of charged particles can be located close to the horizon. We demonstrate that for a collision of two particles, one of which is charged and revolving at ISCO and the other is neutral and falling from infinity, the maximal collision energy can be high in the limit of strong magnetic field. This effect has some similarity with the recently discussed effect of high center-of-mass energy for collision of particles…
We construct a model of a rotating wormhole made by cutting and pasting two Kerr spacetimes. As a result, we obtain a rotating thin-shell wormhole with exotic matter at the throat. Two candidates for the exotic matter are considered: (i) a perfect fluid; (ii) an anisotropic fluid. We show that a perfect fluid is unable to support a rotating thin-shall wormhole. On the contrary, the anisotropic fluid with the negative energy density can be a source for such a geometry.
It has been suggested that rotating black holes could serve as particle colliders with arbitrarily high center-of-mass energy. Astrophysical limitations on the maximal spin, back-reaction effects and sensitivity to the initial conditions impose severe limits on the likelihood of such collisions.
We study a simple class of time-dependent rotating Ricci-flat cylindrically symmetric spacetime manifolds whose geodesics admit gravitomagnetic jets. The helical paths of free test particles in these jets up and down parallel to the rotation axis are analogous to those of charged particles in a magnetic field. The jets are attractors. The jet speed asymptotically approaches the speed of light. In effect, such source-free spacetime regions act as "gravitomagnetic accelerators".
We find a new rotating black hole in three-dimensional anti-de Sitter space using an anisotropic perfect fluid inspired by the noncommutative black hole. We deduce the thermodynamical quantities of this black hole and compare them with those of a rotating BTZ solution.
A certain type of matter with anisotropic pressures can add to the Reissner-Nordström metric a term proportional to a power of the radial coordinate. Using the standard method of separating variables for the Hamilton-Jacobi equation, we study the shadow of the corresponding rotating solution, obtained through the Newman-Janis algorithm. We define and calculate three observables in order to characterize the position, size and shape of the shadow.
Some models (such as the Skyrme model, a low-energy effective field theory for QCD) suggest that the high-density matter prevailing in neutron star interiors may be significantly anisotropic. Anisotropy is known to affect the bulk properties of nonrotating neutron stars in General Relativity. In this paper we study the effects of anisotropy on slowly rotating stars in General Relativity. We also consider one of the most popular extensions of Einstein's theory, namely scalar-tensor theories allowing for spontaneous scalarization (a phase transition similar to spontaneous magnetization in ferrom…
Starting with generic stationary axially symmetric spacetimes depending on two spacelike isotropic orthogonal coordinates $x^{1}, x^{2}$, we build anisotropic fluids with and without heat flow but with wanishing viscosity. In the first part of the paper, after applying the transformation $x^1\rightarrow J(x^1)$, $x^2\rightarrow F(x^2)$(with $J(x^1), F(x^2)$ regular functions) to general metrics coefficients $g_{ab}(x^1,x^2)\rightarrow g_{ab}(J(x^1), F(x^2))$ with $G_{x^1 x^2}=0$, being $G_{ab}$ the Einstein's tensor, we obtain that ${\tilde{G}}_{x^1 x^2}=0\rightarrow G_{x^1 x^2}(J(x^1),F(x^2))…
Hardware accelerators (such as Nvidia's CUDA GPUs) have tremendous promise for computational science, because they can deliver large gains in performance at relatively low cost. In this work, we focus on the use of Nvidia's Tesla GPU for high-precision (double, quadruple and octal precision) numerical simulations in the area of black hole physics -- more specifically, solving a partial-differential-equation using finite-differencing. We describe our approach in detail and present the final performance results as compared with a single-core desktop processor and also the Cell BE. We obtain mixe…
In a stationary spacetime $S$ consider a pair of free falling particles that collide with the energy $E_{\rm c.m.}$ (as measured in the center-of-mass system). Let the metric of $S$ or/and the trajectories of the particles depend on a parameter $ k$. Then $S$ is said to be a "(super) accelerator" if $E_{\rm c.m.}$ grows unboundedly with $ k$, even though the energies of the particles at infinity remain bounded. The existence of naturally occurring super accelerators would make it possible to observe otherwise inaccessible phenomena. This is why in recent years a lot of spacetimes were tested o…
Rapidly rotating Kerr black holes can accelerate particles to arbitrarily high energy if the angular momentum of the particle is fine-tuned to some critical value. This phenomenon is robust as it is founded on the basic properties of geodesic orbits around a near-extremal Kerr black hole. On the other hand, the maximum energy of the acceleration is subjected to several physical effects. There is convincing evidence that the particle acceleration to arbitrarily high energy is one of the universal properties of general near-extremal black holes. We also discuss gravitational particle acceleratio…
We consider collision of two particles near the horizon of a nonextremal static black hole. At least one of them is accelerated. We show that the energy $E_{c.m.}$ in the center of mass can become unbounded in spite of the fact that a black hole is neither rotating nor electrically charged. In particular, this happens even for the Schwarzschild black hole. The key ingredient that makes it possible is the presence of positive acceleration (repulsion). Then, if one of particles is fine-tuned properly, the effect takes place. This acceleration can be caused by an external force in the case of par…
A unified approach to regular interiors of black holes with smooth matter distributions in the core region is given. The approach is based on a class of Kerr-Schild metrics representing minimal deformations of the Kerr-Newman solution, and allows us to give a common treatment for (charged and uncharged) rotating and nonrotating black holes. It is shown that the requirement of smoothness of the source constraints the structure of the core region in many respects: in particular, for Schwarzschild holes a de Sitter core can be selected, which is surrounded by a smooth shell giving a leading contr…
Focusing on the rotating black hole (BH) surrounded by the anisotropic fluid matters; radiation, dust, and dark matter, we study the massive scalar superradiant scattering and the stability in the Kiselev spacetime. Superradiance behavior is dependent on the intensity parameter of the anisotropic matter $K$ in the Kiselev spacetime. By adopting the manifest of low-frequency and low-mass for the scalar perturbation, we find $K<0$ enhances the superradiance scattering within the broader frequency range, compared to $K=0$ while $K>0$ suppresses within the narrower frequency range. As a result, th…
We investigate the observational effects of a quintessence model in an anisotropic spacetime. The anisotropic metric is a non-rotating particular case of a generalized Godel's metric and is classified as Bianchi III. This metric is an exact solution of the Einstein-Klein-Gordon field equations with an anisotropic scalar field, which is responsible for the anisotropy of the spacetime geometry. We test the model against observations of type Ia supernovae, analyzing the SDSS dataset calibrated with the MLCS2k2 fitter, and the results are compared to standard quintessence models with Ratra-Peebles…
We investigate here the particle acceleration by Kerr naked singularities. We consider a collision between particles dropped in from infinity at rest, which follow geodesic motion in the equatorial plane, with their angular momenta in an appropriate finite range of values. When an event horizon is absent, an initially infalling particle turns back as an outgoing particle, when it has the angular momentum in an appropriate range of values, which then collides with infalling particles. When the collision takes place close to what would have been the event horizon in the extremal case, the center…
