scholarly journals Blandford-Znajek mechanism in the general stationary axially-symmetric black-hole spacetime

2021 ◽  
Vol 2021 (12) ◽  
pp. 002
Author(s):  
R.A. Konoplya ◽  
J. Kunz ◽  
A. Zhidenko
Keyword(s):  
Black Hole ◽  
Deformation Parameter ◽  
Rotation Parameter ◽  
Energy Extraction ◽  
Axially Symmetric ◽  
Asymptotically Flat ◽  
Kerr Spacetime ◽  
Black Hole Spacetime ◽  
Symmetric Black Hole ◽  
The Magnetic Field

Abstract We consider the Blandford-Znajek process of electromagnetic extraction of energy from a general axially symmetric asymptotically flat slowly rotating black hole. Using the general parametrization of the black-hole spacetime we construct formulas for the flux of the magnetic field and the rate of energy extraction, which are valid not only for the Kerr spacetime, but also for its arbitrary axially symmetric deformations. We show that in the dominant order these quantities depend only on a single deformation parameter, which relates the spin frequency of a black hole with its rotation parameter.

scholarly journals High-energy collision of particles in the magnetic field far from black holes

2014 ◽  
Vol 29 (29) ◽  
pp. 1450151
Author(s):  
O. B. Zaslavskii
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Center Of Mass ◽  
High Energy ◽  
Axially Symmetric ◽  
High Energy Collision ◽  
Mass Frame ◽  
Symmetric Black Hole ◽  
Rotating Star ◽  
The Magnetic Field

We consider collision of two particles in the axially symmetric black hole metric in the magnetic field. If the value of the angular momentum |L| of one particles grows unbound (but its Killing energy remains fixed) one can achieve unbound energy in the center-of-mass frame E c.m. In the absence of the magnetic field, collision of this kind is known to happen in the ergoregion. However, if the magnetic field strength B is also large, with the ratio |L|/B being finite, large E c.m. can be achieved even far from a black hole, in the almost flat region. Such an effect also occurs in the metric of a rotating star.

scholarly journals Thermal behavior of a radially deformed black hole spacetime

2021 ◽  
Vol 81 (5) ◽  
Author(s):  
Subhajit Barman ◽  
Sajal Mukherjee
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Asymptotic Behavior ◽  
Thermal Behavior ◽  
Deformation Parameter ◽  
Radial Deformation ◽  
Hawking Effect ◽  
Enhancing Effect ◽  
Kerr Spacetime ◽  
Black Hole Spacetime

AbstractIn the present article, we study the Hawking effect and the bounds on greybody factor in a spacetime with radial deformation. This deformation is expected to carry the imprint of a non-Einsteinian theory of gravity, but shares some of the important characteristics of general relativity (GR). In particular, this radial deformation will restore the asymptotic behavior, and also allows for the separation of the scalar field equation in terms of the angular and radial coordinates – making it suitable to study the Hawking effect and greybody factors. However, the radial deformation would introduce a change in the locations of the horizon, and therefore, the temperature of the Hawking effect naturally alters. In fact, we observe that the deformation parameter has an enhancing effect on both temperature and bounds on the greybody factor, which introduces a useful distinction with the Kerr spacetime. We discuss these effects elaborately, and broadly study the thermal behavior of a radially deformed spacetime.

scholarly journals Bumblebee gravity with a Kerr–Sen like solution and its Shadow

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Sohan Kumar Jha ◽  
Anisur Rahaman
Keyword(s):  
Black Hole ◽  
Emission Rate ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Field Vector ◽  
Axially Symmetric ◽  
System A ◽  
Black Hole Spacetime ◽  
Symmetric Black Hole ◽  
Careful Investigation

AbstractWe have considered the bumblebee gravity model where lorentz-violating (LV) scenario gets involved through a bumblebee field vector field $$B_\mu $$ B μ . A spontaneous symmetry breaking allows the field to acquires a vacuum expectation value that generates LV into the system. A Kerr–Sen-like solution has been found out starting from the generalized form of a radiating stationery axially symmetric black hole metric. We compute the effective potential offered by the null geodesics in the bumblebee rotating black hole spacetime. The shadow has been sketched for different variations of the parameters involved in the system. A careful investigation has been carried out to study how the shadow gets affected when Lorentz violation enters into the picture. The emission rate of radiation has also been studied and how it varies with the LV parameter $$\ell $$ ℓ is studied scrupulously.

Effect of charge and deformation parameter on energy extraction in charged non-Kerr black holes

2019 ◽  
Vol 28 (16) ◽  
pp. 2040012
Author(s):  
Rehana Rahim ◽  
Khalid Saifullah
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Deformation Parameter ◽  
High Efficiency ◽  
Process Efficiency ◽  
Energy Extraction ◽  
Penrose Process ◽  
Kerr Black Holes ◽  
Very High

We analyze the charged Johannsen–Psaltis black hole for energy extraction via the Penrose process. Efficiency of the Penrose process is found to be dependent on the deformation parameter of the metric and charge. Doing the calculations numerically, we find that, in the nonextremal limit, presence of charge leads to lesser efficiency than the Kerr. In the extremal cases with negative deformation parameter, charge leads to a very high efficiency, higher than that of the Kerr and Johannsen–Psaltis black holes.

scholarly journals Connection between Sinc Approximation for High-Energy Absorption Cross Section and Shadow of Black Holes

2021 ◽  
Author(s):  
Ali Övgün
Keyword(s):  
Black Hole ◽  
Energy Absorption ◽  
Cross Section ◽  
Absorption Cross Section ◽  
High Energy ◽  
Absorption Cross ◽  
Sinc Approximation ◽  
Black Hole Spacetime ◽  
Symmetric Black Hole ◽  
High Energy Absorption

This letter aims to show the connection between the sinc approximation for high-energy absorption cross section and the shadow radius of the spherically symmetric black hole. This connection can give a physical interpretation of the absorption cross section in the eikonal limit parameters. Moreover, the use of this alternative way, one can extract its shadow radius from the absorption cross section in high energy limits to gain more information about the black hole spacetime. Our results indicate that the increasing the value of the shadow radius of the black hole, exponentially increase the the absorption cross section of the black hole in high-energy limits which can be captured by the Event Horizon Telescope (EHT) collaboration.

scholarly journals RELXILL_NK: A Black Hole Relativistic Reflection Model for Testing General Relativity

Proceedings ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 7 ◽  
Author(s):  
Askar B. Abdikamalov ◽  
Dimitry Ayzenberg ◽  
Cosimo Bambi  ◽  
Sourabh Nampalliwar
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Relativistic Effects ◽  
Asymptotically Flat ◽  
X Ray ◽  
Black Hole Accretion ◽  
Reflection Model ◽  
Black Hole Spacetime ◽  
General Relativistic ◽  
Hole Accretion

In this paper, we briefly present RELXILL_NK, the first and currently only readily available model of the relativistic reflection spectrum of black hole accretion disks that includes non-Kerr solutions for the black hole spacetime, thus allowing for tests of the Kerr hypothesis and general relativity (GR). RELXILL_NK makes use of a general relativistic ray-tracing code to calculate the relativistic effects of any well-behaved, stationary, axisymmetric, and asymptotically flat black hole spacetime, while the disk physics is handled through the non-relativistic X-ray reflection code XILLVER. A number of different flavors are available within RELXILL_NK; we summarize and compare these flavors using the Johannsen metric for the black hole spacetime.

scholarly journals Two mass conjectures on axially symmetric black hole-disk systems

2019 ◽  
Vol 99 (2) ◽  
Author(s):  
Wojciech Kulczycki ◽  
Patryk Mach ◽  
Edward Malec
Keyword(s):  
Black Hole ◽  
Axially Symmetric ◽  
Symmetric Black Hole

scholarly journals First law of black hole in the gravitational electromagnetic system

2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Jie Jiang ◽  
Aofei Sang ◽  
Ming Zhang
Keyword(s):  
Black Hole ◽  
Black Hole Thermodynamics ◽  
Effective Theory ◽  
Quantum Corrections ◽  
Maxwell Theory ◽  
Electromagnetic System ◽  
Asymptotically Flat ◽  
First Law Of Thermodynamics ◽  
Bifurcation Surface ◽  
Symmetric Black Hole

Abstract After considering the quantum corrections of Einstein-Maxwell theory, the effective theory will contain some higher-curvature terms and nonminimally coupled electromagnetic fields. In this paper, we study the first law of black holes in the gravitational electromagnetic system with the Lagrangian ℒ(gab, Rabcd, Fab). Firstly, we calculate the Noether charge and the variational identity in this theory, and then generically derive the first law of thermodynamics for an asymptotically flat stationary-axisymmetric symmetric black hole without the requirement that the electromagnetic field is smooth on the bifurcation surface. Our results indicate that the first law of black hole thermodynamics might be valid for the Einstein-Maxwell theory with some quantum corrections in the effective region.

scholarly journals KERR–NEWMAN SOLUTION AND ENERGY IN TELEPARALLEL EQUIVALENT OF EINSTEIN THEORY

2007 ◽  
Vol 22 (14) ◽  
pp. 1047-1056 ◽  
Author(s):  
GAMAL G. L. NASHED
Keyword(s):  
Black Hole ◽  
Vector Field ◽  
Symmetric Solution ◽  
Gravitational Energy ◽  
Rotation Parameter ◽  
Axially Symmetric ◽  
Einstein Theory ◽  
Newman Black Hole ◽  
Charge Parameter ◽  
Electromagnetic Vector Potential

An exact charged axially symmetric solution of the coupled gravitational and electromagnetic fields in the teleparallel equivalent of Einstein theory is derived. It is characterized by three parameters "the gravitational mass M, the charge parameter Q and the rotation parameter a" and its associated metric gives Kerr–Newman spacetime. The parallel vector field and the electromagnetic vector potential are axially symmetric. We then calculate the total energy using the gravitational energy–momentum. The energy is found to be shared by its interior as well as exterior. Switching off the charge parameter we find that no energy is shared by the exterior of the Kerr–Newman black hole.

scholarly journals Quasi-normal modes of near-extremal black holes in generalized spherically symmetric spacetime and strong cosmic censorship conjecture

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
Piyabut Burikham ◽  
Supakchai Ponglertsakul ◽  
Taum Wuthicharn
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Normal Modes ◽  
Cosmic Censorship ◽  
Analytic Formula ◽  
Spherically Symmetric ◽  
Black Hole Background ◽  
Strong Cosmic Censorship ◽  
Black Hole Spacetime ◽  
Symmetric Black Hole

AbstractA number of near-extremal conditions are utilized to simplify the equation of motion of the neutral scalar perturbations in generalized spherically symmetric black hole background into a differential equation with the Pöschl–Teller potential. An analytic formula for quasinormal frequencies is obtained. The analytic formula is then used to investigate strong cosmic censorship conjectures (SCC) of the generalized black hole spacetime for the smooth initial data. The Christodoulou version of the SCC is found to be violated for certain regions of the black hole parameter space including the black holes in general relativity while the $$C^{1}$$ C 1 version of the SCC is always valid.

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