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 ENERGY EXTRACTION FROM GRAVITATIONAL COLLAPSE TO STATIC BLACK HOLES

2003 ◽  
Vol 12 (01) ◽  
pp. 121-127 ◽  
Author(s):  
REMO RUFFINI ◽  
LUCA VITAGLIANO
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Extraction Process ◽  
Maximum Efficiency ◽  
Energy Extraction ◽  
Mass Energy ◽  
Classical Level ◽  
Static Black Hole ◽  
Exact Analytic Expression ◽  
Analytic Expression

The mass-energy formula of black holes implies that up to 50% of the energy can be extracted from a static black hole. Such a result is reexamined using the recently established analytic formulas for the collapse of a shell and the expression for the irreducible mass of a static black hole. It is shown that the efficiency of energy extraction process during the formation of the black hole is linked in an essential way to the gravitational binding energy, the formation of the horizon and the reduction of the kinetic energy of implosion. Here a maximum efficiency of 50% in the extraction of the mass energy is shown to be generally attainable in the collapse of a spherically symmetric shell: surprisingly this result holds as well in the two limiting cases of the Schwarzschild and extreme Reissner–Nordström space–times. Moreover, the analytic expression recently found for the implosion of a spherical shell to an already formed black hole leads to a new exact analytic expression for the energy extraction which results in an efficiency strictly less than 100% for any physical implementable process. There appears to be no incompatibility between General Relativity and Thermodynamics at this classical level.

scholarly journals Fermat’s principle in black-hole spacetimes

2018 ◽  
Vol 27 (14) ◽  
pp. 1847025 ◽  
Author(s):  
Shahar Hod
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Black Hole Spacetimes ◽  
Fermat’S Principle ◽  
Kerr Black Holes ◽  
Fermat's Principle ◽  
Asymptotic Observers

Black-hole spacetimes are known to possess closed light rings. We here present a remarkably compact theorem which reveals the physically intriguing fact that these unique null circular geodesics provide the fastest way, as measured by asymptotic observers, to circle around spinning Kerr black holes.

scholarly journals Black hole superradiance as a probe of ultra-light new particles

2016 ◽  
Vol 12 (S324) ◽  
pp. 273-278
Author(s):  
Robert Lasenby
Keyword(s):  
Beyond Standard Model ◽  
Black Holes ◽  
Black Hole ◽  
Standard Model ◽  
Gravitational Wave ◽  
Exponential Growth ◽  
Gravitational Radiation ◽  
Bound States ◽  
Penrose Process ◽  
Energy And Momentum

AbstractBosonic fields around a spinning black hole can be amplified via ‘superradiance’, a wave analogue of the Penrose process, which extracts energy and momentum from the black hole. For hypothetical ultra-light bosons, with Compton wavelengths on ≳ km scales, such a process can lead to the exponential growth of gravitationally bound states around astrophysical Kerr black holes. If such particles exist, as predicted in many theories of beyond Standard Model physics, then these bosonic clouds give rise to a number of potentially-observable signals. Among the most promising are monochromatic gravitational radiation signals which could be detected at Advanced LIGO and future gravitational wave observatories.

scholarly journals Central charges for AdS black holes

2021 ◽  
Author(s):  
Malcolm Perry ◽  
Maria J Rodriguez
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Cosmological Constant ◽  
Central Charge ◽  
Negative Cosmological Constant ◽  
Ads Black Holes ◽  
Kerr Black Holes ◽  
Distinguishing Features ◽  
Area Law ◽  
Cardy Formula

Abstract Nontrivial diffeomorphisms act on the horizon of a generic 4D black holes and create distinguishing features referred to as soft hair. Amongst these are a left-right pair of Virasoro algebras with associated charges that reproduce the Bekenstein-Hawking entropy for Kerr black holes. In this paper we show that if one adds a negative cosmological constant, there is a similar set of infinitesimal diffeomorphisms that act non-trivially on the horizon. The algebra of these diffeomorphisms gives rise to a central charge. Adding a boundary counterterm, justified to achieve integrability, leads to well-defined central charges with cL = cR. The macroscopic area law for Kerr-AdS black holes follows from the assumption of a Cardy formula governing the black hole microstates.

scholarly journals Massive scalar field perturbation on Kerr black holes in dynamical Chern–Simons gravity

2021 ◽  
Vol 81 (5) ◽  
Author(s):  
Shao-Jun Zhang
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Scalar Field ◽  
Massive Scalar ◽  
Coupling Constant ◽  
Field Mass ◽  
Field Perturbation ◽  
Massive Scalar Field ◽  
Kerr Black Holes ◽  
Chern Simons

AbstractWe study massive scalar field perturbation on Kerr black holes in dynamical Chern–Simons gravity by performing a $$(2+1)$$ ( 2 + 1 ) -dimensional simulation. Object pictures of the wave dynamics in time domain are obtained. The tachyonic instability is found to always occur for any nonzero black hole spin and any scalar field mass as long as the coupling constant exceeds a critical value. The presence of the mass term suppresses or even quench the instability. The quantitative dependence of the onset of the tachyonic instability on the coupling constant, the scalar field mass and the black hole spin is given numerically.

scholarly journals Shocks in relativistic viscous accretion flows around Kerr black holes

2019 ◽  
Vol 488 (2) ◽  
pp. 2412-2422 ◽  
Author(s):  
Indu K Dihingia ◽  
Santabrata Das ◽  
Debaprasad Maity ◽  
Anuj Nandi
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Shock Front ◽  
Critical Point ◽  
Parameter Space ◽  
Accretion Flows ◽  
Flow Parameters ◽  
Flow Motion ◽  
Present Formalism ◽  
Kerr Black Holes

ABSTRACT We study the relativistic viscous accretion flows around the Kerr black holes. We present the governing equations that describe the steady-state flow motion in full general relativity and solve them in 1.5D to obtain the complete set of global transonic solutions in terms of the flow parameters, namely specific energy (${\mathcal E}$), specific angular momentum (${\mathcal L}$), and viscosity (α). We obtain a new type of accretion solution which was not reported earlier. Further, we show for the first time to the best of our knowledge that viscous accretion solutions may contain shock waves particularly when flow simultaneously passes through both inner critical point (rin) and outer critical point (rout) before entering into the Kerr black holes. We examine the shock properties, namely shock location (rs) and compression ratio (R, the measure of density compression across the shock front) and show that shock can form for a large region of parameter space in ${\cal L}\!-\!{\cal E}$ plane. We study the effect of viscous dissipation on the shock parameter space and find that parameter space shrinks as α is increased. We also calculate the critical viscosity parameter (αcri) beyond which standing shock solutions disappear and examine the correlation between the black hole spin (ak) and αcri. Finally, the relevance of our work is conferred where, using rs and R, we empirically estimate the oscillation frequency of the shock front (νQPO) when it exhibits quasi-periodic (QP) variations. The obtained results indicate that the present formalism seems to be potentially viable to account for the QPO frequency in the range starting from milli-Hz to kilo-Hz as $0.386~{\rm Hz}\le \nu _{\mathrm{ QPO}} (\frac{10\, \mathrm{M}_\odot }{M_{\mathrm{ BH}}}) \le 1312$ Hz for ak = 0.99, where MBH stands for the black hole mass.

scholarly journals How fast can a black hole rotate?

2015 ◽  
Vol 24 (12) ◽  
pp. 1544022 ◽  
Author(s):  
Carlos A. R. Herdeiro ◽  
Eugen Radu
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Mass Formula ◽  
Linear Velocity ◽  
Asymptotically Flat ◽  
Velocity Of Light ◽  
Universal Bound ◽  
Kerr Black Holes

Kerr black holes (BHs) have their angular momentum, [Formula: see text], bounded by their mass, [Formula: see text]: [Formula: see text]. There are, however, known BH solutions violating this Kerr bound. We propose a very simple universal bound on the rotation, rather than on the angular momentum, of four-dimensional, stationary and axisymmetric, asymptotically flat BHs, given in terms of an appropriately defined horizon linear velocity, [Formula: see text]. The [Formula: see text] bound is simply that [Formula: see text] cannot exceed the velocity of light. We verify the [Formula: see text] bound for known BH solutions, including some that violate the Kerr bound, and conjecture that only extremal Kerr BHs saturate the [Formula: see text] bound.

scholarly journals Energy extraction from Kerr black holes by rigidly rotating strings

2016 ◽  
Vol 94 (12) ◽  
Author(s):  
Shunichiro Kinoshita ◽  
Takahisa Igata ◽  
Kentaro Tanabe
Keyword(s):  
Black Holes ◽  
Energy Extraction ◽  
Kerr Black Holes

scholarly journals SEMICLASSICAL CORRECTIONS TO THE CARDY–VERLINDE FORMULA OF KERR BLACK HOLES

2008 ◽  
Vol 23 (13) ◽  
pp. 2047-2053 ◽  
Author(s):  
M. R. SETARE
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Central Charge ◽  
Kerr Black Hole ◽  
Gravitational Effect ◽  
The Self ◽  
Entropy Formula ◽  
Verlinde Formula ◽  
Kerr Black Holes

In this paper, we compute the corrections to the Cardy–Verlinde formula of four-dimensional Kerr black hole. These corrections are considered within the context of KKW analysis and arise as a result of the self-gravitational effect. Then we show that one can take into account the semiclassical corrections of the Cardy–Verlinde entropy formula by only redefining the Virasoro operator L0 and the central charge c.

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