scholarly journals Inner horizon instability and the unstable cores of regular black holes

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Raúl Carballo-Rubio ◽  
Francesco Di Filippo ◽  
Stefano Liberati ◽  
Costantino Pacilio ◽  
Matt Visser
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Quantum Gravity ◽  
Inner Core ◽  
Singularity Problem ◽  
Regular Black Holes ◽  
Black Hole Spacetimes ◽  
Stellar Collapse ◽  
Inner Horizon ◽  
Linear Perturbations

Abstract Regular black holes with nonsingular cores have been considered in several approaches to quantum gravity, and as agnostic frameworks to address the singularity problem and Hawking’s information paradox. While in a recent work we argued that the inner core is destabilized by linear perturbations, opposite claims were raised that regular black holes have in fact stable cores. To reconcile these arguments, we discuss a generalization of the geometrical framework, originally applied to Reissner-Nordtsröm black holes by Ori, and show that regular black holes have an exponentially growing Misner-Sharp mass at the inner horizon. This result can be taken as an indication that stable nonsingular black hole spacetimes are not the definitive endpoint of a quantum gravity regularization mechanism, and that nonperturbative backreation effects must be taken into account in order to provide a consistent description of the quantum-gravitational endpoint of gravitational stellar collapse.

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 Massive Gravitational Waves from Black Hole Inspirals in Quantum Gravity

2018 ◽  
Vol 191 ◽  
pp. 07003
Author(s):  
Xavier Calmet ◽  
Boris Latosh
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Quantum Gravity ◽  
Gravitational Waves ◽  
Emission Rate ◽  
New States ◽  
Model Independent ◽  
Classical Fields ◽  
Using Data

We show that alongside the already observed gravitational waves, quantum gravity predicts the existence of two additional massive classical fields and thus two new massive waves. We set a limit on their masses using data from Eöt-Wash-like experiments. We point out that the existence of these new states is a model independent prediction of quantum gravity. We explain how these new classical fields could impact astrophysical processes and in particular the binary inspirals of black holes. We calculate the emission rate of these new states in binary inspirals astrophysical processes.

scholarly journals Mimicking Black Holes in General Relativity

2021 ◽  
Author(s):  
Thomas Berry
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Thin Shell ◽  
Classical General Relativity ◽  
Regular Black Hole ◽  
Regular Black Holes ◽  
Traversable Wormholes ◽  
Hole Model ◽  
Linearised Stability

<p><b>The central theme of this thesis is the study and analysis of black hole mimickers. The concept of a black hole mimicker is introduced, and various mimicker spacetime models are examined within the framework of classical general relativity. The mimickers examined fall into the classes of regular black holes and traversable wormholes under spherical symmetry. The regular black holes examined can be further categorised as static spacetimes, however the traversable wormhole is allowed to have a dynamic (non-static) throat. Astrophysical observables are calculated for a recently proposed regular black hole model containing an exponential suppression of the Misner-Sharp quasi-local mass. This same regular black hole model is then used to construct a wormhole via the "cut-and-paste" technique. The resulting wormhole is then analysed within the Darmois-Israel thin-shell formalism, and a linearised stability analysis of the (dynamic) wormhole throat is undertaken. Yet another regular black hole model spacetime is proposed, extending a previous work which attempted to construct a regular black hole through a quantum "deformation" of the Schwarzschild spacetime. The resulting spacetime is again analysed within the framework of classical general relativity. </b></p><p>In addition to the study of black hole mimickers, I start with a brief overview of the theory of special relativity where a new and novel result is presented for the combination of relativistic velocities in general directions using quaternions. This is succeed by an introduction to concepts in differential geometry needed for the successive introduction to the theory of general relativity. A thorough discussion of the concept of spacetime singularities is then provided, before analysing the specific black hole mimickers discussed above.</p>

scholarly journals Supermassive black holes surrounded by dark matter modeled as anisotropic fluid: epicyclic oscillations and their fitting to observed QPOs

2021 ◽  
Vol 2021 (11) ◽  
pp. 059
Author(s):  
Z. Stuchlík ◽  
J. Vrba
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Black Hole Spacetimes ◽  
Test Particles

Abstract Recently introduced exact solution of the Einstein gravity coupled minimally to an anisotropic fluid representing dark matter can well represent supermassive black holes in galactic nuclei with realistic distribution of dark matter around the black hole, given by the Hernquist-like density distribution. For these fluid-hairy black hole spacetimes, properties of the gravitational radiation, quasinormal ringing, and optical phenomena were studied, giving interesting results. Here, using the range of physical parameters of these spacetimes allowing for their relevance in astrophysics, we study the epicyclic oscillatory motion of test particles in these spacetimes. The frequencies of the orbital and epicyclic motion are applied in the epicyclic resonance variant of the geodesic model of quasiperiodic oscillations (QPOs) observed in active galactic nuclei to demonstrate the possibility to solve the cases where the standard vacuum black hole spacetimes are not allowing for explanation of the observed data. We demonstrate that the geodesic model can explain the QPOs observed in most of the active galactic nuclei for the fluid-hairy black holes with reasonable halo parameters.

scholarly journals A PROPOSAL TO RESOLVE THE BLACK HOLE INFORMATION PARADOX

2002 ◽  
Vol 11 (10) ◽  
pp. 1537-1540 ◽  
Author(s):  
SAMIR D. MATHUR
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
String Theory ◽  
Quantum Gravity ◽  
Bound State ◽  
Nonlocal Effects ◽  
Information Paradox ◽  
Microscopic Scale ◽  
Gravity Effects ◽  
Black Hole Information

The entropy and information puzzles arising from black holes cannot be resolved if quantum gravity effects remain confined to a microscopic scale. We use concrete computations in nonperturbative string theory to argue for three kinds of nonlocal effects that operate over macroscopic distances. These effects arise when we make a bound state of a large number of branes, and occur at the correct scale to resolve the paradoxes associated with black holes.

Dynamical black holes

2020 ◽  
pp. 312-336
Author(s):  
Piotr T. Chruściel
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Cauchy Data ◽  
Einstein Equations ◽  
Black Hole Spacetimes ◽  
Alternative Approaches ◽  
Definition Of ◽  
Meaningful Definition ◽  
Stability Results ◽  
Black Hole Solutions

In this chapter we review what is known about dynamical black hole-solutions of Einstein equations. We discuss the Robinson–Trautman black holes, with or without a cosmological constant. We review the Cauchy-data approach to the construction of black-hole spacetimes. We propose some alternative approaches to a meaningful definition of black hole in a dynamical spacetime, and we review the nonlinear stability results for black-hole solutions of vacuum Einstein equations.

scholarly journals A proof of the strong cosmic censorship conjecture

2020 ◽  
Vol 29 (14) ◽  
pp. 2042003
Author(s):  
Shahar Hod
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Second Law Of Thermodynamics ◽  
Cosmic Censorship ◽  
Necessary Condition ◽  
Deterministic Theory ◽  
Black Hole Spacetimes ◽  
Generalized Second Law ◽  
Strong Cosmic Censorship ◽  
Cosmic Censorship Conjecture

The Penrose strong cosmic censorship conjecture asserts that Cauchy horizons inside dynamically formed black holes are unstable to remnant matter fields that fall into the black holes. The physical importance of this conjecture stems from the fact that it provides a necessary condition for general relativity to be a truly deterministic theory of gravity. Determining the fate of the Penrose conjecture in nonasymptotically flat black hole spacetimes has been the focus of intense research efforts in recent years. In this paper, we provide a remarkably compact proof, which is based on Bekenstein’s generalized second law of thermodynamics, for the validity of the intriguing Penrose conjecture in physically realistic (dynamically formed) curved black hole spacetimes.

scholarly journals Further evidence for the non-existence of a unified hoop conjecture

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
Shahar Hod
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Critical Mass ◽  
Compact Object ◽  
Compact Objects ◽  
Necessary Condition ◽  
Adm Mass ◽  
Black Hole Spacetimes ◽  
Opposite Inequality ◽  
Hoop Conjecture

AbstractThe hoop conjecture, introduced by Thorne almost five decades ago, asserts that black holes are characterized by the mass-to-circumference relation $$4\pi {\mathcal {M}}/{\mathcal {C}}\ge 1$$ 4 π M / C ≥ 1 , whereas horizonless compact objects are characterized by the opposite inequality $$4\pi {\mathcal {M}}/{\mathcal {C}}<1$$ 4 π M / C < 1 (here $${\mathcal {C}}$$ C is the circumference of the smallest ring that can engulf the self-gravitating compact object in all azimuthal directions). It has recently been proved that a necessary condition for the validity of this conjecture in horizonless spacetimes of spatially regular charged compact objects is that the mass $${\mathcal {M}}$$ M be interpreted as the mass contained within the engulfing sphere (and not as the asymptotically measured total ADM mass). In the present paper we raise the following physically intriguing question: is it possible to formulate a unified version of the hoop conjecture which is valid for both black holes and horizonless compact objects? In order to address this important question, we analyze the behavior of the mass-to-circumference ratio of Kerr–Newman black holes. We explicitly prove that if the mass $${\mathcal {M}}$$ M in the hoop relation is interpreted as the quasilocal Einstein–Landau–Lifshitz–Papapetrou and Weinberg mass contained within the black-hole horizon, then these charged and spinning black holes are characterized by the sub-critical mass-to-circumference ratio $$4\pi {\mathcal {M}}/{\mathcal {C}}<1$$ 4 π M / C < 1 . Our results provide evidence for the non-existence of a unified version of the hoop conjecture which is valid for both black-hole spacetimes and spatially regular horizonless compact objects.

scholarly journals Quantum leaps of black holes: Magnifying glasses of quantum gravity

2016 ◽  
Vol 25 (12) ◽  
pp. 1644024 ◽  
Author(s):  
Sumanta Chakraborty ◽  
Kinjalk Lochan
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Quantum Gravity ◽  
The Third

We show using simple arguments, that the conceptual triad of a classical black hole, semi-classical Hawking emission and geometry quantization is inherently, mutually incompatible. Presence of any two explicitly violates the third. We argue that geometry quantization, if realized in nature, magnifies the quantum gravity features hugely to catapult them into the realm of observational possibilities. We also explore a quantum route towards extremality of the black holes.

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