scholarly journals Black Holes or an Objects without Event Horizon?

2021 ◽  
Author(s):  
Leonid Verozub
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Fermi Gas ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
Degenerate Fermi Gas

The paper substantiates the possibility that objects that we usually identify with black holes are self-gravitating, fully or partially degenerate Fermi gas. This follows from the modification of Einstein's equations, which is based on a mathematical fact that the author of the GR could not have known in his time.

scholarly journals Black Holes or an Objects without Event Horizon?

2021 ◽  
Author(s):  
Leonid Verozub
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Fermi Gas ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
Degenerate Fermi Gas

The paper substantiates the possibility that objects that we usually identify with black holes are self-gravitating, fully or partially degenerate Fermi gas. This follows from the modification of Einstein's equations, which is based on a mathematical fact that the author of the GR could not have known in his time.

Gravitation and Black Holes

2020 ◽  
pp. 11-23
Author(s):  
John W. Moffat
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Event Horizon ◽  
Compact Object ◽  
Dense Matter ◽  
Einstein’S Equations ◽  
Einstein's Equations

Einstein’s theory of general relativity introduced the concept of black holes to physics and astronomy. But, eminent physicists such as Einstein and Eddington did not believe in the existence of black holes. Schwarzschild solved Einstein’s equations and disclosed a possible dark compact object with an event horizon. This is a membrane in spacetime surrounding the object, from which nothing can escape, not even light. The chapter describes the contributions of Chandrasekhar, Kruskal, Wheeler, Oppenheimer, Landau, Kerr, and others to help promote black holes in the physics and astronomy communities. It details ideas about the origins of black holes and the conundrums they still present, such as the singularities (infinitely dense matter) associated with them.

Numerical relativity: challenges for computational science

Acta Numerica ◽  
1999 ◽  
Vol 8 ◽  
pp. 1-45 ◽  
Author(s):  
Gregory B. Cook ◽  
Saul A. Teukolsky
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Numerical Relativity ◽  
Hyperbolic Systems ◽  
Nonlinear Partial Differential Equations ◽  
Elliptic Systems ◽  
Computational Domain ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
3 Dimensional

We describe the burgeoning field of numerical relativity, which aims to solve Einstein's equations of general relativity numerically. The field presents many questions that may interest numerical analysts, especially problems related to nonlinear partial differential equations: elliptic systems, hyperbolic systems, and mixed systems. There are many novel features, such as dealing with boundaries when black holes are excised from the computational domain, or how even to pose the problem computationally when the coordinates must be determined during the evolution from initial data. The most important unsolved problem is that there is no known general 3-dimensional algorithm that can evolve Einstein's equations with black holes that is stable. This review is meant to be an introduction that will enable numerical analysts and other computational scientists to enter the field. No previous knowledge of special or general relativity is assumed.

scholarly journals Spherically symmetric black holes and affine-null metric formulation of Einstein’s equations

2021 ◽  
Vol 104 (8) ◽  
Author(s):  
Emanuel Gallo ◽  
Carlos Kozameh ◽  
Thomas Mädler ◽  
Osvaldo M. Moreschi ◽  
Alejandro Perez
Keyword(s):  
Black Holes ◽  
Spherically Symmetric ◽  
Einstein’S Equations ◽  
Einstein's Equations

WEAK SINGULARITIES IN GENERAL RELATIVITY

2002 ◽  
Vol 17 (20) ◽  
pp. 2779-2779
Author(s):  
J. A. VICKERS
Keyword(s):  
Event Horizon ◽  
Cosmic Censorship ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
Non Linear ◽  
Cosmic Censorship Hypothesis ◽  
Interior Points ◽  
Weak Singularities ◽  
Cauchy Development ◽  
Linear Nature

According to the Cosmic Censorship hypothesis realistic singularities should be hidden by an event horizon. However there are many examples of physically realistic space–times which are geodesically incomplete, and hence possess singularities according to the usual definition, which are not inside an event horizon. Many of these counterexamples to the cosmic censorship conjecture have a curvature tensor which is reasonably behaved (for example bounded or integrable) as one approaches the singularity. We give a class of weak singularities which may be described as having distributional curvature1. Because of the non–linear nature of Einstein's equations such distributional geometries are described using a diffeomorphism invariant theory of non–linear generalised functions2. We also investigate the propagation of test fields on space–times with weak singularities. We give a class of singularities3,4 which do not disrupt the Cauchy development of test fields and result in space–times which satisfy Clarke's criterion of 'generalised hyperbolicity'. We consider that points which are well behaved in this way, and where Einstein's equations make sense distributionally, should be regarded as interior points of the space–time rather than counterexamples to cosmic censorship.

scholarly journals On the duality of Schwarzschild-de Sitter spacetime and moving mirror

2022 ◽  
Author(s):  
Diego Fernández-Silvestre ◽  
Joshua Foo ◽  
Michael R.R Good
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Simple Solution ◽  
Particle Spectrum ◽  
Cosmological Horizon ◽  
De Sitter ◽  
Einstein’S Equations ◽  
Relative Temperature ◽  
Einstein's Equations ◽  
Sitter Spacetime

Abstract The Schwarzschild-de Sitter (SdS) metric is the simplest spacetime solution in general relativity with both a black hole event horizon and a cosmological event horizon. Since the Schwarzschild metric is the most simple solution of Einstein's equations with spherical symmetry and the de Sitter metric is the most simple solution of Einstein's equations with a positive cosmological constant, the combination in the SdS metric defines an appropriate background geometry for semi-classical investigation of Hawking radiation with respect to past and future horizons. Generally, the black hole temperature is larger than that of the cosmological horizon, so there is heat flow from the smaller black hole horizon to the larger cosmological horizon, despite questions concerning the definition of the relative temperature of the black hole without a measurement by an observer sitting in an asymptotically flat spacetime. Here we investigate the accelerating boundary correspondence (ABC) of the radiation in SdS spacetime without such a problem. We have solved for the boundary dynamics, energy flux and asymptotic particle spectrum. The distribution of particles is globally non-thermal while asymptotically the radiation reaches equilibrium.

scholarly journals A spherically topological analysis of stationary black holes

2018 ◽  
Vol 1 ◽  
pp. 33-36
Author(s):  
Benjamin Puzantian
Keyword(s):  
Black Holes ◽  
Signal Processing ◽  
Black Hole ◽  
Angular Momentum ◽  
Fourier Analysis ◽  
Event Horizon ◽  
Topological Analysis ◽  
Stationary Black Hole ◽  
Einstein's Equations ◽  
Schwarzschild Metric

A black hole with zero angular momentum is said to be stationary and under certain conditions such a black hole can represented as a sphere. This review examines Hawking’s topology theorem, the Schwarzschild metric, novel solutions to Einstein’s equations, resonances of hyperbolic orbits around the event horizon for spherical, stationary black holes, and analyzes their importance. It is suggested, that in the spherical stationary black hole case, the Fourier analysis can be used to find the resonances due to Geometric scattering of hyperbolic orbits and thus the outgoing energy fields from the event horizon can be found more precisely; allowing for the adequate signal processing analysis to be found for such a field.

Black holes, star clusters, and naked singularities: numerical solution of Einstein’s equations

1992 ◽  
Vol 340 (1658) ◽  
pp. 365-390 ◽  
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Gravitational Field ◽  
Numerical Solution ◽  
Star Clusters ◽  
Particle Simulation ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
Naked Singularities ◽  
Hoop Conjecture

We describe a new method for the numerical solution of Einstein’s equations for the dynamical evolution of a collisionless gas of particles in general relativity. The gravitational field can be arbitrarily strong and particle velocities can approach the speed of light. The computational method uses the tools of numerical relativity and N -body particle simulation to follow the full nonlinear behaviour of these systems. Specifically, we solve the Vlasov equation in general relativity by particle simulation. The gravitational field is integrated by using the 3 + 1 formalism of Arnowitt, Deser and Misner. Physical applications include the stability of relativistic star clusters the binding energy criterion for stability, and the collapse of star clusters to black holes. Astrophysical issues addressed include the possible origin of quasars and active galactic nuclei via the collapse of dense star clusters to supermassive black holes. The method described here also provides a new tool for studying the cosmic censorship hypothesis and the possibility of naked singularities. The formation of a naked singularity during the collapse of a finite object would pose a serious difficulty for the theory of general relativity. The hoop conjecture suggests that this possibility will never happen provided the object is sufficiently compact (≤ M ) in all of its spatial dimensions. But what about the collapse of a long, non-rotating, prolate object to a thin spindle? Such collapse leads to a strong singularity in newtonian gravitation. Using our numerical code to evolve collisionless gas spheroids in full general relativity, we find that in all cases the spheroids collapse to singularities. When the spheroids are sufficiently compact the singularities are hidden inside black holes. However, when the spheroids are sufficiently large there are no apparent horizons. These results lend support to the hoop conjecture and appear to demonstrate that naked singularities can form in asymptotically flat space-times.

scholarly journals Event Horizon Telescope observations of the jet launching and collimation in Centaurus A

2021 ◽  
Author(s):  
Michael Janssen ◽  
Heino Falcke ◽  
Matthias Kadler ◽  
Eduardo Ros ◽  
Maciek Wielgus ◽  
...  
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
Radio Jets ◽  
Long Baseline ◽  
Wide Range ◽  
Terahertz Frequencies ◽  
Source Structure ◽  
Centaurus A

AbstractVery-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg ≡ GM/c2) scales in nearby sources1. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on ~500 rg scales remarkably well. Furthermore, we identify the location of Centaurus A’s SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source’s event horizon shadow4 should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses5,6.

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