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1
Barausse, Enrico. "Black Holes in General Relativity and Beyond." Proceedings 17, no. 1 (June 14, 2019): 1. http://dx.doi.org/10.3390/proceedings2019017001.
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The recent detections of gravitational waves from binary systems of black holes are in remarkable agreement with the predictions of General Relativity. In this pedagogical mini-review, I go through the physics of the different phases of the evolution of black hole binary systems, providing a qualitative physical interpretation of each one of them. I also briefly describe how these phases would be modified if gravitation were described by a theory extending or deforming General Relativity, or if the binary components turned out to be more exotic compact objects than black holes.
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Yadav, Ranjit Prasad. "Theory of General Relativity: Historical Perspective." Academic Voices: A Multidisciplinary Journal 4 (March 28, 2015): 49–52. http://dx.doi.org/10.3126/av.v4i0.12358.
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General relativity was developed by Albert Einstein near about 100 Years ago. This article attempt to give an outline about the brief history of general theory of relativity and to understand the background to the theory we have to look at how theories of gravitation developed. Before the advent of GR, Newton's law of gravitation had been accepted for more than two hundred years as a valid description of the gravitational force between masses i.e. gravity was the result of an attractive force between massive objects. General relativity has developed in to an essential tool in modern astrophysics. It provides the foundation for the understanding of black holes, regions of space where gravitational attraction is strong that not even light can escape and also a part of the big bang model of cosmology.DOI: http://dx.doi.org/10.3126/av.v4i0.12358Academic Voices Vol.4 2014: 49-52
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Will, Clifford M. "The confrontation between general relativity and experiment." Proceedings of the International Astronomical Union 5, S261 (April 2009): 198–99. http://dx.doi.org/10.1017/s174392130999038x.
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AbstractWe review the experimental evidence for Einstein's general relativity. A variety of high precision null experiments confirm the Einstein Equivalence Principle, which underlies the concept that gravitation is synonymous with spacetime geometry, and must be described by a metric theory. Solar system experiments that test the weak-field, post-Newtonian limit of metric theories strongly favor general relativity. Binary pulsars test gravitational-wave damping and aspects of strong-field general relativity. During the coming decades, tests of general relativity in new regimes may be possible. Laser interferometric gravitational-wave observatories on Earth and in space may provide new tests via precise measurements of the properties of gravitational waves. Future efforts using X-ray, infrared, gamma-ray and gravitational-wave astronomy may one day test general relativity in the strong-field regime near black holes and neutron stars.
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Ahmed, Shohel, and Md Showkat Ali. "Numerical Relativity: Solving Geodesics equation for Massive Particle Around Black Holes Horizon." GANIT: Journal of Bangladesh Mathematical Society 35 (June 28, 2016): 79–85. http://dx.doi.org/10.3329/ganit.v35i0.28571.
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General relativity is the most beautiful physical theory ever invented. It describes one of the most pervasive features of the world we experience - gravitation. The gravitational field acts on nearby matter defines by the curvature of space-time. The black holes of nature are the most perfect macroscopic objects there are in the universe that constructed our concept of space-time. In this paper we use Einsteins general relativity to model the motions of massive particles around the two black holes: static and rotating. These equations of motion around black holes will be studied with special focus towards the variation of symmetry by the change of gravitational effect.GANIT J. Bangladesh Math. Soc.Vol. 35 (2015) 79-85
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HOD, SHAHAR. "A SIMPLIFIED TWO-BODY PROBLEM IN GENERAL RELATIVITY." International Journal of Modern Physics D 22, no. 12 (October 2013): 1342029. http://dx.doi.org/10.1142/s0218271813420297.
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General relativity, Einstein's theory of gravity, predicts a universe full of black holes and gravitational waves. The prospects of detecting gravitational waves from inspirals of compact astrophysical objects into supermassive black holes have made it highly important to analyze in detail the gravitational two-body problem. While the two-body problem in Newtonian gravity (the weak-field limit) has a well-defined compact analytic solution, the corresponding problem in general relativity (the strong-field regime) is very complex and cannot be solved analytically. In this paper, we propose to model the two-body problem in general relativity using the analytically solvable model of a ring of particles in orbit around a central black hole. We use our model to calculate the innermost stable circular orbit (ISCO) frequency which characterizes the two-body dynamics. Remarkably, our expression for the characteristic ISCO frequency through linear order in the ring's mass predicts with astonishing accuracy the actual value of this fundamental parameter.
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Lo, C. Y. "The question on the existence of black holes." Physics Essays 34, no. 4 (December 1, 2021): 464–69. http://dx.doi.org/10.4006/0836-1398-34.4.464.
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Simulation shows that general relativity would lead to the existence of black holes if gravitation is always attractive. However, although we observed an invisible and extremely heavy object governs the orbits of stars at the center of our galaxy, we still cannot determine the existence of a black hole. Thus, one may ask whether black holes actually exist. Einstein’s general relativity has been established, because its prediction on the bending of light rays has been confirmed by observation. However, Einstein’s prediction on the increment of weight for a piece of metal as the temperature increases is proven incorrect by experiments, which actually show a reduction of weight. This leads to the necessary existence of repulsive gravitational force, which has been demonstrated by a charged capacitor hovering above the earth. Thus, Einstein, Newton, Galileo, and Maxwell all made the error of overlooking the repulsive gravitational charge-mass interaction. Thus, it is necessary to rejustify the existence of black holes, because gravity is not always attractive. Moreover, repulsive gravitational force makes it necessary to extend general relativity to a five-dimensional theory. Thus, to find out whether black holes exist, it is necessary to investigate the repulsive gravitation and a five-dimensional space.
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Shankaranarayanan, S. "Strong gravity signatures in the polarization of gravitational waves." International Journal of Modern Physics D 28, no. 14 (October 2019): 1944020. http://dx.doi.org/10.1142/s0218271819440206.
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General Relativity is a hugely successful description of gravitation. However, both theory and observations suggest that General Relativity might have significant classical and quantum corrections in the Strong Gravity regime. Testing the strong field limit of gravity is one of the main objectives of the future gravitational wave detectors. One way to detect strong gravity is through the polarization of gravitational waves. For quasi-normal modes of black-holes in General Relativity, the two polarization states of gravitational waves have the same amplitude and frequency spectrum. Using the principle of energy conservation, we show that the polarizations differ for modified gravity theories. We obtain a diagnostic parameter for polarization mismatch that provides a unique way to distinguish General Relativity and modified gravity theories in gravitational wave detectors.
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Eisenstaedt, Jean. "Dark Bodies and Black Holes, Magic Circles and Montgolfiers: Light and Gravitation from Newton to Einstein." Science in Context 6, no. 1 (1993): 83–106. http://dx.doi.org/10.1017/s0269889700001320.
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The ArgumentThe question of the possible existence of black holes is closely related to the question of the action of gravitation on the propagation of light. It has been raised recurrently from the when that Newton referred to a possible bending of light in his Opticks. And it relies on apparently simple questions: Is light subject to gravitation? What is the effect of a gravitational field on the propagation of light? Could a particle of light emitted by a star be retained by its gravitational field?From the end of the 1960s, the black hole idea has had a very important place in the relativistic literature, not to speak of the popularization of the theory. It turned out to be not only an important concept but also a tool that permitted us to understand general relativity better, indeed a tool that contributed greatly to changing the interpretation of Einstein's theory of gravitation. Here too I want to use this concept of the black hole to assist our understanding of the history of general relativity: the black hole is a fundamental milestone in the evolution of general relativity.
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Nashed, Gamal. "Charged and Non-Charged Black Hole Solutions in Mimetic Gravitational Theory." Symmetry 10, no. 11 (November 1, 2018): 559. http://dx.doi.org/10.3390/sym10110559.
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In this study, we derive, in the framework of mimetic theory, charged and non-charged black hole solutions for spherically symmetric as well as flat horizon spacetimes. The asymptotic behavior of those black holes behave as flat or (A)dS spacetimes and coincide with the solutions derived before in general relativity theory. Using the field equations of non-linear electrodynamics mimetic theory we derive new black hole solutions with monopole and quadrupole terms. The quadruple term of those black holes is related by a constant so that its vanishing makes the solutions coincide with the linear Maxwell black holes. We study the singularities of those solutions and show that they possess stronger singularity than the ones known in general relativity. Among many things, we study the horizons as well as the heat capacity to see if the black holes derived in this study have thermodynamical stability or not.
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Thorne, Kip S. "Gravitational Waves from Compact Bodies." Symposium - International Astronomical Union 165 (1996): 153–83. http://dx.doi.org/10.1017/s0074180900055649.
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According to general relativity theory, compact concentrations of energy (e.g., neutron stars and black holes) should warp spacetime strongly, and whenever such an energy concentration changes shape, it should create a dynamically changing spacetime warpage that propagates out through the Universe at the speed of light. This propagating warpage is called gravitational radiation — a name that arises from general relativity's description of gravity as a consequence of spacetime warpage.
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Le Tiec, Alexandre. "The overlap of numerical relativity, perturbation theory and post-Newtonian theory in the binary black hole problem." International Journal of Modern Physics D 23, no. 10 (September 2014): 1430022. http://dx.doi.org/10.1142/s0218271814300225.
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Inspiralling and coalescing binary black holes are promising sources of gravitational radiation. The orbital motion and gravitational-wave emission of such system can be modeled using a variety of approximation schemes and numerical methods in general relativity: The post-Newtonian (PN) formalism, black hole perturbation theory (BHP), numerical relativity (NR) simulations and the effective one-body (EOB) model. We review recent work at the multiple interfaces of these analytical and numerical techniques, emphasizing the use of coordinate-invariant relationships to perform meaningful comparisons. Such comparisons provide independent checks of the validity of the various calculations, they inform the development of a universal, semi-analytical model of the binary dynamics and gravitational-wave emission and they help to delineate the respective domains of validity of each approximation method. For instance, several recent comparisons suggest that perturbation theory may find applications in a broader range of physical problems than previously thought, including the radiative inspiral of intermediate mass-ratio and comparable-mass black hole binaries.
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KIM, Wontae, and Mu-In PARK. "Frontiers of Quantum Black Holes." Physics and High Technology 29, no. 11 (November 30, 2020): 10–16. http://dx.doi.org/10.3938/phit.29.039.
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A black hole is a theoretical prediction of Einstein’s general theory of relativity, differently from Newtonian gravity, which is a non-relativistic gravity. In recent few years, its direct detection via gravitational waves and other multi-messenger observations have made it possible to test the prediction and hence its associated general relativity. From purely theoretical points of view, general relativity cannot be a complete description due to its not being compatible with quantum mechanics, which is a successful description of microscopic objects. In this article, we introduce the conceptional development of quantum-gravity theories and give brief sketches of fundamental problems in quantum black holes. As an interesting model of quantum black holes, we consider a collapsing shell of matter to form a Hayward black hole and investigate semiclassically quantum radiation from the shell. By using the Israel’s formulation and the functional Schrödinger formulation for massless quantum radiation, we find that the Hawking temperature can be deduced from the occupation number of excited states when the shell approaches its own horizon.
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Battista, Emmanuele, and Giampiero Esposito. "What is a reduced boundary in general relativity?" International Journal of Modern Physics D 30, no. 07 (April 8, 2021): 2150050. http://dx.doi.org/10.1142/s0218271821500504.
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The concept of boundary plays an important role in several branches of general relativity, e.g. the variational principle for the Einstein equations, the event horizon and the apparent horizon of black holes, the formation of trapped surfaces. On the other hand, in a branch of mathematics known as geometric measure theory, the usefulness has been discovered long ago of yet another concept, i.e. the reduced boundary of a finite-perimeter set. This paper proposes therefore a definition of finite-perimeter sets and their reduced boundary in general relativity. Moreover, a basic integral formula of geometric measure theory is evaluated explicitly in the relevant case of Euclidean Schwarzschild geometry for the first time in the literature. This research prepares the ground for a measure-theoretic approach to several concepts in gravitational physics, supplemented by geometric insight. Moreover, such an investigation suggests considering the possibility that the in–out amplitude for Euclidean quantum gravity should be evaluated over finite-perimeter Riemannian geometries that match the assigned data on their reduced boundary. As a possible application, an analysis is performed of the basic formulae leading eventually to the corrections of the intrinsic quantum mechanical entropy of a black hole.
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Kenath, Arun, Samartha C. A., and K. A. Chrandrashekaran. "Kerr Black Holes and Jets." Mapana - Journal of Sciences 4, no. 2 (August 15, 2005): 67–74. http://dx.doi.org/10.12723/mjs.7.8.
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during the sen*ster M.E. under the guidance of Prof. C Sivarorn, We are very thankful to Prof. C. for his guidance out and hoi. K. A Q•androshekor, H. O O, PG Dept Physics. Christ for and encouragement. Black holes A is a of pace-time that rTWSS in it that there is no way for a nearby object iO escape its gravitational pun. Since Our best thory of gravity Of the moment is Einstein' s general theory oi relativity, we have delve into some results Of this theory to understand black holes in The basic associated With 0 block hole is its Schwarzschild radius.
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Stavrinos, Panayiotis, and Emmanuel Saridakis. "Editorial of Modified Theories of Gravity and Cosmological Applications." Universe 8, no. 8 (August 9, 2022): 415. http://dx.doi.org/10.3390/universe8080415.
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General Relativity is a theory of gravity that describes some of the effects of gravity with high accuracy, such as solar system tests, gravitational lensing, gravitational waves, black holes, deflection angle, etc., in a definite framework of an homogeneous and isotropic space–time[...]
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Srivastava, Dr Shailendra Kumar. "An Approach to Colliding Plane Waves in General Relativity." International Journal for Research in Applied Science and Engineering Technology 9, no. 12 (December 31, 2021): 981–88. http://dx.doi.org/10.22214/ijraset.2021.39397.
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Abstract: For many years after Einstein proposed his general theory of relativity, only a few exact solutions were known. Today the situation is completely different, and we now have a vast number of such solutions. However, very few are well understood in the sense that they can be clearly interpreted as the fields of real physical sources. The obvious exceptions are the Schwarzschild and Kerr solutions. These have been very thoroughly analysed, and clearly describe the gravitational fields surrounding static and rotating black holes respectively. In practice, one of the great difficulties of relating the particular features of general relativity to real physical problems, arises from the high degree of non-linearity of the field equations. Although the linearized theory has been used in some applications, its use is severely limited. Many of the most interesting properties of space-time, such as the occurrence of singularities, are consequences of the non-linearity of the equations. Keywords: General Relativity , Space-Time, Singularities, Non-linearity of the Equations.
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Vasiliev, Valery. "New Solution of a Spherically Symmetric Static Problem of General Relativity." Applied Physics Research 9, no. 5 (August 21, 2017): 29. http://dx.doi.org/10.5539/apr.v9n5p29.
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The paper is concerned with the spherically symmetric static problem of the General Relativity Theory. The classical solution of this problem found in 1916 by K. Schwarzschild for a particular metric form results in singular space metric coefficient and provides the basis of the objects referred to as Black Holes. A more general metric form applied in the paper allows us to obtain the solution which is not singular. The critical radius of the fluid sphere, following from this solution does not coincide with the traditional gravitational radius. For the spheres with radii that are less than the critical value, the solution of GRT problem does not exist.
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BABAK, S. V., and L. P. GRISHCHUK. "FINITE-RANGE GRAVITY AND ITS ROLE IN GRAVITATIONAL WAVES, BLACK HOLES AND COSMOLOGY." International Journal of Modern Physics D 12, no. 10 (December 2003): 1905–59. http://dx.doi.org/10.1142/s0218271803004250.
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Theoretical considerations of fundamental physics, as well as certain cosmological observations, persistently point out to permissibility, and maybe necessity, of macroscopic modifications of the Einstein general relativity. The field theoretical formulation of general relativity helped us to identify the phenomenological seeds of such modifications. They take place in the form of very specific mass terms, which appear in addition to the field theoretical analog of the usual Hilbert–Einstein Lagrangian. We derive and study exact nonlinear equations of the theory, along with its linear approximation. We interpret the added terms as masses of spin-2 and spin-0 gravitons. The arising finite-range gravity is a fully consistent theory, which smoothly approaches general relativity in the massless limit, that is, when both masses tend to zero and the range of gravity tends to infinity. We show that all local weak-field predictions of the theory are in perfect agreement with the available experimental data. However, some other conclusions of the nonlinear massive theory are in a striking contrast with those of general relativity. We show in detail how the arbitrarily small mass terms eliminate the black hole event horizon and replace a permanent power-law expansion of a homogeneous isotropic universe with an oscillatory behaviour. One variant of the theory allows the cosmological scale factor to exhibit an 'accelerated expansion' instead of slowing down to a regular maximum of expansion. We show in detail why the traditional, Fierz–Pauli, massive gravity is in conflict not only with the static-field experiments, but also with the available indirect gravitational-wave observations. At the same time, we demonstrate the incorrectness of the widely held belief that the non-Fierz–Pauli theories possess "negative energies" and "instabilities."
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CAMP, JORDAN, ALEXANDER STROEER, JOHN CANNIZZO, and ROBERT SCHOFIELD. "SEARCHING FOR GRAVITATIONAL WAVES WITH THE HILBERT–HUANG TRANSFORM." Advances in Adaptive Data Analysis 01, no. 04 (October 2009): 643–66. http://dx.doi.org/10.1142/s1793536909000254.
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Gravitational waves are a consequence of Einstein's theory of general relativity applied to the motion of very dense and massive objects such as black holes and neutron stars. Their detection will reveal a wealth of information about these mysterious objects that cannot be obtained with electromagnetic probes. Two projects are underway to attempt the detection of gravitational waves: LISA, a space based mission being designed to search for waves from supermassive black holes at the centers of galaxies, and LIGO, a ground based facility that is now searching for waves from supernovae, pulsars, and the coalescence of black hole and neutron star systems. Because general relativity is an inherently nonlinear theory, many of the predicted source waveforms show strong frequency modulation. In addition, the LIGO and LISA detectors are highly sensitive devices that produce a variety of nonlinear, transient noise features. Thus the unique capabilities of the HHT, the extraction of intrawave modulation and the characterization of nonlinear and nonstationary signals, have a natural application to both signal detection and experimental characterization of the detectors.
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Harko, Tiberiu, and Francisco S. N. Lobo. "Beyond Einstein’s General Relativity: Hybrid metric-Palatini gravity and curvature-matter couplings." International Journal of Modern Physics D 29, no. 13 (September 9, 2020): 2030008. http://dx.doi.org/10.1142/s0218271820300086.
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Einstein’s General Relativity (GR) is possibly one of the greatest intellectual achievements ever conceived by the human mind. In fact, over the last century, GR has proven to be an extremely successful theory, with a well established experimental footing, at least for weak gravitational fields. Its predictions range from the existence of black holes and gravitational radiation (now confirmed) to the cosmological models. Indeed, a central theme in modern Cosmology is the perplexing fact that the Universe is undergoing an accelerating expansion, which represents a new imbalance in the governing gravitational equations. The cause of the late-time cosmic acceleration remains an open and tantalizing question, and has forced theorists and experimentalists to question whether GR is the correct relativistic theory of gravitation. This has spurred much research in modified theories of gravity, where extensions of the Hilbert–Einstein action describe the gravitational field, in particular, [Formula: see text] gravity, where [Formula: see text] is the curvature scalar. In this review, we perform a detailed theoretical and phenomenological analysis of specific modified theories of gravity and investigate their astrophysical and cosmological applications. We present essentially two largely explored extensions of [Formula: see text] gravity, namely: (i) the hybrid metric-Palatini theory; (ii) and modified gravity with curvature-matter couplings. Relative to the former, it has been established that both metric and Palatini versions of [Formula: see text] gravity possess interesting features but also manifest severe drawbacks. A hybrid combination, containing elements from both of these formalisms, turns out to be very successful in accounting for the observed phenomenology and avoids some drawbacks of the original approaches. Relative to the curvature-matter coupling theories, these offer interesting extensions of [Formula: see text] gravity, where the explicit nonminimal couplings between an arbitrary function of the scalar curvature [Formula: see text] and the Lagrangian density of matter, induces a nonvanishing covariant derivative of the energy-momentum tensor, which implies nongeodesic motion and consequently leads to the appearance of an extra force. We extensively explore both theories in a plethora of applications, namely, the weak-field limit, galactic and extragalactic dynamics, cosmology, stellar-type compact objects, irreversible matter creation processes and the quantum cosmology of a specific curvature-matter coupling theory.
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Canazas Garay, Anthonny Freddy. "TEORÍA EFECTIVA PARA ESTRELLAS BINARIAS Y SU APLICACIÓN A ONDAS GRAVITACIONALES." Revista Cientifica TECNIA 25, no. 2 (February 23, 2017): 75. http://dx.doi.org/10.21754/tecnia.v25i2.51.
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Las recientes detecciones de ondas gravitacionales han traído mayor atención al problema de obtener predicciones de alta precisión para los espectros de radiación gravitacional emitidos por sistemas binarios constituidos por agujeros negros o estrellas de neutrones. Este trabajo explica como la teoría de campos efectiva aplicada a la gravitación puede ser usada para describir objetos extendidos interactuando gravitacionalmente como en el caso de un sistema binario. Usando métodos que usualmente se aplican en teoría cuántica de campos se muestra como el sistema binario emite ondas gravitacionales. Palabras clave.- Ondas gravitacionales, Teoría de campos efectiva, Relatividad general, astrofísica, Agujero negro, Estrella de neutrones. ABSTRACTThe recent detections of gravitational waves have brought renewed attention to the problem of obtaining high accuracy predictions for the gravitational radiation spectra emitted by binary systems with black holes or neutron stars constituents. This work explains how effective field theory applied to gravitation can be used to describe a gravitationally interacting extended object as in the binary system case. Gravitational wave emission from the binary system is shown by using methods that are usually applied in quantum field theory. Keywords.- Gravitational waves, Effective field theory, General relativity, Astrophysics, Black hole, Neutron star.
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Will, Clifford M. "Approximation methods in gravitational-radiation theory." Canadian Journal of Physics 64, no. 2 (February 1, 1986): 140–45. http://dx.doi.org/10.1139/p86-023.
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The observation of gravitational-radiation damping in the binary pulsar PSR 1913 + 16 and the ongoing experimental search for gravitational waves of extraterrestrial origin have made the theory of gravitational radiation an active branch of classical general relativity. In calculations of gravitational radiation, approximation methods play a crucial role. We summarize recent developments in two areas in which approximations are important: (a) the quadrupole approximation, which determines the energy flux and the radiation reaction forces in weak-field, slow-motion, source-within-the-near-zone systems such as the binary pulsar; and (b) the normal modes of oscillation of black holes, where the Wentzel–Kramers–Brillouin approximation gives accurate estimates of the complex frequencies of the modes.
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Abedi, Jahed, Niayesh Afshordi, Naritaka Oshita, and Qingwen Wang. "Quantum Black Holes in the Sky." Universe 6, no. 3 (March 10, 2020): 43. http://dx.doi.org/10.3390/universe6030043.
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Black Holes are possibly the most enigmatic objects in our universe. From their detection in gravitational waves upon their mergers, to their snapshot eating at the centres of galaxies, black hole astrophysics has undergone an observational renaissance in the past four years. Nevertheless, they remain active playgrounds for strong gravity and quantum effects, where novel aspects of the elusive theory of quantum gravity may be hard at work. In this review article, we provide an overview of the strong motivations for why “Quantum Black Holes” may be radically different from their classical counterparts in Einstein’s General Relativity. We then discuss the observational signatures of quantum black holes, focusing on gravitational wave echoes as smoking guns for quantum horizons (or exotic compact objects), which have led to significant recent excitement and activity. We review the theoretical underpinning of gravitational wave echoes and critically examine the seemingly contradictory observational claims regarding their (non-)existence. Finally, we discuss the future theoretical and observational landscape for unraveling the “Quantum Black Holes in the Sky”.
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Lo, C. Y. "The Development of Relativity and Einstein." JOURNAL OF ADVANCES IN PHYSICS 10, no. 3 (October 6, 2015): 2874–85. http://dx.doi.org/10.24297/jap.v10i3.1327.
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There are errors in general relativity that must be rectified. As Zhou pointed out, Einstein’s covariance principle is proven to be invalid by explicit examples. Linearization is conditionally valid. Pauli's version of the equivalence principle is impossible in mathematics. Einstein's adaptation of the distance in Riemannian geometry is invalid in physics as pointed out by Whitehead. Moreover, it is inconsistent with the calculation on the bending of light, for which a Euclidean-like framework is necessary. Thus, the interpretation of the Hubble redshifts as due to receding velocities of stars is invalid. The Einstein equation has no dynamic solutions just as Gullstrand suspected. All claims on the existence of dynamic solutions for the Einstein equation are due to mistakes in non-linear mathematics. For the existence of a dynamic solution, the Einstein equation must be modified to the Lorentz-Levy-Einstein equation that have additionally a gravitational energy-stress tensor with an anti-gravity coupling. The existence of photons is a consequence of general relativity. Thus, the space-time singularity theorems of Hawking and Penrose are actually irrelevant to physics because their energy conditions cannot be satisfied. The positive mass theorem of Schoen and Yau is misleading because invalid implicit assumptions are used as Hawking and Penrose did. There are three experiments that show formula E = mc2 is invalid, and a piece of heated-up metal has reduced weight just as a charged capacitor. Thus, the weight is temperature dependent. It is found, due to the repulsive charge-mass interaction, gravity is not always attractive to mass. Since the assumption that gravity is always attractive to mass is not valid, the existence of black holes are questionable. Because of the repulsive charge-mass interaction, the theoretical framework of general relativity must be extended to a five-dimensional relativity of Lo, Goldstein & Napier. Thus Einstein's conjecture of unification is valid. Moreover, the repulsive gravitational force from a charged capacitor is incompatible with the notion of a four-dimensional space. In Quantum theory, currently the charge-mass interaction is neglected. Thus, quantum theory is not a final theory as Einstein claims.
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Zhao, Yaqi, Xin Ren, Amara Ilyas, Emmanuel N. Saridakis, and Yi-Fu Cai. "Quasinormal modes of black holes in f(T) gravity." Journal of Cosmology and Astroparticle Physics 2022, no. 10 (October 1, 2022): 087. http://dx.doi.org/10.1088/1475-7516/2022/10/087.
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Abstract We calculate the quasinormal modes (QNM) frequencies of a test massless scalar field and an electromagnetic field around static black holes in f(T) gravity. Focusing on quadratic f(T) modifications, which is a good approximation for every realistic f(T) theory, we first extract the spherically symmetric solutions using the perturbative method, imposing two ansätze for the metric functions, which suitably quantify the deviation from the Schwarzschild solution. Moreover, we extract the effective potential, and then calculate the QNM frequency of the obtained solutions. Firstly, we numerically solve the Schrödinger-like equation using the discretization method, and we extract the frequency and the time evolution of the dominant mode applying the function fit method. Secondly, we perform a semi-analytical calculation by applying the WKB method with the Pade approximation. We show that the results for f(T) gravity are different compared to General Relativity, and in particular we obtain a different slope and period of the field decay behavior for different model parameter values. Hence, under the light of gravitational-wave observations of increasing accuracy from binary systems, the whole analysis could be used as an additional tool to test General Relativity and examine whether torsional gravitational modifications are possible.
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Yang, Jian Liang. "Light Speed Invariant Solution and Its Enlightenment of Field Equation of General Relativity." Advances in Astronomy 2020 (November 29, 2020): 1–12. http://dx.doi.org/10.1155/2020/3930947.
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A systematic examination of the basic theory of general relativity is made, the meaning of coordinates again is emphasized, the confusion caused by unclear meaning of coordinates in the past is corrected, and the expression of the theory is made more accurate. Firstly, the equation of Einstein’s gravitational field is solved in the usual coordinate system, the existence of light speed invariant solution in the spherically symmetric gravitational field is proved, and in the same time, the solution is determined. It turns out that black holes are not an inevitable prediction of general relativity. The more exact formulas for calculating the curvature of light on the surface of the Sun and the precession angle of the orbit of Mercury are given, and the convergence of general relativistic gravity and special relativistic mechanics under the weak field approximation is realized. Finally, it is shown that the coupling coefficient of the gravitational field equation is not unique. Modifying this coefficient is an ideal project to eliminate the singularities of general relativity on the condition keeping the field equation concise and elegant, and moreover, it reveals that dark matter and dark energy are the negative energy field in the matter, the expansion of the universe is the appearance of the gradual formation of galaxies in accordance with fractal rules, not only the space between galaxies is expanding but also the galaxies themselves are also expanding, new matter is continuously generated in the celestial bodies, for the first time, the unity of fractal geometry and cosmic dynamics of general relativity is realized, and the formation and evolution of galaxies are brought into the fractal generation mode. This is a living and vivacious universe in which all aspects are gradually strengthening, in sharp contrast to the dying universe under the current cosmological framework.
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Haug, Espen Gaarder. "Does Special Relativity Lead to a Trans-Planckian Crisis?" Applied Physics Research 12, no. 1 (December 1, 2019): 1. http://dx.doi.org/10.5539/apr.v12n1p1.
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In gravity theory, there is a well-known trans-Planckian problem, which is that general relativity theory leads
to a shorter than Planck length and shorter than Planck time in relation to so-called black holes. However, there has been little focus on the fact that special relativity also leads to a trans-Planckian problem, something we will demonstrate here. According to special relativity, an object with mass must move slower than light, but special relativity has no limits on how close to the speed of light something with mass can move. This leads to a scenario where objects can undergo so much length contraction that they will become shorter than the Planck length as measured from another frame, and we can also have shorter time intervals than the Planck time.
The trans-Planckian problem is easily solved by a small modification that assumes Haug’s maximum velocity for matter is the ultimate speed limit for something with mass. This speed limit depends on the Planck length, which can be measured without any knowledge of Newton’s gravitational constant or the Planck constant.
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Chou, Yu-Ching, and Weihan Huang. "A novel singularity-free black hole with nonlinear magnetic monopole: Hawking radiation and quantum correction." Papers in Physics 14 (April 12, 2022): 140006. http://dx.doi.org/10.4279/pip.140006.
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This paper introduces a nonlinear, magnetically charged, singularity-free black hole model. The Ricci scalar, Kretschmann scalar, horizon, energy conditions, and Hawking radiation corresponding to the singularity-free metric are presented, and the asymptotic behavior and quantum correction of the model are examined. The model was constructed by coupling a mass function with the regular black hole solution under nonlinear electrodynamics in general relativity. Aside from resolving the problem of singularities in Einstein’s theory of general relativity, the model asymptotically meets the quantum correction under an effective field theory. This obviates the need for additional correction terms; in this regard, the model outperforms the black hole models developed by Bardeen and Hayward. Regarding the nonlinear magnetic monopole source of the gravitational field of the black hole, the energy–momentum tensors fulfill weak energy conditions. The model constitutes a novel, spherically symmetric solution to regular black holes.
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Gair, Jonathan R. "The black hole symphony: probing new physics using gravitational waves." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 366, no. 1884 (September 23, 2008): 4365–79. http://dx.doi.org/10.1098/rsta.2008.0170.
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The next decade will very likely see the birth of a new field of astronomy as we become able to directly detect gravitational waves (GWs) for the first time. The existence of GWs is one of the key predictions of Einstein's theory of general relativity, but they have eluded direct detection for the last century. This will change thanks to a new generation of laser interferometers that are already in operation or which are planned for the near future. GW observations will allow us to probe some of the most exotic and energetic events in the Universe, the mergers of black holes. We will obtain information about the systems to a precision unprecedented in astronomy, and this will revolutionize our understanding of compact astrophysical systems. Moreover, if any of the assumptions of relativity theory are incorrect, this will lead to subtle, but potentially detectable, differences in the emitted GWs. Our observations will thus provide very precise verifications of the theory in an as yet untested regime. In this paper, I will discuss what GW observations could tell us about known and (potentially) unknown physics.
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Younsi, Ziri, Dimitrios Psaltis, and Feryal Özel. "Black Hole Images as Tests of General Relativity: Effects of Spacetime Geometry." Astrophysical Journal 942, no. 1 (January 1, 2023): 47. http://dx.doi.org/10.3847/1538-4357/aca58a.
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Abstract The images of supermassive black holes surrounded by optically thin, radiatively inefficient accretion flows, like those observed with the Event Horizon Telescope, are characterized by a bright ring of emission surrounding the black hole shadow. In the Kerr spacetime, this bright ring, when narrow, closely traces the boundary of the shadow and can, with appropriate calibration, serve as its proxy. The present paper expands the validity of this statement by considering two particular spacetime geometries: a solution to the field equations of a modified gravity theory and another that parametrically deviates from Kerr but recovers the Kerr spacetime when its deviation parameters vanish. A covariant, axisymmetric analytic model of the accretion flow based on conservation laws and spanning a broad range of plasma conditions is utilized to calculate synthetic non-Kerr black hole images, which are then analyzed and characterized. We find that in all spacetimes: (i) it is the gravitationally lensed unstable photon orbit that plays the critical role in establishing the diameter of the rings observed in black hole images, not the event horizon or the innermost stable circular orbit, (ii) bright rings in these images scale in size with, and encompass, the boundaries of the black hole shadows, even when deviating significantly from Kerr, and (iii) uncertainties in the physical properties of the accreting plasma introduce subdominant corrections to the relation between the diameter of the image and the diameter of the black hole shadow. These results provide important new theoretical justification for using black hole images to probe and test the spacetimes of supermassive black holes.
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Et. al., Dr Indrajit Patra,. "Do They Compute? Dawn of a New Paradigm based on the Information-theoretic View of Black holes, Universe and Various Conceptual Interconnections of Fundamental Physics." Turkish Journal of Computer and Mathematics Education (TURCOMAT) 12, no. 2 (April 11, 2021): 1208–21. http://dx.doi.org/10.17762/turcomat.v12i2.1145.
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The article endeavors to show how thinking about black holes as some form of hyper-efficient, serial computers could help us in thinking about the more fundamental aspects of space-time itself. Black holes as the most exotic and yet simplest forms of gravitational systems also embody quantum fluctuations that could be manipulated to archive hypercomputation, and even if this approach might not be realistic, yet it is important since it has deep connections with various aspects of quantum gravity, the highly desired unification of quantum mechanics and general relativity. The article describes how thinking about black holes as the most efficient kind of computers in the physical universe also paves the way for developing new ideas about such issues as black hole information paradox, the possibility of emulating the properties of curved space-time with the collective quantum behaviors of certain kind of condensate fluids, ideas of holographic spacetime, gravitational thermodynamics and entropic gravity, the role of quantum entanglements and non-locality in the construction of spacetime, spacetime geometry and the nature of gravitation and dark energy and dark matter, etc. to name a few.
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SI, Konstantinov. "Quantum Theory of Gravity and Arthur Eddingtons Fundamental Theory." Journal of Biomedical Research & Environmental Sciences 2, no. 11 (December 2021): 1092–100. http://dx.doi.org/10.37871/jbres1353.
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For the first time, the article presents the Quantum Theory of Gravity, covering not only the microcosm of elementary particles, but also the macrocosm of planets, stars and black holes. This relational approach to gravity was consistently presented in Arthur Eddington's monograph “Fundamental Theory”. In the theory of quantum gravity proposes to consider instead of gravity holes in the curved space-time of Einstein's general relativity, gravitational funnels formed by the rotation of planets, stars and galaxies in a dark matter halo. The change in the gravitational potential in the funnels occurs instantly in all areas of the gravitational funnel space in accordance with the pressure gradient described by the Euler-Bernoulli equation for superfluid continuous media. The new cosmological theory represents the evolution of the universe and dark holes without a singularity. The disordered alternation of the processes of contraction and expansion of individual regions of the infinite Universe realizes the circulation of baryonic and dark matter, which allows it to exist indefinitely, bypassing the state of equilibrium. Numerical modeling allows us to assert that the theory of quantum gravity is the most reliable of the three generally accepted theories of gravity.
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Nakonieczna, Anna, Łukasz Nakonieczny, and Dong-Han Yeom. "Black hole factory: A review of double-null formalism." International Journal of Modern Physics D 28, no. 03 (February 2019): 1930006. http://dx.doi.org/10.1142/s0218271819300064.
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In this review paper, we comprehensively summarize numerical applications of double-null formalism for studying dynamics within the theory of gravity. By using the double-null coordinates, we can investigate dynamical black holes and gravitational phenomena within spherical symmetry, including gravitational collapse, formation of horizons and singularities, as well as evaporations. This formalism can be extended to generic situations, where we can change dimensions, topologies, the gravity sector, as well as the matter sector. We also discuss its possible implications for black hole physics and particle astrophysics. This strong numerical tool will have lots of future applications for various research areas including general relativity, string theory and various approaches to quantum gravity.
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HSU, STEPHEN D. H., and DAVID REEB. "MONSTERS, BLACK HOLES AND THE STATISTICAL MECHANICS OF GRAVITY." Modern Physics Letters A 24, no. 24 (August 10, 2009): 1875–87. http://dx.doi.org/10.1142/s0217732309031624.
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We review the construction of monsters in classical general relativity. Monsters have finite ADM mass and surface area, but potentially unbounded entropy. From the curved space perspective, they are objects with large proper volume that can be glued on to an asymptotically flat space. At no point is the curvature or energy density required to be large in Planck units, and quantum gravitational effects are, in the conventional effective field theory framework, small everywhere. Since they can have more entropy than a black hole of equal mass, monsters are problematic for certain interpretations of black hole entropy and the AdS/CFT duality. In the second part of the paper we review recent developments in the foundations of statistical mechanics which make use of properties of high-dimensional (Hilbert) spaces. These results primarily depend on kinematics — essentially, the geometry of Hilbert space — and are relatively insensitive to dynamics. We discuss how this approach might be adopted as a basis for the statistical mechanics of gravity. Interestingly, monsters and other highly entropic configurations play an important role.
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Adhikary, Subhrangshu, and Saikat Banerjee. "Binary Black Hole Automated Identification by Agglomerative Clustering based on Gravitational Waves." Journal of Physics: Conference Series 2089, no. 1 (November 1, 2021): 012027. http://dx.doi.org/10.1088/1742-6596/2089/1/012027.
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Abstract The General Theory of Relativity, proposed by Albert Einstein theoretically predicted that very large accelerating mass creates ripples in spacetime which is the strongest for merging binary black hole system and the ripples can travel billions of light-years and these ripples are called Gravitational Waves. By the time these waves reach Earth, they become very faint and can’t be detected with regular methods. For this, LIGO has created specialized detectors based on the laser interference principle to detect strains caused by gravitational waves in e-19 scale. GW190521 is a gravitational wave event recorded on 21 May 2019 at 03:02:29 UTC and caused by the merger of two black holes of 85M© and 66 M© whose progenitor was the largest ever recorded. Throughout literature, very few amounts of autonomous black hole identification models have been made because of limited data availability. This experiment proposes methods for autonomous identification of black holes by using an unsupervised machine learning algorithm called Agglomerative Clustering with very little data to train which can adapt quickly to gravitational wave events. The model could be easily deployed near laser interferometric observatories for autonomous black hole identification with minimal effort.
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Calmet, Xavier. "The lightest of black holes." Modern Physics Letters A 29, no. 38 (December 9, 2014): 1450204. http://dx.doi.org/10.1142/s0217732314502046.
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In this paper, we consider general relativity in the large N limit, where N stands for the number of particles in the model. Studying the resummed graviton propagator in the linearized regime, we propose to interpret its complex poles as black hole precursors. Our main result is the calculation of the mass and width of the lightest of black holes. We show that the values of the masses of black hole precursors depend on the number of fields in the theory. Their masses can be lowered down to the TeV region by increasing the number of fields in a hidden sector that only interacts gravitationally with the Standard Model.
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JOSHI, PANKAJ S., and DANIELE MALAFARINA. "RECENT DEVELOPMENTS IN GRAVITATIONAL COLLAPSE AND SPACETIME SINGULARITIES." International Journal of Modern Physics D 20, no. 14 (December 31, 2011): 2641–729. http://dx.doi.org/10.1142/s0218271811020792.
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It is now known that when a massive star collapses under the force of its own gravity, the final fate of such a continual gravitational collapse will be either a black hole or a naked singularity under a wide variety of physically reasonable circumstances within the framework of general theory of relativity. The research of recent years has provided considerable clarity and insight on stellar collapse, black holes and the nature and structure of spacetime singularities. We discuss several of these developments here. There are also important fundamental questions that remain unanswered on the final fate of collapse of a massive matter cloud in gravitation theory, especially on naked singularities which are hypothetical astrophysical objects and on the nature of cosmic censorship hypothesis. These issues have key implications for our understanding on black hole physics today, its astrophysical applications, and for certain basic questions in cosmology and possible quantum theories of gravity. We consider these issues here and summarize recent results and current progress in these directions. The emerging astrophysical and observational perspectives and implications are discussed, with particular reference to the properties of accretion disks around black holes and naked singularities, which may provide characteristic signatures and could help distinguish these objects.
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Mustari, Mustari, and Yuant Tiandho. "Thermodynamics of a Non-Stationary Black Hole Based on Generalized Uncertainty Principle." Journal of Physics: Theories and Applications 1, no. 2 (October 29, 2017): 127. http://dx.doi.org/10.20961/jphystheor-appl.v1i2.19308.
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In the general theory of relativity (GTR), black holes are defined as objects with very strong gravitational fields even light can not escape. Therefore, according to GTR black hole can be viewed as a non-thermodynamic object. The worldview of a black hole began to change since Hawking involves quantum field theory to study black holes and found that black holes have temperatures that analogous to black body radiation. In the theory of quantum gravity there is a term of the minimum length of an object known as the Planck length that demands a revision of Heisenberg's uncertainty principle into a Generalized Uncertainty Principle (GUP). Based on the relationship between the momentum uncertainty and the characteristic energy of the photons emitted by a black hole, the temperature and entropy of the non-stationary black hole (Vaidya-Bonner black hole) were calculated. The non-stationary black hole was chosen because it more realistic than static black holes to describe radiation phenomena. Because the black hole is dynamic then thermodynamics studies are conducted on both black hole horizons: the apparent horizon and its event horizon. The results showed that the dominant correction term of the temperature and entropy of the Vaidya-Bonner black hole are logarithmic.
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Saravani, Mehdi, Niayesh Afshordi, and Robert B. Mann. "Empty black holes, firewalls, and the origin of Bekenstein–Hawking entropy." International Journal of Modern Physics D 23, no. 13 (November 2014): 1443007. http://dx.doi.org/10.1142/s021827181443007x.
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We propose a novel solution for the endpoint of gravitational collapse, in which spacetime ends (and is orbifolded) at a microscopic distance from black hole event horizons. This model is motivated by the emergence of singular event horizons in the gravitational aether theory, a semiclassical solution to the cosmological constant problem(s) and thus suggests a catastrophic breakdown of general relativity close to black hole event horizons. A similar picture emerges in fuzzball models of black holes in string theory, as well as the recent firewall proposal to resolve the information paradox. We then demonstrate that positing a surface fluid in thermal equilibrium with Hawking radiation, with vanishing energy density (but nonvanishing pressure) at the new boundary of spacetime, which is required by Israel junction conditions, yields a thermodynamic entropy that is identical to the Bekenstein–Hawking area law, SBH, for charged rotating black holes. To our knowledge, this is the first derivation of black hole entropy that only employs local thermodynamics. Furthermore, a model for the microscopic degrees of freedom of the surface fluid (which constitute the microstates of the black hole) is suggested, which has a finite, but Lorentz-violating, quantum field theory. Finally, we comment on the effects of physical boundary on Hawking radiation and show that relaxing the assumption of equilibrium with Hawking radiation sets SBH as an upper limit for Black Hole entropy.
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BERTI, EMANUELE, and VITOR CARDOSO. "SUPERMASSIVE BLACK HOLES OR BOSON STARS? HAIR COUNTING WITH GRAVITATIONAL WAVE DETECTORS." International Journal of Modern Physics D 15, no. 12 (December 2006): 2209–16. http://dx.doi.org/10.1142/s0218271806009637.
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The evidence for supermassive Kerr black holes in galactic centers is strong and growing, but only the detection of gravitational waves will convincingly rule out other possibilities to explain the observations. The Kerr space–time is completely specified by the first two multipole moments: mass and angular momentum. This is usually referred to as the "no-hair theorem," but it is really a "two-hair" theorem. If general relativity is the correct theory of gravity, the most plausible alternative to a supermassive Kerr black hole is a rotating boson star. Numerical calculations indicate that the space–time of rotating boson stars is determined by the first three multipole moments ("three-hair theorem"). The Laser Interferometer Space Antenna (LISA) could accurately measure the oscillation frequencies of these supermassive objects. We propose to use these measurements to "count their hair," unambiguously determining their nature and properties.
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Xavier, Sérgio Vinicius Monteiro C. B., Pedro V. P. Cunha, Luís C. B. Crispino, and Carlos A. R. Herdeiro. "Shadows of charged rotating black holes: Kerr–Newman versus Kerr–Sen." International Journal of Modern Physics D 29, no. 11 (August 2020): 2041005. http://dx.doi.org/10.1142/s0218271820410059.
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Celebrating the centennial of its first experimental test, the theory of General Relativity (GR) has successfully and consistently passed all subsequent tests with flying colors. It is expected, however, that at certain scales new physics, in particular, in the form of quantum corrections, will emerge, changing some of the predictions of GR, which is a classical theory. In this respect, black holes (BHs) are natural configurations to explore the quantum effects on strong gravitational fields. BH solutions in the low-energy effective field theory description of the heterotic string theory, which is one of the leading candidates to describe quantum gravity, have been the focus of many studies in the last three decades. The recent interest in strong gravitational lensing by BHs, in the wake of the Event Horizon Telescope (EHT) observations, suggests comparing the BH lensing in both GR and heterotic string theory, in order to assess the phenomenological differences between these models. In this work, we investigate the differences in the shadows of two charged BH solutions with rotation: one arising in the context of GR, namely the Kerr–Newman (KN) solution, and the other within the context of low-energy heterotic string theory, the Kerr–Sen (KS) solution. We show and interpret, in particular, that the stringy BH always has a larger shadow, for the same physical parameters and observation conditions.
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NIEUWENHUIZEN, THEO M. "EXACT SOLUTION FOR THE INTERIOR OF A BLACK HOLE." Fluctuation and Noise Letters 08, no. 02 (June 2008): L141—L153. http://dx.doi.org/10.1142/s0219477508004441.
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Within the Relativistic Theory of Gravitation it is shown that the equation of state p = ρ holds near the center of a black hole. For the stiff equation of state p = ρ − ρc the interior metric is solved exactly. It is matched with the Schwarzschild metric, which is deformed in a narrow range beyond the horizon. The solution is regular everywhere, with a specific shape at the origin. The gravitational redshift at the horizon remains finite but is large, z ~ 1023 M⊙/M. Time keeps its standard role also in the interior. The energy of the Schwarzschild metric, shown to be minus infinity in the General Theory of Relativity, is regularized in this setup, resulting in E = Mc2.
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Manchester, R. N. "Pulsars and gravity." International Journal of Modern Physics D 24, no. 06 (April 27, 2015): 1530018. http://dx.doi.org/10.1142/s0218271815300189.
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Pulsars are wonderful gravitational probes. Their tiny size and stellar mass give their rotation periods a stability comparable to that of atomic frequency standards. This is especially true of the rapidly rotating "millisecond pulsars" (MSPs). Many of these rapidly rotating pulsars are in orbit with another star, allowing pulsar timing to probe relativistic perturbations to the orbital motion. Pulsars have provided the most stringent tests of theories of relativistic gravitation, especially in the strong-field regime, and have shown that Einstein's general theory of relativity is an accurate description of the observed motions. Many other gravitational theories are effectively ruled out or at least severely constrained by these results. MSPs can also be used to form a "Pulsar Timing Array" (PTA). PTAs are Galactic-scale interferometers that have the potential to directly detect nanohertz gravitational waves from astrophysical sources. Orbiting super-massive black holes in the cores of distant galaxies are the sources most likely to be detectable. Although no evidence for gravitational waves has yet been found in PTA data sets, the latest limits are seriously constraining current ideas on galaxy and black-hole evolution in the early universe.
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Papanikolaou, Theodoros, Charalampos Tzerefos, Spyros Basilakos, and Emmanuel N. Saridakis. "Scalar induced gravitational waves from primordial black hole Poisson fluctuations in f(R) gravity." Journal of Cosmology and Astroparticle Physics 2022, no. 10 (October 1, 2022): 013. http://dx.doi.org/10.1088/1475-7516/2022/10/013.
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Abstract The gravitational potential of a gas of initially randomly distributed primordial black holes (PBH) can induce a stochastic gravitational-wave (GW) background through second-order gravitational effects. This GW background can be abundantly generated in a cosmic era dominated by ultralight primordial black holes, with masses m PBH < 109g. In this work, we consider f(R) gravity as the underlying gravitational theory and we study its effect at the level of the gravitational potential of Poisson distributed primordial black holes. After a general analysis, we focus on the R 2 gravity model. In particular, by requiring that the scalar induced GWs (SIGWs) are not overproduced, we find an upper bound on the abundance of PBHs at formation time ΩPBH,f as a function of their mass, namely that ΩPBH,f < 5.5 × 10-5 (109g/m PBH)1/4, which is 45% tighter than the respective upper bound in general relativity. Afterwards, by considering R 2 gravity as an illustrative case study of an f(R) gravity model, we also set upper bound constraints on its mass parameter M. These mass parameter constraints, however, should not be regarded as physical given the fact that the Cosmic Microwave Background (CMB) constraints on R 2 gravity are quite tight. Finally, we conclude that the portal of SIGWs associated to PBH Poisson fluctuations can act as a novel complementary probe to constrain alternative gravity theories.
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Jinzhong, Liu, and Zhang Yu. "A binary population synthesis study on gravitational wave sources." Proceedings of the International Astronomical Union 11, A29B (August 2015): 365–66. http://dx.doi.org/10.1017/s1743921316005548.
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AbstractGravitational waves (GW) are a natural consequence of Einstein's theory of gravity (general relativity), and minute distortions of space-time. Gravitational Wave Astronomy is an emerging branch of observational astronomy which aims to use GWs to collect observational data about objects such as neutron stars and black holes, about events such as supernovae and about the early universe shortly after the big bang.This field will evolve to become an established component of 21st century multi-messenger astronomy, and will stand shoulder-to-shoulder with gamma-ray, x-ray, optical, infrared and radio astronomers in exploring the cosmos. In this paper, we state a recent theoretical study on GW sources, and present the results of our studies on the field using a binary population synthesis (BPS) approach, which was designed to investigate the formation of many interesting binary-related objects, including close double white dwarfs, AM CVn stars, ultra-compact X-ray binaries(UCXBs), double neutron stars, double stellar black holes. Here we report how BPS can be used to determine the GW radiation from double compact objects.
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Nashed, G. G. L., and Shin'ichi Nojiri. "Black holes with Lagrange multiplier and potential in mimetic-like gravitational theory: multi-horizon black holes." Journal of Cosmology and Astroparticle Physics 2022, no. 05 (May 1, 2022): 011. http://dx.doi.org/10.1088/1475-7516/2022/05/011.
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Abstract In this paper, we consider the mimetic-like field equations coupled with the Lagrange multiplier and the potential to derive non-trivial spherically symmetric black hole (BH) solutions. We divided this study into three cases: in the first one, we choose the Lagrange multiplier and the potential to vanish and derive a BH solution that coincides with the BH of the Einstein general relativity despite the non-vanishing value of the mimetic-like scalar field. The first case is consistent with the previous studies in the literature where the mimetic theory coincides with GR [1]. In the second case, we derive a solution with a constant value of the potential and a dynamical value of the Lagrange multiplier. This solution has no horizon, and therefore, the obtained space-time does not correspond to the BH. In this solution, there appears a region of the Euclidian signature where the signature of the diagonal components of the metric is (+,+,+,+) or the region with two times where the signature is (+,+,-,-). Finally, we derive a BH solution with non-vanishing values of the Lagrange multiplier, potential, and mimetic-like scalar field. This BH shows a soft singularity compared with the Einstein BH solution. The relevant physics of the third case is discussed by showing their behavior of the metric potential at infinity, calculating their energy conditions, and studying their thermodynamical quantities. We give a brief discussion on how our third case can generate a BH with three horizons as in the de Sitter-Reissner-Nordström black hole space-time, where the largest horizon is the cosmological one and two correspond to the outer and inner horizons of the BH. Even in the third case, the region of the Euclidian signature or the region with two times appears. We give a condition that such unphysical region(s) is hidden inside the black hole horizon and the existence of the region(s) becomes less unphysical. We also study the thermodynamics of the multi-horizon BH and consider the extremal case, where the radii of two horizons coincide with each other. We observe that the Hawking temperature and the heat capacity vanish in the extremal limit. Finally, we would like to stress the fact that in spite that the field equations we use have no cosmological constant, our BH solutions of the second and third case behave asymptotically as AdS/dS.
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Gorbatenko, M. V., and V. P. Neznamov. "Quantum mechanics of stationary states of particles in external singular spherically and axially symmetric gravitational and electromagnetic fields." International Journal of Modern Physics A 35, no. 02n03 (January 24, 2020): 2040013. http://dx.doi.org/10.1142/s0217751x20400138.
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The report considers the interaction of scalar particles, photons and fermions with the gravitational and electromagnetic Schwarzschild, Reissner-Nordström, Kerr and Kerr-Newman fields. The behavior of effective potentials in the relativistic Schrödinger-type second-order equations is analyzed. It was found that the quantum theory is incompatible with the hypothesis of the existence of classical black holes with event horizons of zero thickness that were predicted based on solutions of the general relativity (GR) with zero and non-zero cosmological constant [Formula: see text]. The alternative may be presented by compound systems, i.e., collapsars with fermions in stationary bound states.
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De, Shounak, Tejinder P. Singh, and Abhinav Varma. "Quantum gravity as an emergent phenomenon." International Journal of Modern Physics D 28, no. 14 (October 2019): 1944003. http://dx.doi.org/10.1142/s0218271819440036.
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There ought to exist a reformulation of quantum theory which does not depend on classical time. To achieve such a reformulation, we introduce the concept of an atom of space-time-matter (STM). An STM atom is a classical noncommutative geometry (NCG), based on an asymmetric metric, and sourced by a closed string. Different such atoms interact via entanglement. The statistical thermodynamics of a large number of such atoms gives rise, at equilibrium, to a theory of quantum gravity. Far from equilibrium, where statistical fluctuations are large, the emergent theory reduces to classical general relativity. In this theory, classical black holes are far from equilibrium low entropy states, and their Hawking evaporation represents an attempt to return to the [maximum entropy] equilibrium quantum gravitational state.
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Pfeifer, Christian, and Sebastian Schuster. "Static Spherically Symmetric Black Holes in Weak f(T)-Gravity." Universe 7, no. 5 (May 17, 2021): 153. http://dx.doi.org/10.3390/universe7050153.
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With the advent of gravitational wave astronomy and first pictures of the “shadow” of the central black hole of our milky way, theoretical analyses of black holes (and compact objects mimicking them sufficiently closely) have become more important than ever. The near future promises more and more detailed information about the observable black holes and black hole candidates. This information could lead to important advances on constraints on or evidence for modifications of general relativity. More precisely, we are studying the influence of weak teleparallel perturbations on general relativistic vacuum spacetime geometries in spherical symmetry. We find the most general family of spherically symmetric, static vacuum solutions of the theory, which are candidates for describing teleparallel black holes which emerge as perturbations to the Schwarzschild black hole. We compare our findings to results on black hole or static, spherically symmetric solutions in teleparallel gravity discussed in the literature, by comparing the predictions for classical observables such as the photon sphere, the perihelion shift, the light deflection, and the Shapiro delay. On the basis of these observables, we demonstrate that among the solutions we found, there exist spacetime geometries that lead to much weaker bounds on teleparallel gravity than those found earlier. Finally, we move on to a discussion of how the teleparallel perturbations influence the Hawking evaporation in these spacetimes.
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Toscani, Martina, Giuseppe Lodato, Daniel J. Price, and David Liptai. "Gravitational waves from tidal disruption events: an open and comprehensive catalog." Monthly Notices of the Royal Astronomical Society 510, no. 1 (December 3, 2021): 992–1001. http://dx.doi.org/10.1093/mnras/stab3384.
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ABSTRACT We present an online, open, and comprehensive template library of gravitational waveforms produced during the tidal disruptions of stars by massive black holes, spanning a broad space of parameters. We build this library thanks to a new feature that we implement in the general relativistic version of phantom, a smoothed particle hydrodynamics code for three dimensional simulations in general relativity. We first perform a series of numerical tests to show that the gravitational wave (GW) signal obtained is in excellent agreement with the one expected from theory. This benchmark is done for well studied scenarios (such as binary stellar systems). We then apply our code to calculate the GW signals from tidal disruption events, finding that our results are consistent with the theoretical estimates obtained in previous studies for selected parameters. We illustrate interesting results from the catalog, where we stress how the gravitational signal is affected by variations of some parameters (like black hole spin, stellar orbital eccentricity, and inclination). The full catalog is available online. It is intended to be a living catalog.