Topic
Gravitation
About: Gravitation is a research topic. Over the lifetime, 29306 publications have been published within this topic receiving 821510 citations.
Papers published on a yearly basis
Papers
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TL;DR: In this article, an exact lens equation without reference to a background spacetime is given for the case of Schwarzschild spacetime, where the light rays are geodesics of the background with sharp bending in the lens plane.
Abstract: (November 29, 1999)We propose a definition of an exact lens equation without reference to a background spacetime,and construct the exact lens equation explicitly in the case of Schwarzschild spacetime For theSchwarzschild case, we give exact expressions for the angular-diameter distance to the sources aswell as for the magnification factor and time of arrival of the images We compare the exactlens equation with the standard lens equation, derived under the thin-lens-weak-field assumption(where the light rays are geodesics of the background with sharp bending in the lens plane, andthe gravitational field is weak), and verify the fact that the standard weak-field thin-lens equationis inadequate at small impact parameter We show that the second-order correction to the weak-field thin-lens equation is inaccurate as well Finally, we compare the exact lens equation with therecently proposed strong-field thin-lens equation, obtained under the assumption of straight pathsbut without the small angle approximation, ie, with allowed large bending angles We show thatthe strong-field thin-lens equation is remarkably accurate, even for lightrays that take several turnsaround the lens before reaching the observerI INTRODUCTION
215 citations
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215 citations
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TL;DR: In this article, it was shown that the Schwarzschild-de-Sitter solution is not the unique spherically-symmetric vacuum solution, and therefore not the solution that describes the spacetime in the solar system.
Abstract: Shortly after the addition of a 1/R term to the Einstein-Hilbert action was proposed as a solution to the cosmic-acceleration puzzle, Chiba showed that such a theory violates Solar System tests of gravity. A flurry of recent papers have called Chiba's result into question. They argue that the spherically-symmetric vacuum spacetime in this theory is the Schwarzschild-de Sitter solution, making this theory consistent with Solar System tests. We point out that although the Schwarzschild-de Sitter solution exists in this theory, it is not the unique spherically-symmetric vacuum solution, and it is not the solution that describes the spacetime in the Solar System. The solution that correctly matches onto the stellar-interior solution differs from Schwarzschild-de Sitter in a way consistent with Chiba's claims. Thus, 1/R gravity is ruled out by Solar System tests.
215 citations
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26 Oct 1989TL;DR: In this article, a detailed review of research into gravitational collapse, and several examples of collapse models are investigated in detail, including how the visible ultra-dense regions arise naturally and generically as an outcome of dynamical gravitational collapse.
Abstract: Physical phenomena in astrophysics and cosmology involve gravitational collapse in a fundamental way. The final fate of a massive star when it collapses under its own gravity at the end of its life cycle is one of the most important questions in gravitation theory and relativistic astrophysics, and is the foundation of black hole physics. General relativity predicts that continual gravitational collapse gives rise to a space-time singularity. Quantum gravity may take over in such regimes to resolve the classical space-time singularity. This book investigates these issues, and shows how the visible ultra-dense regions arise naturally and generically as an outcome of dynamical gravitational collapse. It will be of interest to graduate students and academic researchers in gravitation physics, fundamental physics, astrophysics, and cosmology. It includes a detailed review of research into gravitational collapse, and several examples of collapse models are investigated in detail.
215 citations
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01 Jul 2020TL;DR: In this article, a five-dimensional asymptotically AdS geometry whose boundary realizes a four-dimensional Hartle-Hawking state on an eternal AdS black hole in equilibrium with a bath was constructed.
Abstract: It has been suggested in recent work that the Page curve of Hawking radiation can be recovered using computations in semi-classical gravity provided one allows for "islands" in the gravity region of quantum systems coupled to gravity. The explicit computations so far have been restricted to black holes in two-dimensional Jackiw-Teitelboim gravity. In this note, we numerically construct a five-dimensional asymptotically AdS geometry whose boundary realizes a four-dimensional Hartle-Hawking state on an eternal AdS black hole in equilibrium with a bath. We also numerically find two types of extremal surfaces: ones that correspond to having or not having an island. The version of the information paradox involving the eternal black hole exists in this setup, and it is avoided by the presence of islands. Thus, recent computations exhibiting islands in two-dimensional gravity generalize to higher dimensions as well.
215 citations