Gravitational collapse: an overview (original) (raw)

Simple analytical models of gravitational collapse

American Journal of Physics, 2005

Most general relativity textbooks devote considerable space to the simplest example of a black hole containing a singularity, the Schwarzschild geometry. However only a few discuss the dynamical process of gravitational collapse, by which black holes and singularities form. We present here two types of analytic models for this process, which we believe are the simplest available; the first involves collapsing spherical shells of light, analyzed mainly in Eddington-Finkelstein coordinates; the second involves collapsing spheres filled with a perfect fluid, analyzed mainly in Painleve-Gullstrand coordinates. Our main goal is pedagogical simplicity and algebraic completeness, but we also present some results that we believe are new, such as the collapse of a light shell in Kruskal-Szekeres coordinates.

RECENT DEVELOPMENTS IN GRAVITATIONAL COLLAPSE AND SPACETIME SINGULARITIES

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.

On continued gravitational collapse

2000

According to a widespread idee fixe, the spherically-symmetric collapse of a sufficiently massive celestial body of spherical shape should generate a black hole. I prove that this process generates simply an ordinary point mass. My argument is model-independent.

Collapsing gravity models considered critically

We reinvestigate the classical collapsing models of Oppenheimer-Snyder and McVittie and Weinberg. Although these models have been well known for decades and widely quoted, it is worth to studying them more thoroughly.

Revisiting the semiclassical gravity scenario for gravitational collapse

AIP Conference Proceedings, 2009

The existence of extremely dark and compact astronomical bodies is by now a well established observational fact. On the other hand, classical General Relativity predicts the existence of black holes which fit very well with the observations, but do lead to important conceptual problems. In this contribution we ask ourselves the straightforward question: Are the dark and compact objects that we have observational evidence for black holes in the sense of General Relativity? By revising the semiclassical scenario of stellar collapse we find out that as the result of a collapse some alternative objects could be formed which might supplant black holes.

Stellar Collapse in Field Theories of Gravitation

2010

Collapse in general relativity encounters contradictions unless the Einstein-Hilbert theory is reformulated as a …eld theory on a space metric that is homogeneous and isotropic at large distance (Minkowski space-time). The classic 'black hole'solution of Oppenheimer and Snyder fails to satisfy a matching condition at the surface of a collapsing 'dust'ball. Correcting this error leads to a new solution in which the contraction process stops at the Schwarzschild radius and particles accumulate at the surface of the ball. Catastrophic collapse into a black hole is prevented by the increasing gravitational energy inside the ball, which results in gravity changing from attractive to repulsive. The result con…rms Einstein's and Eddington's judgements about gravitational collapse; the process, throughout the ball, comes to a halt as the escape velocity at the surface approaches that of light.

On the Relativistic Gravitational Collapse et Cetera

Istituto Lombardo - Accademia di Scienze e Lettere - Rendiconti di Scienze, 2014

ON THE RELATIVISTIC GRAVITATIONAL COLLAPSE ET CETERA Nota del m.e. ANGELO LOINGER (*) e di TIZIANA MARSICO (**) (Adunanza del 23 ottobre 2014) SUNTO.-Sfere di "polvere" di grande massa collassano gravitazionalmente in "sfere piene" compatte di volumi finiti, le cui superfici hanno le medesime proprietà dell'orizzonte degli eventi associato alla gravitazione di un punto materiale. Sia l'orizzonte degli eventi di una "sfera piena" sia quello associato ad un punto materiale, in virtù della repulsione gravitazionale hilbertiana non possono "inghiottire" alcunché, contrariamente a quanto afferma un locus communis. I dati osservazionali convalidano i nostri risultati. *** 1.-The main theme of this paper is treated in sect. 5. In sect. 2 we recall a general expression (de Sitter, Eddington, Levi-Civita) of the

Gravitational Collapse and Black Holes

2019

We discuss how Schwarzschild coordinates behave at the horizon and point out that Schwarzschild coordinates do not describe the geometry at horizon properly and, therefore, we need another coordinate system which is called "The Kruskal-Szekeres coordinates". Nature of horizons are also analysed. We prove that Schwarzschild metric is the unique solution to the vacuum with spherical symmetry, i.e. Birkhoof's Theorem. Conserved quantities of black holes and No-Hair Theorem are mentiones shortly and it's also discussed that how black holes can be used to produce energy more efficiently compared to other sources.

New mathematical framework for spherical gravitational collapse

Classical and Quantum Gravity, 2003

A theorem, giving necessary and sufficient condition for naked singularity formation in spherically symmetric non static spacetimes under hypotheses of physical acceptability, is formulated and proved. The theorem relates existence of singular null geodesics to existence of regular curves which are super-solutions of the radial null geodesic equation, and allows us to treat all the known examples of naked singularities from a unified viewpoint. New examples are also found using this approach, and perspectives are discussed.

Globally Causal Solutions for Gravitational Collapse

Through an illuminating thought experiment we demonstrate that the nonsingular "continued collapse" picture of a black hole is the only consistent and physical one. We provide a class exact solutions on the boundary of the space of physical configurations. This will show that all the other known exact solutions are unphysical near the surface of the event horizon or in the interior. This will have important consequences for the "no-hair" conjecture and the kinds of persistent fields that can emerge from a black hole as well as the evolution during collisions and near grazing events. The interior of these holes are characterized by a limiting degenerate metric and these regions tend to well defined volumes and radii in contrast with what is inferred from singular solutions. Surprisingly, these depend on past history and not simply the mass or external fields of the body. It is shown that there is often a well defined "hidden" flat background that can be used to equivalently reformulate GR in terms of a classical nonlinear gravity field and gives local conservation laws. This has implications for unification efforts and numerical approaches to handle the degenerate metric regions reminiscent of the Rankine-Hugoniot conditions. Possible consistency problems with current numerical approaches to black hole dynamics are discussed.