scholarly journals GENERICITY ASPECTS IN GRAVITATIONAL COLLAPSE TO BLACK HOLES AND NAKED SINGULARITIES

2012 ◽  
Vol 21 (08) ◽  
pp. 1250066 ◽  
Author(s):  
PANKAJ S. JOSHI ◽  
DANIELE MALAFARINA ◽  
RAVINDRA V. SARAYKAR
Keyword(s):  
Black Holes ◽  
Initial Data ◽  
Gravitational Collapse ◽  
Naked Singularity ◽  
Matter Field ◽  
Einstein Equations ◽  
Type I ◽  
Naked Singularities ◽  
Physical Conditions ◽  
Perfect Fluids

Here we investigate the genericity and stability aspects for naked singularities and black holes that arise as the final states for a complete gravitational collapse of a spherical massive matter cloud. The form of the matter considered is a general Type I matter field, which includes most of the physically reasonable matter fields such as dust, perfect fluids and such other physically interesting forms of matter widely used in gravitation theory. Here, we first study in some detail the effects of small pressure perturbations in an otherwise pressure-free collapse scenario, and examine how a collapse evolution that was going to the black hole endstate would be modified and go to a naked singularity, once small pressures are introduced in the initial data. This allows us to understand the distribution of black holes and naked singularities in the initial data space. Collapse is examined in terms of the evolutions allowed by Einstein equations, under suitable physical conditions and as evolving from a regular initial data. We then show that both black holes and naked singularities are generic outcomes of a complete collapse, when genericity is defined in a suitable sense in an appropriate space.

scholarly journals CAN WE SEE NAKED SINGULARITIES?

2009 ◽  
Vol 18 (14) ◽  
pp. 2083-2092
Author(s):  
SHRIRANG S. DESHINGKAR
Keyword(s):  
Initial Data ◽  
Gravitational Collapse ◽  
Energy Condition ◽  
Matter Field ◽  
Specific Form ◽  
Weak Energy Condition ◽  
Spherically Symmetric ◽  
Naked Singularities ◽  
Physical Consequences

We study singularities which can form in a spherically symmetric gravitational collapse of a general matter field obeying weak energy condition. We show that null naked singularities that form in such a collapse can never be observed. No energy can come out of these singularities; thus they will have no physical consequences outside. As this happens for any null singularity, we do not need to assume specific form of matter and establish role of initial data. Hence our result is very general.

scholarly journals NAKED SINGULARITIES AS CANDIDATES FOR GAMMA-RAY BURSTERS

1994 ◽  
Vol 03 (03) ◽  
pp. 647-651 ◽  
Author(s):  
SANDIP K. CHAKRABARTI ◽  
PANKAJ S. JOSHI
Keyword(s):  
Gravitational Waves ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Naked Singularity ◽  
Shift Factor ◽  
Red Shift ◽  
Einstein Equations ◽  
Pure Radiation ◽  
Naked Singularities ◽  
Perfect Fluids

Naked singularities appear naturally in dynamically evolving solutions of Einstein equations involving gravitational collapse of radiation, dust, and perfect fluids provided the rate of accretion is less than a critical value. We propose that the gamma-ray bursters (GRBs) are examples of these naked singularity solutions. For illustration, we show that according to solutions involving spherically symmetric collapse of pure radiation field, the energy Eγ and the observed duration Δt0 of a GRB should satisfy, [Formula: see text] being the fraction (10−2 to 10−3) of energy released as gamma rays and the rest possibly as gravitational waves. All the presently observed GRBs satisfy this condition; those satisfying the condition close to equality must necessarily be of cosmological origin with the red-shift factor z not exceeding ~1−10 depending on exact observed flux, red-shift and conversion efficiency of gamma rays. If GRBs are indeed from naked singular regions, they should also be accompanied by a strong burst of gravitational waves which, if detectible, will constitute a basic test for our model.

scholarly journals RECENT DEVELOPMENTS IN GRAVITATIONAL COLLAPSE AND SPACETIME SINGULARITIES

2011 ◽  
Vol 20 (14) ◽  
pp. 2641-2729 ◽  
Author(s):  
PANKAJ S. JOSHI ◽  
DANIELE MALAFARINA
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Collapse ◽  
Spacetime Singularities ◽  
Black Hole Physics ◽  
Naked Singularity ◽  
Theory Of Relativity ◽  
Quantum Theories ◽  
Naked Singularities ◽  
Astrophysical Objects

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.

The eternal naked singularity formation in the case of gravitational collapse of generalized Vaidya space–time

2018 ◽  
Vol 33 (17) ◽  
pp. 1850102 ◽  
Author(s):  
Vitalii Vertogradov
Keyword(s):  
Gravitational Collapse ◽  
Negative Pressure ◽  
Apparent Horizon ◽  
Naked Singularity ◽  
Space Time ◽  
Matter Field ◽  
Type I ◽  
The Past ◽  
Central Singularity ◽  
Short Time

In this paper, we consider the gravitational collapse of generalized Vaidya space–time when the matter satisfies the equation of the state either [Formula: see text] or [Formula: see text], where [Formula: see text]. We show that in the case when type I of matter field is dust, then the apparent horizon will never appear but there is no a family of null radial future-directed geodesics which terminate at the central singularity in the past. Also, we show that in the case of negative pressure, the result of the gravitational collapse might be the naked singularity and the apparent horizon appears and in very short time disappears again. In the case of the negative pressure, we show that the result of the gravitational collapse might be the eternal naked singularity.

scholarly journals The Negative Energy in Generalized Vaidya Spacetime

Universe ◽  
2020 ◽  
Vol 6 (9) ◽  
pp. 155
Author(s):  
Vitalii Vertogradov
Keyword(s):  
Gravitational Collapse ◽  
Naked Singularity ◽  
Negative Energy ◽  
Matter Field ◽  
The State ◽  
Energy Problem

In this paper we consider the negative energy problem in generalized Vaidya spacetime. We consider several models where we have the naked singularity as a result of the gravitational collapse. In these models we investigate the geodesics for particles with negative energy when the II type of the matter field satisfies the equation of the state P=αρ (α∈[0,1]).

scholarly journals NONSTATIC CHARGED BTZ-LIKE BLACK HOLES IN N+1 DIMENSIONS

2012 ◽  
Vol 21 (03) ◽  
pp. 1250022 ◽  
Author(s):  
SUSHANT G. GHOSH
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Collapse ◽  
Naked Singularity ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Btz Black Hole ◽  
Sitter Spacetime ◽  
Apparent Horizons ◽  
Sitter Background

We find an exact nonstatic charged BTZ-like solutions, in (N+1)-dimensional Einstein gravity in the presence of negative cosmological constant and a nonlinear Maxwell field defined by a power s of the Maxwell invariant, which describes the gravitational collapse of charged null fluid in an anti-de Sitter background. Considering the situation that a charged null fluid injects into the initially an anti-de Sitter spacetime, we show that a black hole form rather than a naked singularity, irrespective of spacetime dimensions, from gravitational collapse in accordance with cosmic censorship conjecture. The structure and locations of the apparent horizons of the black holes are also determined. It is interesting to see that, in the static limit and when N = 2, one can retrieve 2+1 BTZ black hole solutions.

scholarly journals A DYNAMICAL SYMMETRY OF THE QUASI-SPHERICAL (OR SPHERICAL) COLLAPSE

2005 ◽  
Vol 14 (10) ◽  
pp. 1761-1767 ◽  
Author(s):  
UJJAL DEBNATH ◽  
SUBENOY CHAKRABORTY ◽  
NARESH DADHICH
Keyword(s):  
Kinetic Energy ◽  
Initial Data ◽  
Dynamical Symmetry ◽  
Matter Field ◽  
Physical Parameters ◽  
Data Sets ◽  
Type I ◽  
Data Set ◽  
Spherical Collapse ◽  
Scaling Relationship

By linearly scaling the initial data set (mass and kinetic energy functions), it is found that the dynamics of quasi-spherical (or spherical) collapse remains invariant for dust or a general (Type I) matter field, provided the comoving radius is also appropriately scaled. This defines a symmetry of the quasi spherical (or spherical) collapse. That is, the linear transformation identifies an equivalence class of data sets which lead to the same end result as well as its evolution all through. In particular, it is shown that the physical parameters, density and shear remain invariant. What the transformation is exhibiting is an interesting scaling relationship between mass, kinetic energy and the size of the collapsing sphere which is respected not only by the initial data set but remarkably also by the dynamics of collapse.

scholarly journals Stability of naked singularity arising in gravitational collapse of Type I matter fields

Pramana ◽  
2005 ◽  
Vol 65 (1) ◽  
pp. 17-33 ◽  
Author(s):  
Sanjay B. Sarwe ◽  
R. V. Saraykar
Keyword(s):  
Gravitational Collapse ◽  
Naked Singularity ◽  
Type I ◽  
Matter Fields

scholarly journals GRAVITATIONAL COLLAPSE OF SPHERICALLY SYMMETRIC PERFECT FLUID WITH KINEMATIC SELF-SIMILARITY

2002 ◽  
Vol 11 (02) ◽  
pp. 155-186 ◽  
Author(s):  
C. F. C. BRANDT ◽  
L.-M. LIN ◽  
J. F. VILLAS DA ROCHA ◽  
A. Z. WANG
Keyword(s):  
Black Holes ◽  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Spherically Symmetric ◽  
De Sitter ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Self Similarity ◽  
Schwarzschild Solution ◽  
Naked Singularities

Analytic spherically symmetric solutions of the Einstein field equations coupled with a perfect fluid and with self-similarities of the zeroth, first and second kinds, found recently by Benoit and Coley [Class. Quantum Grav.15, 2397 (1998)], are studied, and found that some of them represent gravitational collapse. When the solutions have self-similarity of the first (homothetic) kind, some of the solutions may represent critical collapse but in the sense that now the "critical" solution separates the collapse that forms black holes from the collapse that forms naked singularities. The formation of such black holes always starts with a mass gap, although the "critical" solution has homothetic self-similarity. The solutions with self-similarity of the zeroth and second kinds seem irrelevant to critical collapse. Yet, it is also found that the de Sitter solution is a particular case of the solutions with self-similarity of the zeroth kind, and that the Schwarzschild solution is a particular case of the solutions with self-similarity of the second kind with the index α=3/2.

scholarly journals GENERATING STATIC, SPHERICALLY SYMMETRIC BLACK HOLES IN LOVELOCK GRAVITY

2009 ◽  
Vol 18 (13) ◽  
pp. 2061-2082 ◽  
Author(s):  
S. HABIB MAZHARIMOUSAVI ◽  
O. GURTUG ◽  
M. HALILSOY
Keyword(s):  
Black Holes ◽  
Higher Dimensions ◽  
Matter Field ◽  
Spherically Symmetric ◽  
Lovelock Gravity ◽  
Third Order ◽  
Naked Singularities ◽  
Test Particles ◽  
Higher Dimensional ◽  
Symmetric Black Hole

We present the generalization of a known theorem to generate static, spherically symmetric black hole solutions in higher-dimensional Lovelock gravity. Particular limits such as Gauss–Bonnet (GB) and Einstein–Hilbert (EH) in any dimension N yield all the solutions known to date with an energy–momentum. In our generalization, with special emphasis on third order Lovelock gravity, we have found two different class of solutions characterized by the matter field parameter. Several particular cases are studied and properties related to asymptotic behaviors are discussed. Our general solution, which covers topological black holes as well, splits naturally into distinct classes such as Chern–Simon (CS) and Born–Infeld (BI) in higher-dimensions. The occurence of naked singularities is studied and it is found that the space–time behaves nonsingularly in the quantum-mechanical sense when it is probed with quantum test particles. The theorem is extended to cover Bertotti–Robinson (BR) type solutions in the presence of the GB parameter alone. Finally, we prove also that extension of the theorem for a scalar–tensor source of higher dimensions (N > 4) fails to work.

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