scholarly journals ON THE RELATIVISTIC GRAVITATIONAL COLLAPSE ET CETERA

2014 ◽  
Author(s):  
Angelo Loinger ◽  
Tiziana Marsico
Keyword(s):  
Internal Pressure ◽  
Observational Data ◽  
Event Horizon ◽  
Gravitational Collapse ◽  
Mass Point ◽  
Finite Volumes

Massive and supermassive “dust” spheres (with a zero internal pressure) collapse to compact “full spheres” of finite volumes, whose surfaces have the properties of the event horizon of a gravitating mass-point. By virtue of Hilbert’s repulsive effect, both the event horizon of a mass-point and the event horizon of a “full sphere” cannot “swallow” anything, in contradiction with the assertion of a locus communis. The observational data corroborate our results.

scholarly journals Meaningless Questions in Cosmology and Relativistic Astrophysics

1976 ◽  
Vol 31 (11) ◽  
pp. 1271-1276 ◽  
Author(s):  
M. Heller ◽  
M. Reinhardt
Keyword(s):  
Event Horizon ◽  
Gravitational Collapse ◽  
Space Time ◽  
Initial Singularity ◽  
Relativistic Astrophysics ◽  
General Classification ◽  
The Universe

Abstract After a general classification of meaningless questions in science we concentrate on empirically meaningless questions. Introducing the concepts of informationally connected, semiconnected and disconnected observers, a formalism for the analysis of the informational structure of space-time is developed. We discuss some problems of epistemological nature in cosmology and blade hole physics. A number of questions like "What was 'before' the initial singularity of the universe?" or "What is the fate of matter in gravitational collapse inside the event horizon?" turn out to be empirically meaningless. We also show that a "wormhole" does not violate causality for the set of informationally connected observers who do not enter it.

scholarly journals Gravitational collapse in the AdS background and the black hole formation

2016 ◽  
Vol 25 (01) ◽  
pp. 1650005 ◽  
Author(s):  
Alireza Allahyari ◽  
Javad T. Firouzjaee ◽  
Reza Mansouri
Keyword(s):  
Black Hole ◽  
Scalar Field ◽  
Event Horizon ◽  
Gravitational Collapse ◽  
Apparent Horizon ◽  
Rapid Change ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Hole Formation ◽  
Thermalization Time

We study the time evolution of the Misner-Sharp mass and the apparent horizon for gravitational collapse of a massless scalar field in the [Formula: see text] spacetime for both cases of narrow and broad waves by numerically solving the Einstein’s equations coupled to a massless scalar field. This is done by relying on the full dynamics of the collapse including the concept of the dynamical horizon. It turns out that the Misner-Sharp mass is everywhere constant except for a rapid change across a thin shell defined by the density profile of the collapsing wave. By studying the evolution of the apparent horizon, indicating the formation of a black hole at different times we see how asymptotically an event horizon forms. The dependence of the thermalization time on the radius of the initial black hole event horizon is also studied.

P-STARS

2004 ◽  
Vol 13 (09) ◽  
pp. 1917-1926 ◽  
Author(s):  
PAOLO CEA
Keyword(s):  
Dark Matter ◽  
Neutron Stars ◽  
Observational Data ◽  
Gravitational Collapse ◽  
Cold Dark Matter ◽  
Compact Stars ◽  
Cooling Curves ◽  
New Class

P-Stars are a new class of compact stars made of up and down quarks in β-equilibrium with electrons in an Abelian chromomagnetic condensate. We show that P-Stars are able to account for compact stars with R≲6 Km , as well as stars with radius comparable with canonical Neutron Stars. We find that cooling curves of P-Stars compare rather well with observational data. We suggest that P-Matter produced at the primordial deconfinement transition is a viable candidate for baryonic Cold Dark Matter. Finally, we show that P-Stars are able to overcome the gravitational collapse even for masses much greater than 106 M⊙.

scholarly journals TESTING THE KERR BLACK HOLE HYPOTHESIS

2011 ◽  
Vol 26 (33) ◽  
pp. 2453-2468 ◽  
Author(s):  
COSIMO BAMBI
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Gravitational Collapse ◽  
State Of The Art ◽  
Kerr Black Hole ◽  
The State ◽  
Kerr Geometry

It is thought that the final product of the gravitational collapse is a Kerr black hole and astronomers have discovered several good astrophysical candidates. While there are some indirect evidences suggesting that the latter have an event horizon, and therefore that they are black holes, a proof that the spacetime around these objects is described by the Kerr geometry is still lacking. Recently, there has been an increasing interest in the possibility of testing the Kerr black hole hypothesis with present and future experiments. In this paper, I briefly review the state-of-the-art of the field, focusing on some recent results and works in progress.

scholarly journals ON THE SOLUTION TO THE "FROZEN STAR" PARADOX, NATURE OF ASTROPHYSICAL BLACK HOLES, NON-EXISTENCE OF GRAVITATIONAL SINGULARITY IN THE PHYSICAL UNIVERSE AND APPLICABILITY OF THE BIRKHOFF'S THEOREM

2011 ◽  
Vol 20 (10) ◽  
pp. 1891-1899 ◽  
Author(s):  
SHUANG-NAN ZHANG
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Gravitational Collapse ◽  
Finite Time ◽  
External Observer ◽  
Gravitational Radius ◽  
Physical Universe ◽  
Gravitational Singularity ◽  
Birkhoff's Theorem ◽  
Birkhoff’S Theorem

Oppenheimer and Snyder found in 1939 that gravitational collapse in vacuum produces a "frozen star", i.e. the collapsing matter only asymptotically approaches the gravitational radius (event horizon) of the mass, but never cross it within a finite time for an external observer. Based upon our recent publication on the problem of gravitational collapse in the physical universe for an external observer, the following results are reported here: (1) Matter can indeed fall across the event horizon within a finite time and thus black holes (BHs), rather than "frozen stars", are formed in gravitational collapse in the physical universe. (2) Matter fallen into an astrophysical BH can never arrive at the exact center; the exact interior distribution of matter depends upon the history of the collapse process. Therefore gravitational singularity does not exist in the physical universe. (3) The metric at any radius is determined by the global distribution of matter, i.e. not only by the matter inside the given radius, even in a spherically symmetric and pressureless gravitational system. This is qualitatively different from the Newtonian gravity and the common (mis)understanding of the Birkhoff's Theorem. This result does not contract the "Lemaitre–Tolman–Bondi" solution for an external observer.

scholarly journals The asymptotic behaviour in Schwarzschild time of Vlasov matter in spherically symmetric gravitational collapse

2010 ◽  
Vol 149 (1) ◽  
pp. 173-188 ◽  
Author(s):  
HÅKAN ANDRÉASSON ◽  
GERHARD REIN
Keyword(s):  
Initial Data ◽  
Asymptotic Behaviour ◽  
Event Horizon ◽  
Gravitational Collapse ◽  
Careful Analysis ◽  
Necessary Condition ◽  
Spherically Symmetric ◽  
Geodesic Completeness ◽  
Global Existence Of Solutions ◽  
Outer Domain

AbstractGiven a static Schwarzschild spacetime of ADM mass M, it is well known that no ingoing causal geodesic starting in the outer domain r > 2M will cross the event horizon r = 2M in finite Schwarzschild time. We show that in gravitational collapse of Vlasov matter this behaviour can be very different. We construct initial data for which a black hole forms and all matter crosses the event horizon as Schwarzschild time goes to infinity, and show that this is a necessary condition for geodesic completeness of the event horizon. In addition to a careful analysis of the asymptotic behaviour of the matter characteristics our proof requires a new argument for global existence of solutions to the spherically symmetric Einstein–Vlasov system in an outer domain, since our initial data have non-compact support in the radial momentum variable and previous methods break down.

Black holes

2021 ◽  
pp. 274-300
Author(s):  
Andrew M. Steane
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Gravitational Collapse ◽  
Symmetric Spaces ◽  
Proper Time ◽  
Cosmic Censorship ◽  
General Nature ◽  
Spherically Symmetric ◽  
Event Horizons ◽  
Killing Horizon

We discuss event horizons and black holes. First Birkhoff’s theorem is derived, and we consider the general nature of spherically symmetric spaces. Then the concepts of null surface, Killing horizon and event horizon are defined and related to one another. Cosmic censorship is briefly discussed. The Schwarzshild horizon is discussed in detail. The divergence or otherwise of redshift, acceleration, speed and proper time is obtained for infalling observers and for Schwarzschild observers. Eddington-Finkelstein coordinates are introduced and used to discuss gravitational collapse. The growth of the horizon is noted, and the causality structure is briefly considered via an introduction to the conformal (Penrose-Carter) diagram. The maximal extension is then presented, with the Kruskal-Szekeres coordinates and associated diagram. Wormholes are briefly discussed. The chapter finishes with a survey of astronomical evidence for black holes.

Optical analogy of gravitational collapse and quantum tunneling of the event horizon

2020 ◽  
Vol 22 (3) ◽  
pp. 035605
Author(s):  
Jingming Chen ◽  
Run-Qiu Yang ◽  
Shining Zhu ◽  
Hui Liu
Keyword(s):  
Event Horizon ◽  
Gravitational Collapse ◽  
Quantum Tunneling ◽  
Optical Analogy

Current status of special planetary and lunar theories and ephemerides

1966 ◽  
Vol 25 ◽  
pp. 266-267
Author(s):  
R. L. Duncombe
Keyword(s):  
Observational Data ◽  
Current Status ◽  
Numerical Errors

An examination of some specialized lunar and planetary ephemerides has revealed inconsistencies in the adopted planetary masses, the presence of non-gravitational terms, and some outright numerical errors. They should be considered of temporary usefulness only, subject to subsequent amendment as required for the interpretation of observational data.

July 11, 1991 Eclipse Corona Photometry by the Results of Electropolarimetric and CCD-Matrix Observations

1994 ◽  
Vol 144 ◽  
pp. 567-569
Author(s):  
V. Kulidzanishvili ◽  
D. Georgobiani
Keyword(s):  
Solar Corona ◽  
Observational Data ◽  
Solar Limb ◽  
Ccd Matrix

AbstractThe observational data of July 11, 1991 eclipse solar corona obtained by both electropolarimeter (EP) and CCD-matrix were processed. Using these data, the solar corona photometry was carried out. The results of EP data are compared with the ones of CCD data. It must be noted here that the CCD data give us only characteristics of the inner corona, while the EP data show the features of both the inner and middle corona up to 4R⊙. Standard flattening indexϵis evaluated from both data. The dependence of the flattening index on the distance from the solar limb is investigated. The isophotes in Na and Ca lines are plotted. Based on these data some ideas and conclusions on the type of the solar corona are presented.

Sign in / Sign up

Export Citation Format

Share Document