Relaxation dynamics of charged gravitational collapse

We study analytically the relaxation dynamics of charged test fields left outside a newly born charged black hole. In particular, we obtain a simple analytic expression for the fundamental quasinormal resonances of near-extremal Reissner-Nordström black holes. The formula is expressed in terms of the black-hole physical parameters: , where TBH and Φ are the temperature and electric potential of the black hole, and q is the charge of the field.     

Entropy change in axial symmetric gravitational collapse

We calculate the entropy changes of an imperfect-fluid gravitational collapsing system in the axial symmetric situation, analyzing a practical example. We conclude that the entropy of the collapsing system decreases at the beginning of the collapse and then increases very near the system's horizon.     

Non-adiabatic gravitational collapse of charged radiating fluid spheres

Dynamical equations governing the non-adiabatic collapse of a shear-free spherical distribution of unisotropic matter in the presence of charge are obtained. A brief outline of constructing a model describing collapse of a charged radiating fluid sphere in the set up developed is given.     

Naked singularities in spherically symmetric gravitational collapse: A critique

One of the most important questions in the physics of gravitation phenomena is whether gravitational collapse can lead to the formation of singularities which are not hidden by an event horizon. The Cosmic Censorship Conjecture (CCC) represents the hope that such a drastic event cannot happen in realistic physical situations. However, in the recent past several counter examples to the CCC were demonstrated by several researchers in situations of spherically symmetric gravitational collapse. The disturbing aspect about these counter examples is that they are strong naked singularities—they can crush matter to zero volume and can have a disastrous influence on causal physics. We examine these counter examples for their physical content by working through the dynamical collapse of inhomogeneous dust and argue that these are not physically acceptable counter examples. Our main result is that the singularities when naked are weak and when strong, strongly censored. The strong naked singularities in the counter examples do not arise from dynamical collapse; they result from the intrinsically singular nature of the initial density distributions chosen. The CCC seems to remain robust as far as spherically symmetric collapse is concerned.     

On the occurrence of naked singularity in spherically symmetric gravitational collapse

Generalizing earlier results of [1], we analyze here the spherically symmetric gravitational collapse of a matter cloud with a general form of matter for the formation of a naked singularity. It is shown that this is related basically to the choice of initial data to the Einstein field equations, and would therefore occur in generic situations from regular initial data within the general context considered here, subject to the matter satisfying the weak energy condition. The condition on initial data which leads to the formation of black hole is also characterized.     

Prevention of gravitational collapse

We apply a new theory of gravitation to the question of gravitational collapse to show that collapse is prevented in this theory under very reasonable conditions. This result also extends to prevent ultimate collapse of the Universe.     

Dynamics of a charged particle in a progressive plane wave

The dynamics of a charged particle in a relativistic strong electromagnetic plane wave propagating in a medium is studied. The problem is shown to be integrable when the wave propagates in vacuum. When it propagates in plasma, and when the full plasma response is considered, an exhaustive numerical work allows us to conclude that the problem is not integrable.     

Photinos from gravitational collapse

Very light photinos, if they exist, should be produced in a SN explosion. Using the data from SN 1987A we set limits on the masses of selectrons (and squarks), the SUSY particles involved in the production (and diffusion) of photinos in the stellar medium. The bounds obtained are

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, where .     

Neutrinos from gravitational collapse

Summary A review is made of neutrino fluxes produced by gravitational collapse events (type-II supernovae?). Recent work of Mayle, Wilson and Schramm is used to examine those aspects of neutrino signal which are relatively independent of the collapse model and those aspects which are sensitive to model details. A discussion of the antineutrino background from the integral of all collapse events is also presented.

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Riassunto Si esaminano i flussi di neutrini prodotti da eventi di collasso gravitazionale (supernovae di tipo II?). Si usa il lavoro recente di Mayle, Wilson e Schramm per esaminare quegli aspetti del segnale del neutrino che sono relativamente indipendenti dal modello del collasso e quegli aspetti che sono sensibili ai dettagli del modello. Si presenta anche una discussione del background di antineutrini dall'integrale di tutti gli eventi di collasso.

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Резюме Анализируются нейтринные потоки, образованные в результате гравитационного коллапса. Недавняя табота Мейла, Вильсона и Шрамма используется для изучения таких аспектов нейтринного сигнала, которые не зависят от модели коллапса, а также таких аспектов, которые являются чувствительными к деталям модели. Проводится обсужление фона анти-нейтрино, исходя из интеграла всех событий коллапса.

     

Exact plane symmetric solutions of sin-Gordon equations with inherent gravitational fields taken into account

We obtain exact self-consistent plane symmetric solutions to systems of Einstein equations and nonlinear scalar field equations of sin-Gordon type. We write out, in explicit from, two specific solutions corresponding to specific choices of the nonlinearity parameter λ. We show that for each value of λ, there exist solutions of soliton and antisoliton type with topological charge Q=±1. We establish that the basic difference between the solutions we obtain and solutions of the sin-Gordon equation in flat space—time is that when we take internal gravitational fields into account, each value of λ corresponds to a specific function ϕ_λ(x). Russian Peoples' Friendship University. Translated from Izvestiya Vysshikh Uchebnikh Zavedenii, Fizika, No. 10, pp. 87–93, October, 1996.     

Model of internal gravitational collapse

The concept of internal gravitational collapse is introduced, and the metrics associated with an initially collapsing sphere and the collapse of a spherical layer are found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 47–50, August, 1974.     

Quantum mechanics of gravitational collapse

A toy model of gravitational collapse in General Relativity is studied. It consists of a spherically symmetric thin shell of dust with a fixed rest mass. The configuration space is the half-axis and the Hamiltonian splits into a differential operator of infinite order (free Hamiltonian) and a Coulomb potential. Harmonic analysis on the half-axis is used to define the free Hamiltonian. For rest masses comparable to, or lower than one Planck mass, the Kato-Rellich theorem is applicable and one self-adjoint extension of the full Hamiltonian is found. A boundary condition for the wave function results whose effect is to keep the shell away from the singularity. This will lead to superposition of states containing both black and white holes.     

Can quantum gravitational forces stop gravitational collapse?

We consider, in lowest order of the gravitational coupling constant G, the gravitational potential between two neutrons. As we have previously pointed out [1],the quantum (including spin) contributions to the gravitational field dominate for distances smaller than the Compton wavelength of the neutron. At such distances the gravitational force between two neutrons may be repulsive. In particular, the gravitational forces which are analogous to the familiar Darwin and Fermi forces of quantum electrodynamics are capable of stopping gravitational collapse. Our discussion is within the framework of Einstein's theory, but on a microscopic level. We conclude that gravitational collapse may be halted without the necessity of extending Einstein's theory à la Cartan or otherwise.