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.

     

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.     

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.     

Gravitational-wave emission from rotating gravitational collapse in three dimensions

We present the first three-dimensional (3D) calculations of the gravitational-wave emission in the collapse of uniformly rotating stars to black holes. The initial models are polytropes which are dynamically unstable and near the mass-shedding limit. The waveforms have been extracted using a gauge-invariant approach and reflect the properties of both the initial stellar models and of newly produced black holes, being in good qualitative agreement with those computed in previous 2D simulations. The wave amplitudes, however, are about 1 order of magnitude smaller, giving, for a source at 10 kpc, a signal-to-noise ratio S/N approximately 0.25 for LIGO-VIRGO and S/N less than or approximately equal 4 for LIGO II.     

Black hole mass threshold from nonsingular quantum gravitational collapse

Quantum gravity is expected to remove the classical singularity that arises as the end state of gravitational collapse. To investigate this, we work with a toy model of a collapsing homogeneous scalar field. We show that nonperturbative semiclassical effects of loop quantum gravity cause a bounce and remove the black hole singularity. Furthermore, we find a critical threshold scale below which no horizon forms: quantum gravity may exclude very small astrophysical black holes.     

Classical and quantum gravitational collapse

The quantization of a homogeneous isotropic closed Friedmann model filled with an ideal fluid is discussed within the framework of a geometrodynamical approach.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 81–86, May, 1977.The authors wish to express their deep indebtedness to B. A. Lysov and A. V. Borisov for their valuable help in the writing of this paper.     

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.     

Gravitational collapse and higher-order gravitational lagrangians

A general form of higher-order contributions (in R_ij) to the Einstein field equations is displayed. The additional terms may either stabilize or destabilize self-gravitating objects in gravitational collapse depending on the sign of the coefficient introducing the quadratic term. If the quadratic term is stabilizing, intertial mass can be converted to radiation with an efficiency approaching 100%, and arbitrarily large masses can be stabilized. On the other hand, the resultant field equations are pathological in that they admit gravitons with negative mass-squared (i.e., tachyons). A nonsingular class of vacuum solutions exist in general for the quadratic case (“grey dimples”).     

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.     

Relativistic gravitational collapse by thermal mass

Gravity and thermal energy are universal phenomena which compete over the stabilization of astrophysical systems.The former induces an inward pressure driving collapse and the latter a stabilizing outward pressure generated by random motion and energy dispersion.Since a contracting self-gravitating system is heated up one may wonder why is gravitational collapse not halted in all cases at a sufficient high temperature establishing either a gravo-thermal equilibrium or explosion.Here,based on the equivalence between mass and energy,we show that there always exists a temperature threshold beyond which the gravitation of thermal energy overcomes its stabilizing pressure and the system collapses under the weight of its own heat.     

Radiating shear-free gravitational collapse with charge

We present here a new shear free model for the gravitational collapse of a spherically symmetric charged body. We propose a dissipative contraction with radiation emitted outwards represented by the Vaidya–Reissner–Nordström metric. The Einstein field equations, using the junction conditions and an ansatz, are integrated numerically. A check of the energy conditions is also performed. We obtain that the charge delays the Reissner–Nordström black hole formation and it can even prevent the collapse.