scholarly journals GRAVITATIONAL FIELD OF SPHERICAL BRANES

2008 ◽  
Vol 23 (35) ◽  
pp. 2979-2986
Author(s):  
MERAB GOGBERASHVILI
Keyword(s):  
Black Holes ◽  
Gravitational Field ◽  
Analytic Form ◽  
Gravitational Mass ◽  
Moving Frame ◽  
Coordinate Transformations ◽  
Einstein's Equations ◽  
Five Dimensions ◽  
Physical Fields ◽  
Active Gravitational Mass

The warped solution of Einstein's equations corresponding to the spherical brane in five-dimensional AdS is considered. This metric represents interiors of black holes on both sides of the brane and can provide gravitational trapping of physical fields on the shell. It is found that the analytic form of the coordinate transformations from the Schwarzschild to co-moving frame that exists only in five dimensions. It is shown that in the static coordinates active gravitational mass of the spherical brane, in agreement with Tolman's formula, is negative, i.e. such objects are gravitationally repulsive.

Black holes, star clusters, and naked singularities: numerical solution of Einstein’s equations

1992 ◽  
Vol 340 (1658) ◽  
pp. 365-390 ◽  
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Gravitational Field ◽  
Numerical Solution ◽  
Star Clusters ◽  
Particle Simulation ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
Naked Singularities ◽  
Hoop Conjecture

We describe a new method for the numerical solution of Einstein’s equations for the dynamical evolution of a collisionless gas of particles in general relativity. The gravitational field can be arbitrarily strong and particle velocities can approach the speed of light. The computational method uses the tools of numerical relativity and N -body particle simulation to follow the full nonlinear behaviour of these systems. Specifically, we solve the Vlasov equation in general relativity by particle simulation. The gravitational field is integrated by using the 3 + 1 formalism of Arnowitt, Deser and Misner. Physical applications include the stability of relativistic star clusters the binding energy criterion for stability, and the collapse of star clusters to black holes. Astrophysical issues addressed include the possible origin of quasars and active galactic nuclei via the collapse of dense star clusters to supermassive black holes. The method described here also provides a new tool for studying the cosmic censorship hypothesis and the possibility of naked singularities. The formation of a naked singularity during the collapse of a finite object would pose a serious difficulty for the theory of general relativity. The hoop conjecture suggests that this possibility will never happen provided the object is sufficiently compact (≤ M ) in all of its spatial dimensions. But what about the collapse of a long, non-rotating, prolate object to a thin spindle? Such collapse leads to a strong singularity in newtonian gravitation. Using our numerical code to evolve collisionless gas spheroids in full general relativity, we find that in all cases the spheroids collapse to singularities. When the spheroids are sufficiently compact the singularities are hidden inside black holes. However, when the spheroids are sufficiently large there are no apparent horizons. These results lend support to the hoop conjecture and appear to demonstrate that naked singularities can form in asymptotically flat space-times.

Can quantum black holes be (q, p)-fermions?

2017 ◽  
Vol 32 (15) ◽  
pp. 1750080 ◽  
Author(s):  
Emre Dil
Keyword(s):  
Black Holes ◽  
Gravitational Field ◽  
Fermi Gas ◽  
Einstein Equations ◽  
Quantum Corrections ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Entropic Gravity ◽  
Two Parameter

In this study, to investigate the very nature of quantum black holes, we try to relate three independent studies: (q, p)-deformed Fermi gas model, Verlinde’s entropic gravity proposal and Strominger’s quantum black holes obeying the deformed statistics. After summarizing Strominger’s extremal quantum black holes, we represent the thermostatistics of (q, p)-fermions to reach the deformed entropy of the (q, p)-deformed Fermi gas model. Since Strominger’s proposal claims that the quantum black holes obey deformed statistics, this motivates us to describe the statistics of quantum black holes with the (q, p)-deformed fermions. We then apply the Verlinde’s entropic gravity proposal to the entropy of the (q, p)-deformed Fermi gas model which gives the two-parameter deformed Einstein equations describing the gravitational field equations of the extremal quantum black holes obeying the deformed statistics. We finally relate the obtained results with the recent study on other modification of Einstein equations obtained from entropic quantum corrections in the literature.

scholarly journals Black Holes or an Objects without Event Horizon?

2021 ◽  
Author(s):  
Leonid Verozub
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Fermi Gas ◽  
Einstein’S Equations ◽  
Einstein's Equations ◽  
Degenerate Fermi Gas

The paper substantiates the possibility that objects that we usually identify with black holes are self-gravitating, fully or partially degenerate Fermi gas. This follows from the modification of Einstein's equations, which is based on a mathematical fact that the author of the GR could not have known in his time.

Bound orbits around modified Hayward black holes

2021 ◽  
Author(s):  
Bo Gao ◽  
Xue-Mei Deng
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Gravitational Field ◽  
Periodic Orbits ◽  
Kerr Black Hole ◽  
Periodic Oscillations ◽  
Test Particles ◽  
Spin Parameter ◽  
Bound Orbits

The neutral time-like particle’s bound orbits around modified Hayward black holes have been investigated. We find that both in the marginally bound orbits (MBO) and the innermost stable circular orbits (ISCO), the test particle’s radius and its angular momentum are all more sensitive to one of the parameters [Formula: see text]. Especially, modified Hayward black holes with [Formula: see text] could mimic the same ISCO radius around the Kerr black hole with the spin parameter up to [Formula: see text]. Small [Formula: see text] could mimic the ISCO of small-spinning test particles around Schwarzschild black holes. Meanwhile, rational (periodic) orbits around modified Hayward black holes have also been studied. The epicyclic frequencies of the quasi-circular motion around modified Hayward black holes are calculated and discussed with respect to the observed Quasi-periodic oscillations (QPOs) frequencies. Our results show that rational orbits around modified Hayward black holes have different values of the energy from the ones of Schwarzschild black holes. The epicyclic frequencies in modified Hayward black holes have different frequencies from Schwarzschild and Kerr ones. These might provide hints for distinguishing modified Hayward black holes from Schwarzschild and Kerr ones by using the dynamics of time-like particles around the strong gravitational field.

Balancing static vacuum black holes with signed masses in four and five dimensions

2021 ◽  
Vol 104 (4) ◽  
Author(s):  
Marcus Khuri ◽  
Gilbert Weinstein ◽  
Sumio Yamada
Keyword(s):  
Black Holes ◽  
Static Vacuum ◽  
Five Dimensions

3. Extrasolar tests of gravity

2017 ◽  
pp. 35-45
Author(s):  
Timothy Clifton
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Solar System ◽  
Neutron Stars ◽  
Event Horizon ◽  
Gravitational Fields ◽  
Binary Pulsars ◽  
Tests Of Gravity ◽  
Triple Star

By studying objects outside our Solar System, we can observe star systems with far greater gravitational fields. ‘Extrasolar tests of gravity’ considers stars of different sizes that have undergone gravitational collapse, including white dwarfs, neutron stars, and black holes. A black hole consists of a region of space-time enclosed by a surface called an event horizon. The gravitational field of a black hole is so strong that anything that finds its way inside the event horizon can never escape. Other star systems considered are binary pulsars and triple star systems. With the invention of even more powerful telescopes, there will be more tantalizing possibilities for testing gravity in the future.

scholarly journals Atomic stability and the quantum mass equivalence

2019 ◽  
Vol 34 (35) ◽  
pp. 1950293
Author(s):  
Pedro Sancho
Keyword(s):  
Gravitational Field ◽  
Hydrogen Atom ◽  
Equivalence Principle ◽  
Quantum Systems ◽  
Gravitational Mass ◽  
Internal Variables ◽  
Gravitational Fields

We consider an unexplored aspect of the mass equivalence principle in the quantum realm, its connection with atomic stability. We show that if the gravitational mass were different from the inertial one, a Hydrogen atom placed in a constant gravitational field would become unstable in the long term. In contrast, independently of the relation between the two masses, the atom does not become ionized in a uniformly accelerated frame. This work, in the line of previous analyses studying the properties of quantum systems in gravitational fields, contributes to the extension of that program to internal variables.

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