139 research outputs found
Relativistic dynamics of cylindrical shells of counter-rotating particles
Although infinite cylinders are not astrophysical entities, it is possible to
learn a great deal about the basic qualitative features of generation of
gravitational waves and the behavior of the matter conforming such shells in
the limits of very small radius. We describe the analytical model using kinetic
theory for the matter and the junction conditions through the shell to obtain
its equation of motion. The nature of the static solutions are analyzed, both
for a single shell as well as for two concentric shells. In this second case,
for a time dependent external shell, we integrate numerically the equation of
motion for several values of the constants of the system. Also, a brief
description in terms of the Komar mass is given to account for the
gravitational wave energy emitted by the system.Comment: 19 pages, 8 figure
Ejectionâcollision orbits in two degrees of freedom problems in celestial mechanics
The version of record is available online at: http://dx.doi.org/10.1007/s00332-021-09721-5In a general setting of a Hamiltonian system with two degrees of freedom and assuming some properties for the undergoing potential, we study the dynamics close and tending to a singularity of the system which in models of N-body problems corresponds to total collision. We restrict to potentials that exhibit two more singularities that can be regarded as two kind of partial collisions when not all the bodies are involved. Regularizing the singularities, the total collision transforms into a 2-dimensional invariant manifold. The goal of this paper is to prove the existence of different types of ejectionâcollision orbits, that is, orbits that start and end at total collision. Such orbits are regarded as heteroclinic connections between two equilibrium points and are mainly characterized by the partial collisions that the trajectories find on their way. The proof of their existence is based on the transversality of 2-dimensional invariant manifolds and on the behavior of the dynamics on the total collision manifold; both of them are thoroughly described.Peer ReviewedPostprint (author's final draft
Ejection-collision orbits in the symmetric collinear fourâbody problem
In this paper, we consider the collinear symmetric four-body problem, where four masses and aÂż>Âż0, are aligned in this order and move symmetrically about their center of mass. We introduce regularized variables to deal with binary collisions as well as McGehee coordinates to study the quadruple collision manifold for a negative value of the energy. The paper is mainly focused on orbits that eject from (or collide to) quadruple collision. The problem has two hyperbolic equilibrium points, located in the quadruple collision manifold. We use high order parametrizations of their stable/unstable manifolds to devise a numerical procedure to compute ejection-collision orbits, for any value of a. Some results from the explorations done for are presented. Furthermore, we prove the existence of ejection-direct escape orbits, which perform a unique type of binary collisions.Peer ReviewedPostprint (author's final draft
The Effect of Negative-Energy Shells on the Schwarzschild Black Hole
We construct Penrose diagrams for Schwarzschild spacetimes joined by massless
shells of matter, in the process correcting minor flaws in the similar diagrams
drawn by Dray and 't Hooft, and confirming their result that such shells
generate a horizon shift. We then consider shells with negative energy density,
showing that the horizon shift in this case allows for travel between the
heretofore causally separated exterior regions of the Schwarzschild geometry.
These drawing techniques are then used to investigate the properties of
successive shells, joining multiple Schwarzschild regions. Again, the presence
of negative-energy shells leads to a causal connection between the exterior
regions, even in (some) cases with two successive shells of equal but opposite
total energy.Comment: 12 pages, 10 figure
Gravitational Collapse of Cylindrical Shells Made of Counter-Rotating Dust Particles
The general formulas of a non-rotating dynamic thin shell that connects two
arbitrary cylindrical regions are given using Israel's method. As an
application of them, the dynamics of a thin shell made of counter-rotating dust
particles, which emits both gravitational waves and massless particles when it
is expanding or collapsing, is studied. It is found that when the models
represent a collapsing shell, in some cases the angular momentum of the dust
particles is strong enough to halt the collapse, so that a spacetime
singularity is prevented from forming, while in other cases it is not, and a
line-like spacetime singularity is finally formed on the symmetry axis.Comment: To appear in Phys. Rev.
Evolution of thin-wall configurations of texture matter
We consider the free matter of global textures within the framework of the
perfect fluid approximation in general relativity. We examine thermodynamical
properties of texture matter in comparison with radiation fluid and bubble
matter. Then we study dynamics of thin-wall selfgravitating texture objects,
and show that classical motion can be elliptical (finite), parabolical or
hyperbolical. It is shown that total gravitational mass of neutral textures in
equilibrium equals to zero as was expected. Finally, we perform the
Wheeler-DeWitt's minisuperspace quantization of the theory, obtain exact wave
functions and discrete spectra of bound states with provision for spatial
topology.Comment: intermediate research on nature of dual-radiation matter; LaTeX, 12
pages, 1 figure and epsfig style file included; slightly shortened version
was published in December issue of GR
Black hole mimickers: regular versus singular behavior
Black hole mimickers are possible alternatives to black holes, they would
look observationally almost like black holes but would have no horizon. The
properties in the near-horizon region where gravity is strong can be quite
different for both type of objects, but at infinity it could be difficult to
discern black holes from their mimickers. To disentangle this possible
confusion, we examine the near-horizon properties, and their connection with
far away properties, of some candidates to black mimickers. We study
spherically symmetric uncharged or charged but non-extremal objects, as well as
spherically symmetric charged extremal objects. Within the uncharged or charged
but non-extremal black hole mimickers, we study non-extremal
-wormholes on the threshold of the formation of an event horizon, of
which a subclass are called black foils, and gravastars. Within the charged
extremal black hole mimickers we study extremal -wormholes on the
threshold of the formation of an event horizon, quasi-black holes, and
wormholes on the basis of quasi-black holes from Bonnor stars. We elucidate,
whether or not the objects belonging to these two classes remain regular in the
near-horizon limit. The requirement of full regularity, i.e., finite curvature
and absence of naked behavior, up to an arbitrary neighborhood of the
gravitational radius of the object enables one to rule out potential mimickers
in most of the cases. A list ranking the best mimickers up to the worse is
given. Since, in observational astrophysics it is difficult to find extremal
configurations (the best mimickers in the ranking), whereas non-extremal
configurations are really bad mimickers, the task of distinguishing black holes
from their mimickers seems to be less difficult than one could think of.Comment: 30 pages, 1 figure, references added, minor changes in the revised
versio
Critical phenomena of collapsing massless scalar wave packets
An analytical model that represents the collapse of a massless scalar wave
packet with continuous self-similarity is constructed, and critical phenomena
are found. In the supercritical case, the mass of black holes is finite and has
the form , with .Comment: Latex file, including 2 figures, avalaible upon reques
Radiation fluid singular hypersurfaces with de Sitter interior as models of charged extended particles in general relativity
In present paper we construct the classical and minisuperspace quantum models
of an extended charged particle. The modelling is based on the radiation fluid
singular hypersurface filled with physical vacuum. We demonstrate that both at
classical and quantum levels such a model can have equilibrium states at the
radius equal to the classical radius of a charged particle. In the cosmological
context the model could be considered also as the primary stationary state,
having the huge internal energy being nonobservable for an external observer,
from which the Universe was born by virtue of the quantum tunnelling.Comment: LaTeX (IOPP style); final versio
Generalized Vaidya Solutions
A large family of solutions, representing, in general, spherically symmetric
Type II fluid, is presented, which includes most of the known solutions to the
Einstein field equations, such as, the monopole-de Sitter-charged Vaidya ones.Comment: Gen. Relativ. Grav. 31 (1), 107-114 (1999
- âŠ