67 research outputs found
Developments in General Relativity: Black Hole Singularity and Beyond
At the 20-th Texas Symposium on Relativistic Astrophysics there was a plenary
talk devoted to the recent developments in classical Relativity. In that talk
the problems of gravitational collapse, collisions of black holes, and of black
holes as celestial bodies were discussed. But probably the problems of the
internal structure of black holes are a real great challenge. In my talk I want
to outline the recent achievements in our understanding of the nature of the
singularity (and beyond!) inside a realistic rotating black hole. This
presentation also addresses the following questions: Can we see what happens
inside a black hole? Can a falling observer cross the singularity without being
crushed? An answer to these questions is probably "yes".Comment: 13 page
Three-Dimensional Billiards with Time Machine
Self-collision of a non-relativistic classical point-like body, or particle,
in the spacetime containing closed time-like curves (time-machine spacetime) is
considered. A point-like body (particle) is an idealization of a small ideal
elastic billiard ball. The known model of a time machine is used containing a
wormhole leading to the past. If the body enters one of the mouths of the
wormhole, it emerges from another mouth in an earlier time so that both the
particle and its "incarnation" coexist during some time and may collide. Such
self-collisions are considered in the case when the size of the body is much
less than the radius of the mouth, and the latter is much less than the
distance between the mouths. Three-dimensional configurations of trajectories
with a self-collision are presented. Their dynamics is investigated in detail.
Configurations corresponding to multiple wormhole traversals are discussed. It
is shown that, for each world line describing self-collision of a particle,
dynamically equivalent configurations exist in which the particle collides not
with itself but with an identical particle having a closed trajectory (Jinnee
of Time Machine).Comment: 20 pages (LATEX), 5 figures (EPS
Silhouettes of wormholes traversed for radiation
The problem of the passage of light through the mouth of a zero-mass wormhole
and the possibility of observing the objects from another asymptotically flat
space-time through the mouth of a wormhole are considered. It is shown that an
individual star can have several images and the fact that the image of a flat
Lambertian screen has a complex brightness distribution for an observer located
on the opposite side of the throat. Images of two such screens visible inside
the silhouette of a massless wormhole and the distribution of radiation
intensity in their images are constructed.Comment: 11 pages, 12 figure
Homogeneous singularities inside collapsing wormholes
We analyze analytically and numerically the origin of the singularity in the
course of the collapse of a wormhole with the exotic scalar field Psi with
negative energy density, and with this field Psi together with the ordered
magnetic field H. We do this under the simplifying assumptions of the spherical
symmetry and that in the vicinity of the singularity the solution of the
Einstein equations depends only on one coordinate (the homogeneous
approximation). In the framework of these assumptions we found the principal
difference between the case of the collapse of the ordinary scalar field Phi
with the positive energy density together with an ordered magnetic field H and
the collapse of the exotic scalar field Psi together with the magnetic field H.
The later case is important for the possible astrophysical manifestation of the
wormholes.Comment: 10 pages, 5 figures each of which has a),b),c),and d) sub-figures. To
be published in "Physical review. D, Particles, fields, gravitation, and
cosmology
Numerical simulations of wind-driven protoplanetary nebulae – I. near-infrared emission
To understand how the circumstellar environments of post-Active Giant Branch (AGB) stars develop into planetary nebulae, we initiate a systematic study of 2D axisymmetric hydrodynamic simulations of protoplanetary nebula (pPN) with a modified ZEUS code. The aim of this first work is to compare the structure of prolate ellipsoidal winds into a stationary ambient medium where both media can be either atomic or molecular. We specifically model the early twin-shock phase which generates a decelerating shell. A thick deformed and turbulent shell grows when an atomic wind expands into an atomic medium. In all other cases, the interaction shell region fragments into radial protrusions due to molecular cooling and chemistry. The resulting fingers eliminate any global slip parallel to the shell surface. This rough surface implies that weak shocks are prominent in the excitation of the gas despite the fast speed of advance. This may explain why low-excitation molecular hydrogen is found towards the front of elliptical pPN. We constrain molecular dissociative fractions and time-scales of fast H2 winds and the pPN lifetime with wind densities ∼105cm−3 and shock speeds of 80∼200kms−1. We identify a variety of stages associated with thermal excitation of H2 near-infrared emission. Generated line emission maps and position–velocity diagrams enable a comparison and distinction with post-AGB survey results. The 1→0S(1)&2→1S(1) lines are lobe-dominated bows rather than bipolar shells
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