4 research outputs found
Bounds on the mass-to-radius ratio for non-compact field configurations
It is well known that a spherically symmetric compact star whose energy
density decreases monotonically possesses an upper bound on its mass-to-radius
ratio, . However, field configurations typically will not be
compact. Here we investigate non-compact static configurations whose matter
fields have a slow global spatial decay, bounded by a power law behavior. These
matter distributions have no sharp boundaries. We derive an upper bound on the
fundamental ratio max_r{2m(r)/r} which is valid throughout the bulk. In its
simplest form, the bound implies that in any region of spacetime in which the
radial pressure increases, or alternatively decreases not faster than some
power law , one has . [For
the bound degenerates to .] In its general version, the bound
is expressed in terms of two physical parameters: the spatial decaying rate of
the matter fields, and the highest occurring ratio of the trace of the pressure
tensor to the local energy density.Comment: 4 page
Surface stresses on a thin shell surrounding a traversable wormhole
We match an interior solution of a spherically symmetric traversable wormhole
to a unique exterior vacuum solution, with a generic cosmological constant, at
a junction interface, and the surface stresses on the thin shell are deduced.
In the spirit of minimizing the usage of exotic matter we determine regions in
which the weak and null energy conditions are satisfied on the junction
surface. The characteristics and several physical properties of the surface
stresses are explored, namely, regions where the sign of the tangential surface
pressure is positive and negative (surface tension) are determined. This is
done by expressing the tangential surface pressure as a function of several
parameters, namely, that of the matching radius, the redshift parameter, the
surface energy density and of the generic cosmological constant. An equation
governing the behavior of the radial pressure across the junction surface is
also deduced.Comment: 24 pages, 11 figures, LaTeX2e, IOP style files. Accepted for
publication in Classical and Quantum Gravity. V2: Four references added, now
25 page
Generic thin-shell gravastars
We construct generic spherically symmetric thin-shell gravastars by using the
cut-and-paste procedure. We take considerable effort to make the analysis as
general and unified as practicable; investigating both the internal physics of
the transition layer and its interaction with "external forces" arising due to
interactions between the transition layer and the bulk spacetime. Furthermore,
we discuss both the dynamic and static situations. In particular, we consider
"bounded excursion" dynamical configurations, and probe the stability of static
configurations. For gravastars there is always a particularly compelling
configuration in which the surface energy density is zero, while surface
tension is nonzero.Comment: V1: 39 pages, 9 figures; V2: 40 pages, 9 figures. References added,
some discussion added, some typos fixed. Identical to published version.
arXiv admin note: text overlap with arXiv:1112.205