301 research outputs found
Gravitational Radiation from Cylindrical Naked Singularity
We construct an approximate solution which describes the gravitational
emission from a naked singularity formed by the gravitational collapse of a
cylindrical thick shell composed of dust. The assumed situation is that the
collapsing speed of the dust is very large. In this situation, the metric
variables are obtained approximately by a kind of linear perturbation analysis
in the background Morgan solution which describes the motion of cylindrical
null dust. The most important problem in this study is what boundary conditions
for metric and matter variables should be imposed at the naked singularity. We
find a boundary condition that all the metric and matter variables are
everywhere finite at least up to the first order approximation. This implies
that the spacetime singularity formed by this high-speed dust collapse is very
similar to that formed by the null dust and thus the gravitational emission
from a naked singularity formed by the cylindrical dust collapse can be gentle.Comment: 20 pages, 1 figur
Identification of an expanded binding surface on the FADD death domain responsible for interaction with CD95/Fas
The initiation of programmed cell death at CD95 (Fas, Apo-1) is achieved by forming a death-inducing signaling complex (DISC) at the cytoplasmic membrane surface. Assembly of the DISC has been proposed to occur via homotypic interactions between the death domain (DD) of FADD and the cytoplasmic domain of CD95. Previous analysis of the FADD/CD95 interaction led to the identification of a putative CD95 binding surface within FADD DD formed by alpha helices 2 and 3. More detailed analysis of the CD95/FADD DD interaction now demonstrates that a bimodal surface exists in the FADD DD for interaction with CD95. An expansive surface on one side of the domain is composed of elements in alpha helices 1, 2, 3, 5, and 6. This major surface is common to many proteins harboring this motif, whether or not they are associated with programmed cell death. A secondary surface resides on the opposite face of the domain and involves residues in helices 3 and 4. The major surface is topologically similar to the protein interaction surface identified in Drosophila Tube DD and the death effector domain of hamster PEA-15, two physiologically unrelated proteins which interact with structurally unrelated binding partners. These results demonstrate the presence of a structurally conserved surface within the DD which can mediate protein recognition with homo- and heterotypic binding partners, whereas a second surface may be responsible for stabilizing the higher order complex in the DISC
Topology Change of Coalescing Black Holes on Eguchi-Hanson Space
We construct multi-black hole solutions in the five-dimensional
Einstein-Maxwell theory with a positive cosmological constant on the
Eguchi-Hanson space, which is an asymptotically locally Euclidean space. The
solutions describe the physical process such that two black holes with the
topology of S^3 coalesce into a single black hole with the topology of the lens
space L(2;1)=S^3/Z_2. We discuss how the area of the single black hole after
the coalescence depends on the topology of the horizon.Comment: 10 pages, Some comments are added. to be published as a letter in
Classical and Quantum Gravit
Energy flux through the horizon in the black hole-domain wall systems
We study various configurations in which a domain wall (or cosmic string),
described by the Nambu-Goto action, is embedded in a background space-time of a
black hole in and higher dimensional models. We calculate energy fluxes
through the black hole horizon. In the simplest case, when a static domain wall
enters the horizon of a static black hole perperdicularly, the energy flux is
zero. In more complicated situations, where parameters which describe the
domain wall surface are time and position dependent, the flux is non-vanishing
is principle. These results are of importance in various conventional
cosmological models which accommodate the existence of domain walls and strings
and also in brane world scenarios.Comment: references added, accepted for publication in JHE
Thick domain walls around a black hole
We discuss the gravitationally interacting system of a thick domain wall and
a black hole. We numerically solve the scalar field equation in the
Schwarzschild spacetime and obtain a sequence of static axi-symmetric solutions
representing thick domain walls. We find that, for the walls near the horizon,
the Nambu--Goto approximation is no longer valid.Comment: 18 pages, 11 figures, one reference adde
Uniqueness Theorem for Black Hole Space-Times with Multiple Disconnected Horizons
We show uniqueness of stationary and asymptotically flat black hole
space-times with multiple disconnected horizons and with two rotational Killing
vector fields in the context of five-dimensional minimal supergravity
(Einstein-Maxwell-Chern-Simons gravity). The novelty in this work is the
introduction in the uniqueness theorem of intrinsic local charges measured near
each horizon as well as the measurement of local fluxes besides the asymptotic
charges that characterize a particular solution. A systematic method of
defining the boundary conditions on the fields that specify a black hole
space-time is given based on the study of its rod structure (domain structure).
Also, an analysis of known solutions with disconnected horizons is carried out
as an example of an application of this theorem.Comment: 28 pages, 5 figures. v3: Further improvements on uniqueness theorem,
Lemma introduced for clarity of derivation, new quantities introduced to
treat special case with zero flux, refs. added, typos fixe
The hardest X-ray source in the ASCA Large Sky Survey: Discovery of a new type 2 Seyfert
We present results of ASCA deep exposure observations of the hardest X-ray
source discovered in the ASCA Large Sky Survey (LSS) project, designated as AX
J131501+3141. We extract its accurate X-ray spectrum, taking account of the
contamination from a nearby soft source (AX J131502+3142), separated only by
1'. AX J131501+3141 exhibits a large absorption of NH = (6 +4 -2)x 10^22 H/cm^2
with a photon index \Gamma = 1.5 +0.7 -0.6. The 2--10 keV flux was about 5 x
10^-13 erg/s/cm^2 and was time variable by a factor of 30% in 0.5 year. From
the highly absorbed X-ray spectrum and the time variability, as well as the
results of the optical follow-up observations (Akiyama et al. 1998,
astro-ph/9801173), we conclude that AX J131501+3141 is a type 2 Seyfert galaxy.
Discovery of such a low flux and highly absorbed X-ray source could have a
significant impact on the origin of the cosmic X-ray background.Comment: 16 pages, 6 figures, requires AAS Latex macro v4.0, to appear in The
Astrophysical Journal, text and figures also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/sakano/work/paper/index-e.htm
High Speed Dynamics of Collapsing Cylindrical Dust Fluid
We construct approximate solutions that will describe the last stage of
cylindrically symmetric gravitational collapse of dust fluid. Just before the
spacetime singularity formation, the speed of the dust fluid might be almost
equal to the speed of light by gravitational acceleration. Therefore the
analytic solution describing the dynamics of cylindrical null dust might be the
crudest approximate solution of the last stage of the gravitational collapse.
In this paper, we regard this null dust solution as a background and perform
`high-speed approximation' to know the gravitational collapse of ordinary
timelike dust fluid; the `deviation of the timelike
4-velocity vector field from null' is treated as a perturbation. In contrast
with the null dust approximation, our approximation scheme can describe the
generation of gravitational waves in the course of the cylindrically symmetric
dust collapse.Comment: 15 page
On isotropic cylindrically symmetric stellar models
We attempt to match the most general cylindrically symmetric vacuum
space-time with a Robertson-Walker interior. The matching conditions show that
the interior must be dust filled and that the boundary must be comoving.
Further, we show that the vacuum region must be polarized. Imposing the
condition that there are no trapped cylinders on an initial time slice, we can
apply a result of Thorne's and show that trapped cylinders never evolve. This
results in a simplified line element which we prove to be incompatible with the
dust interior. This result demonstrates the impossibility of the existence of
an isotropic cylindrically symmetric star (or even a star which has a
cylindrically symmetric portion). We investigate the problem from a different
perspective by looking at the expansion scalars of invariant null geodesic
congruences and, applying to the cylindrical case, the result that the product
of the signs of the expansion scalars must be continuous across the boundary.
The result may also be understood in relation to recent results about the
impossibility of the static axially symmetric analogue of the Einstein-Straus
model.Comment: 13 pages. To appear in Classical and Quantum Gravit
Quasi-local rotating black holes in higher dimension: geometry
With a help of a generalized Raychaudhuri equation non-expanding null
surfaces are studied in arbitrarily dimensional case. The definition and basic
properties of non-expanding and isolated horizons known in the literature in
the 4 and 3 dimensional cases are generalized. A local description of horizon's
geometry is provided. The Zeroth Law of black hole thermodynamics is derived.
The constraints have a similar structure to that of the 4 dimensional spacetime
case. The geometry of a vacuum isolated horizon is determined by the induced
metric and the rotation 1-form potential, local generalizations of the area and
the angular momentum typically used in the stationary black hole solutions
case.Comment: 32 pages, RevTex
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