291 research outputs found
Collapsing regions and black hole formation
Up to a conjecture in Riemannian geometry, we significantly strengthen a
recent theorem of Eardley by proving that a compact region in an initial data
surface that is collapsing sufficiently fast in comparison to its
surface-to-volume ratio must contain a future trapped region. In addition to
establishing this stronger result, the geometrical argument used does not
require any asymptotic or energy conditions on the initial data. It follows
that if such a region can be found in an asymptotically flat Cauchy surface of
a spacetime satisfying the null-convergence condition, the spacetime must
contain a black hole with the future trapped region therein. Further, up to
another conjecture, we prove a strengthened version of our theorem by arguing
that if a certain function (defined on the collection of compact subsets of the
initial data surface that are themselves three-dimensional manifolds with
boundary) is not strictly positive, then the initial data surface must contain
a future trapped region. As a byproduct of this work, we offer a slightly
generalized notion of a future trapped region as well as a new proof that
future trapped regions lie within the black hole region.Comment: 11 pages, REVTeX 3.
Coyote, Canis latrans, Predation on a Bison, Bison bison, Calf in Yellowstone National Park
We observed a single adult male Coyote (Canis latrans) kill a Bison (Bison bison) calf in Yellowstone National Park. The predation is, to our knowledge, the only direct and complete observation of a lone Coyote capturing and killing a Bison calf. The bison calf had unsuccessfully attempted to ford a river with a group and subsequently become stranded alone in the territory of a six-year-old alpha male Coyote
Observation of direct hadronic pairs in nucleus-nucleus collisions in JACEE emulsion chambers
In a number of high energy ( or = 1 TeV/amu) nucleus-nucleus collisions observed in Japanese-American Cooperative Emulsion Experiment (JACEE) emulsion chambers, nonrandom spatial association of produced charged particles, mostly hadronic pairs, are observed. Similar narrow pairs are observed in about 100 events at much low energy (20 to 60 GeV/amu). Analysis shows that 30 to 50% of Pair abundances are understood by the Hambury-Brown-Twiss effect, and the remainder seems to require other explanations
Excessive production of electron pairs by soft photons in low multiplicity ion interactions
Three multiply charged primary cosmic ray interactions with carbon nuclei are reported, in which the number of materialized electron pairs within a distance of about 0.3 conversion length is larger than predicted from isospin considerations. These are the most energetic (sigma E gamma 4 TeV) of the low multiplicity ( 15 tracks) events observed in the Japanese-American Cooperative Experiment (JACEE-2) emulsion chamber
Nucleus-nucleus interaction above several hundred GeV/n
The Japanese-American Cooperative Emulsion Experiment (JACEE) have been investigating high energy nuclear interactions of cosmic ray nuclei by means of balloon-borne emulsion chamber. Current exposure parameters are listed. Analysis of the last two experiments (JACEE4 and JACEE5) are still in progress. A result of semi-inclusive analysis of a sample set of central collision events is presented here, concerning multiplicity, rapidity fluctuation for extremely high multiplicity events and correlation between transverse momentum and estimated energy density
Heavy nucleus collisions between 20 and 60 GeV/nucleon
Interest in studying relativistic nucleus-nucleus interations arises from the fact that they offer an opportunity to probe nuclear matter at high density and temperature. It is expected that under such extreme conditions a transition from hadronic matter into quark-gluon plasma occurs and that in the interactions of highly relativistic nuclei such conditions are created. Cosmic rays remain a unique source of high energy heavy nuclei. The Japanese-American Cooperative Emulsion Experiment (JACEE-3) was designed to study the collisions of heavy cosmic ray nuclei with different nuclear targets at energies beyond 20 GeV/nucleon. JACEE-3 experiment was carried out using a combined electronic counters and an emulsion chamber detector, which was exposed to the cosmic rays on a balloon at an altitude of 5 g/sq cm
Nucleon-nucleus interactions from JACEE
Results on hadron-nucleus interactions from the Japanese-American Cooperation Emulsion Experiment experiment are presented. Angular distributions for charged particles, and angular and transverse momentum spectra for photons have been measured for a sample of events with sigma epsilon sub gamma. Results on central rapidity density and transverse energy flow are discussed
Just how long can you live in a black hole and what can be done about it?
We study the problem of how long a journey within a black hole can last.
Based on our observations, we make two conjectures. First, for observers that
have entered a black hole from an asymptotic region, we conjecture that the
length of their journey within is bounded by a multiple of the future
asymptotic ``size'' of the black hole, provided the spacetime is globally
hyperbolic and satisfies the dominant-energy and non-negative-pressures
conditions. Second, for spacetimes with Cauchy surfaces (or an
appropriate generalization thereof) and satisfying the dominant energy and
non-negative-pressures conditions, we conjecture that the length of a journey
anywhere within a black hole is again bounded, although here the bound requires
a knowledge of the initial data for the gravitational field on a Cauchy
surface. We prove these conjectures in the spherically symmetric case. We also
prove that there is an upper bound on the lifetimes of observers lying ``deep
within'' a black hole, provided the spacetime satisfies the
timelike-convergence condition and possesses a maximal Cauchy surface. Further,
we investigate whether one can increase the lifetime of an observer that has
entered a black hole, e.g., by throwing additional matter into the hole.
Lastly, in an appendix, we prove that the surface area of the event horizon
of a black hole in a spherically symmetric spacetime with ADM mass
is always bounded by , provided
that future null infinity is complete and the spacetime is globally hyperbolic
and satisfies the dominant-energy condition.Comment: 20 pages, REVTeX 3.0, 6 figures included, self-unpackin
Lifetimes of spherically symmetric closed universes
It is proven that any spherically symmetric spacetime that possesses a
compact Cauchy surface and that satisfies the dominant-energy and
non-negative-pressures conditions must have a finite lifetime in the sense that
all timelike curves in such a spacetime must have a length no greater than , where is the mass associated with the spheres of
symmetry. This result gives a complete resolution, in the spherically symmetric
case, of one version of the closed-universe recollapse conjecture (though it is
likely that a slightly better bound can be established). This bound has the
desirable properties of being computable from the (spherically symmetric)
initial data for the spacetime and having a very simple form. In fact, its form
is the same as was established, using a different method, for the spherically
symmetric massless scalar field spacetimes, thereby proving a conjecture
offered in that work. Prospects for generalizing these results beyond the
spherically symmetric case are discussed.Comment: 12 pages (uuencoded postscript; self-unpacking), NCSU-MP-940
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