82 research outputs found
Positive energy theorem implies constraints on static steller models
Using the positive energy theorem, we derive some constraints on static
steller models in asymptotically flat spacetimes in a general setting without
imposing spherical symmetry. We show that there exist no regular solutions
under certain conditions on the equation of state. As the contraposition, we
obtain some constraints on the pressure and adiabatic index.Comment: 7 pages, final version accepted for publication in Prog. Theore. Phy
Distorted static photon surfaces in perturbed Reissner-Nordstr\"om spacetimes
The photon surface is defined as a timelike surface such that any photon
emitted in arbitrary tangential direction to from an arbitrary point on
continues to propagate on . In this paper, we examine whether a static
photon surface can be present in distorted electrovacuum spacetimes with
perturbative approach, by constructing analytic solutions to the equations for
static perturbations of a Reissner-Nordstr\"om spacetime that are regular
outside the background photon surface. For each of the modes, there
are two physical solutions to the perturbative equations that correspond to
adding the multipole moments of mass and electric charge, respectively. By
adjusting the ratio of the amplitudes of the two solutions appropriately, it is
possible to realize a distorted photon surface. In the case of ,
although there is only one physical solution to the perturbative equations,
there is also a degree of freedom to shift the coordinate position of the
photon surface, and this enables the formation of a photon surface. Such a
photon surface has a spherically symmetric spatial section, but it is also
distorted in the three-dimensional sense. Our results show that distorted
static photon surfaces can be formed at least at the level of the first-order
perturbations, and imply that the uniqueness of the photon surface may not hold
in electrovacuum spacetimes.Comment: 40 pages , 5 figure
Close-slow analysis for head-on collision of two black holes in higher dimensions: Bowen-York initial data
Scenarios of large extra dimensions have enhanced the importance for the
study of black holes in higher dimensions. In this paper, we analyze an
axisymmetric system of two black holes. Specifically, the Bowen-York method is
generalized for higher dimensions in order to calculate the initial data for
head-on collision of two equal-mass black holes. Then, the initial data are
evolved adopting the close-slow approximation to study gravitational waves
emitted during the collision. We derive an empirical formula for radiation
efficiency, which depends weakly on the dimensionality. Possible implications
of our results for the black hole formation in particle colliders are
discussed.Comment: 28 pages, 7 figures, published versio
On existence of matter outside a static black hole
It is expected that matter composed of a perfect fluid cannot be at rest
outside of a black hole if the spacetime is asymptotically flat and static
(non-rotating). However, there has not been a rigorous proof for this
expectation without assuming spheical symmetry. In this paper, we provide a
proof of non-existence of matter composed of a perfect fluid in static black
hole spacetimes under certain conditions, which can be interpreted as a
relation between the stellar mass and the black hole mass.Comment: 4pages, final version accepted for publication in Journal of
Mathematical Physic
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