5,857 research outputs found
"Are Black Holes in Brans-Dicke Theory precisely the same as in General Relativity?"
We study a three-parameters family of solutions of the Brans-Dicke field
equations. They are static and spherically symmetric. We find the range of
parameters for which this solution represents a black hole different from the
Schwarzschild one. We find a subfamily of solutions which agrees with
experiments and observations in the solar system. We discuss some astrophysical
applications and the consequences on the "no hair" theorems for black holes.Comment: 13pages, Plain Te
Making use of geometrical invariants in black hole collisions
We consider curvature invariants in the context of black hole collision
simulations. In particular, we propose a simple and elegant combination of the
Weyl invariants I and J, the {\sl speciality index} . In the context
of black hole perturbations provides a measure of the size of the
distortions from an ideal Kerr black hole spacetime. Explicit calculations in
well-known examples of axisymmetric black hole collisions demonstrate that this
quantity may serve as a useful tool for predicting in which cases perturbative
dynamics provide an accurate estimate of the radiation waveform and energy.
This makes particularly suited to studying the transition from
nonlinear to linear dynamics and for invariant interpretation of numerical
results.Comment: 4 pages, 3 eps figures, Revte
Spin-orbit interactions in black-hole binaries
We perform numerical simulations of black-hole binaries to study the exchange
of spin and orbital angular momentum during the last, highly nonlinear, stages
of the coalescence process. To calculate the transfer of angular momentum from
orbital to spin, we start with two quasi-circular configurations, one with
initially non-spinning black holes, the other with corotating black holes. In
both cases the binaries complete almost two orbits before merging. We find
that, during these last orbits, the specific spin (a/m) of each horizon
increases by only 0.012 for the initially non-spinning configuration, and by
only 0.006 for the initially corotating configuration. By contrast, the
corotation value for the specific spin should increase from 0.1 at the initial
proper separation of 10M to 0.33 when the proper separation is 5M. Thus the
spin-orbit coupling is far too weak to tidally lock the binary to a corotating
state during the late-inspiral phase. We also study the converse transfer from
spin into orbital motion. In this case, we start the simulations with parallel,
highly-spinning non-boosted black holes. As the collision proceeds, the system
acquires a non-head-on orbital motion, due to spin-orbit coupling, that leads
to the radiation of angular momentum. We are able to accurately measure the
energy and angular momentum losses and model their dependence on the initial
spins.Comment: This version corrects two typos in Eq (4) and Table I present in the
published versio
Perturbative effects of spinning black holes with applications to recoil velocities
Recently, we proposed an enhancement of the Regge-Wheeler-Zerilli formalism
for first-order perturbations about a Schwarzschild background that includes
first-order corrections due to the background black-hole spin. Using this
formalism, we investigate gravitational wave recoil effects from a spinning
black-hole binary system analytically. This allows us to better understand the
origin of the large recoils observed in full numerical simulation of spinning
black hole binaries.Comment: Proceedings of Theory Meets Data Analysis at Comparable and Extreme
Mass Ratios (NRDA/Capra 2010), Perimeter Institute, June 2010 - 12 page
The last orbit of binary black holes
We have used our new technique for fully numerical evolutions of orbiting
black-hole binaries without excision to model the last orbit and merger of an
equal-mass black-hole system. We track the trajectories of the individual
apparent horizons and find that the binary completed approximately one and a
third orbits before forming a common horizon. Upon calculating the complete
gravitational radiation waveform, horizon mass, and spin, we find that the
binary radiated 3.2% of its mass and 24% of its angular momentum. The early
part of the waveform, after a relatively short initial burst of spurious
radiation, is oscillatory with increasing amplitude and frequency, as expected
from orbital motion. The waveform then transitions to a typical `plunge'
waveform; i.e. a rapid rise in amplitude followed by quasinormal ringing. The
plunge part of the waveform is remarkably similar to the waveform from the
previously studied `ISCO' configuration. We anticipate that the plunge
waveform, when starting from quasicircular orbits, has a generic shape that is
essentially independent of the initial separation of the binary.Comment: 5 pages, 5 figures, revtex
A perturbative solution for gravitational waves in quadratic gravity
We find a gravitational wave solution to the linearized version of quadratic
gravity by adding successive perturbations to the Einstein's linearized field
equations. We show that only the Ricci squared quadratic invariant contributes
to give a different solution of those found in Einstein's general relativity.
The perturbative solution is written as a power series in the
parameter, the coefficient of the Ricci squared term in the quadratic
gravitational action. We also show that, for monochromatic waves of a given
angular frequency , the perturbative solution can be summed out to give
an exact solution to linearized version of quadratic gravity, for
.
This result may lead to implications to the predictions for gravitational
wave backgrounds of cosmological origin.Comment: 9 pages, to appear in CQ
Approximate black hole binary spacetime via asymptotic matching
We construct a fully analytic, general relativistic, nonspinning black hole
binary spacetime that approximately solves the vacuum Einstein equations
everywhere in space and time for black holes sufficiently well separated. The
metric is constructed by asymptotically matching perturbed Schwarzschild
metrics near each black hole to a two-body post-Newtonian metric far from them,
and a two-body post-Minkowskian metric farther still. Asymptotic matching is
done without linearizing about a particular time slice, and thus it is valid
dynamically and for all times, provided the binary is sufficiently well
separated. This approximate global metric can be used for long dynamical
evolutions of relativistic magnetohydrodynamical, circumbinary disks around
inspiraling supermassive black holes to study a variety of phenomena.Comment: 17 pages, 8 figures, 1 table. Appendix added to match published
versio
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