618 research outputs found
Infall of a particle into a black hole as a model for gravitational radiation from the galactic center
I present here the results of the study of the gravitational radiation
generated by the infall (from rest at radius ) of a point particle of mass
into a Schwarzschild black hole of mass . We use Laplace's transform
methods and find that the spectra of radiation for presents
a series of evenly spaced bumps. The total radiated energy is not monotonically
decreasing with , but presents a joroba (hunch-back) at around
. I finally discuss the detectability of the gravitational
radiation coming from the black hole in the center of our galaxy.Comment: Latex, 4 pages, 3 figures (resume' of the talk at the 18th Texas
Symposium
Some Thermodynamic Aspects of Black Holes and Singularities
We review and correct the classical critical exponents characterizing the
transition from negative to positive black hole's heat capacity at high
charge--angular momentum. We discuss the stability properties of black holes as
a thermodynamic system in equilibrium with a radiation bath (canonical
ensamble) by using the Helmholtz free energy potential. We finally analytically
extend the analysis to negative mass holes and study its thermodynamical
stability behavior.Comment: 16 pages, RevTeX, 5 compressed figure
Perturbative evolution of nonlinear initial data for binary black holes: Zerilli vs. Teukolsky
We consider the problem of evolving nonlinear initial data in the close limit
regime. Metric and curvature perturbations of nonrotating black holes are
equivalent to first perturbative order, but Moncrief waveform in the former
case and Weyl scalar in the later differ when nonlinearities are
present. For exact Misner initial data (two equal mass black holes initially at
rest), metric perturbations evolved via the Zerilli equation suffer of a
premature break down (at proper separation of the holes ) while
the exact Weyl scalar evolved via the Teukolsky equation keeps a very
good agreement with full numerical results up to . We argue that
this inequivalent behavior holds for a wider class of conformally flat initial
data than those studied here. We then discuss the relevance of these results
for second order perturbative computations and for perturbations to take over
full numerical evolutions of Einstein equations.Comment: 7 pages, 7 figure
A time-domain fourth-order-convergent numerical algorithm to integrate black hole perturbations in the extreme-mass-ratio limit
We obtain a fourth order accurate numerical algorithm to integrate the
Zerilli and Regge-Wheeler wave equations, describing perturbations of
nonrotating black holes, with source terms due to an orbiting particle. Those
source terms contain the Dirac's delta and its first derivative. We also
re-derive the source of the Zerilli and Regge-Wheeler equations for more
convenient definitions of the waveforms, that allow direct metric
reconstruction (in the Regge-Wheeler gauge).Comment: 30 pages, 12 figure
"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
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
Pragmatic approach to gravitational radiation reaction in binary black holes
We study the relativistic orbit of binary black holes in systems with small
mass ratio. The trajectory of the smaller object (another black hole or a
neutron star), represented as a particle, is determined by the geodesic
equation on the perturbed massive black hole spacetime. The particle itself
generates the gravitational perturbations leading to a problem that needs
regularization. Here we study perturbations around a Schwarzschild black hole
using Moncrief's gauge invariant formalism. We decompose the perturbations into
multipoles to show that all metric coefficients are at the
location of the particle. Summing over , to reconstruct the full metric,
gives a formally divergent result. We succeed in bringing this sum to a
generalized Riemann's function regularization scheme and show that this
is tantamount to subtract the piece to each multipole. We
explicitly carry out this regularization and numerically compute the first
order geodesics. Application of this method to general orbits around rotating
black holes would generate accurate templates for gravitational wave laser
interferometric detectors.Comment: 5 pages, 2 figures, improved text and figures. To appear in PR
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