125 research outputs found
Anatomy of the binary black hole recoil: A multipolar analysis
We present a multipolar analysis of the gravitational recoil computed in
recent numerical simulations of binary black hole (BH) coalescence, for both
unequal masses and non-zero, non-precessing spins. We show that multipole
moments up to and including l=4 are sufficient to accurately reproduce the
final recoil velocity (within ~2%) and that only a few dominant modes
contribute significantly to it (within ~5%). We describe how the relative
amplitudes, and more importantly, the relative phases, of these few modes
control the way in which the recoil builds up throughout the inspiral, merger,
and ringdown phases. We also find that the numerical results can be reproduced
by an ``effective Newtonian'' formula for the multipole moments obtained by
replacing the radial separation in the Newtonian formulae with an effective
radius computed from the numerical data. Beyond the merger, the numerical
results are reproduced by a superposition of three Kerr quasi-normal modes
(QNMs). Analytic formulae, obtained by expressing the multipole moments in
terms of the fundamental QNMs of a Kerr BH, are able to explain the onset and
amount of ``anti-kick'' for each of the simulations. Lastly, we apply this
multipolar analysis to help explain the remarkable difference between the
amplitudes of planar and non-planar kicks for equal-mass spinning black holes.Comment: 28 pages, 20 figures, submitted to PRD; v2: minor revisions from
referee repor
Modeling kicks from the merger of generic black-hole binaries
Recent numerical relativistic results demonstrate that the merger of
comparable-mass spinning black holes has a maximum ``recoil kick'' of up to
\sim 4000 \kms. However the scaling of these recoil velocities with mass
ratio is poorly understood. We present new runs showing that the maximum
possible kick perpendicular to the orbital plane does not scale as
(where is the symmetric mass ratio), as previously proposed, but is more
consistent with , at least for systems with low orbital precession.
We discuss the effect of this dependence on galactic ejection scenarios and
retention of intermediate-mass black holes in globular clusters.Comment: 5 pages, 1 figure, 3 tables. Version published in Astrophys. J. Let
Observing Mergers of Non-Spinning Black-Hole Binaries
Advances in the field of numerical relativity now make it possible to calculate the final, most powerful merger phase of binary black-hole coalescence for generic binaries. The state of the art has advanced well beyond the equal-mass case into the unequal-mass and spinning regions of parameter space. We present a study of the nonspinning portion of parameter space, primarily using an analytic waveform model tuned to available numerical data, with an emphasis on observational implications. We investigate the impact of varied m8BS ratio on merger signal-to-noise ratios (SNR~) for several detectors, and compare our results with expectations from the test-mass limit. We note a striking similarity of the waveform phasing of the merger waveform across the available mass ratios. Motivated by this, we calculate the match between our equal-mass and 4:1 mass-ratio waveforms during the merger as a function of location on the source sky, using a new formalism for the match that accounts for higher harmonics. This is an indicator of the amount of degeneracy in mass ratio for mergers of moderate mass ratio systems
A General Formula for Black Hole Gravitational Wave Kicks
Although the gravitational wave kick velocity in the orbital plane of
coalescing black holes has been understood for some time, apparently
conflicting formulae have been proposed for the dominant out-of-plane kick,
each a good fit to different data sets. This is important to resolve because it
is only the out-of-plane kicks that can reach more than 500 km/s and can thus
eject merged remnants from galaxies. Using a different ansatz for the
out-of-plane kick, we show that we can fit almost all existing data to better
than 5 %. This is good enough for any astrophysical calculation, and shows that
the previous apparent conflict was only because the two data sets explored
different aspects of the kick parameter space.Comment: 14 pages
Recoiling from a Kick in the Head-On Case
Recoil "kicks" induced by gravitational radiation are expected in the inspiral and merger of black holes. Recently the numerical relativity community has begun to measure the significant kicks found when both unequal masses and spins are considered. Because understanding the cause and magnitude of each component of this kick may be complicated in inspiral simulations, we consider these effects in the context of a simple test problem. We study recoils from collisions of binaries with initially head-on trajectories, starting with the simplest case of equal masses with no spin; adding spin and varying the mass ratio, both separately and jointly. We find spin-induced recoils to be significant even in head-on configurations. Additionally, it appears that the scaling of transverse kicks with spins is consistent with post-Newtonian (PN) theory, even though the kick is generated in the nonlinear merger interaction, where PN theory should not apply. This suggests that a simple heuristic description might be effective in the estimation of spin-kicks
Mergers of nonspinning black-hole binaries: Gravitational radiation characteristics
We present a detailed descriptive analysis of the gravitational radiation
from black-hole binary mergers of nonspinning black holes, based on numerical
simulations of systems varying from equal-mass to a 6:1 mass ratio. Our primary
goal is to present relatively complete information about the waveforms,
including all the leading multipolar components, to interested researchers. In
our analysis, we pursue the simplest physical description of the dominant
features in the radiation, providing an interpretation of the waveforms in
terms of an {\em implicit rotating source}. This interpretation applies
uniformly to the full wave train, from inspiral through ringdown. We emphasize
strong relationships among the modes that persist through the full
wave train. Exploring the structure of the waveforms in more detail, we conduct
detailed analytic fitting of the late-time frequency evolution, identifying a
key quantitative feature shared by the modes among all mass ratios. We
identify relationships, with a simple interpretation in terms of the implicit
rotating source, among the evolution of frequency and amplitude, which hold for
the late-time radiation. These detailed relationships provide sufficient
information about the late-time radiation to yield a predictive model for the
late-time waveforms, an alternative to the common practice of modeling by a sum
of quasinormal mode overtones. We demonstrate an application of this in a new
effective-one-body-based analytic waveform model.Comment: 25 pages, 21 figures, 5 tables; published version, with added
reference
Recoiling from a kick in the head-on collision of spinning black holes
Recoil ``kicks'' induced by gravitational radiation are expected in the
inspiral and merger of black holes. Recently the numerical relativity community
has begun to measure the significant kicks found when both unequal masses and
spins are considered. Because understanding the cause and magnitude of each
component of this kick may be complicated in inspiral simulations, we consider
these effects in the context of a simple test problem. We study recoils from
collisions of binaries with initially head-on trajectories, starting with the
simplest case of equal masses with no spin and then adding spin and varying the
mass ratio, both separately and jointly. We find spin-induced recoils to be
significant relative to unequal-mass recoils even in head-on configurations.
Additionally, it appears that the scaling of transverse kicks with spins is
consistent with post-Newtonian theory, even though the kick is generated in the
nonlinear merger interaction, where post-Newtonian theory should not apply.
This suggests that a simple heuristic description might be effective in the
estimation of spin-kicks.Comment: 12 pages, 10 figures. Replaced with published version, including more
discussion of convergence and properties of final hol
Spatially Resolving a Starburst Galaxy at Hard X-ray Energies: NuSTAR, Chandra, AND VLBA Observations of NGC 253
Prior to the launch of NuSTAR, it was not feasible to spatially resolve the
hard (E > 10 keV) emission from galaxies beyond the Local Group. The combined
NuSTAR dataset, comprised of three ~165 ks observations, allows spatial
characterization of the hard X-ray emission in the galaxy NGC 253 for the first
time. As a follow up to our initial study of its nuclear region, we present the
first results concerning the full galaxy from simultaneous NuSTAR, Chandra, and
VLBA monitoring of the local starburst galaxy NGC 253. Above ~10 keV, nearly
all the emission is concentrated within 100" of the galactic center, produced
almost exclusively by three nuclear sources, an off-nuclear ultraluminous X-ray
source (ULX), and a pulsar candidate that we identify for the first time in
these observations. We detect 21 distinct sources in energy bands up to 25 keV,
mostly consisting of intermediate state black hole X-ray binaries. The global
X-ray emission of the galaxy - dominated by the off-nuclear ULX and nuclear
sources, which are also likely ULXs - falls steeply (photon index >~ 3) above
10 keV, consistent with other NuSTAR-observed ULXs, and no significant excess
above the background is detected at E > 40 keV. We report upper limits on
diffuse inverse Compton emission for a range of spatial models. For the most
extended morphologies considered, these hard X-ray constraints disfavor a
dominant inverse Compton component to explain the {\gamma}-ray emission
detected with Fermi and H.E.S.S. If NGC 253 is typical of starburst galaxies at
higher redshift, their contribution to the E > 10 keV cosmic X-ray background
is < 1%.Comment: 20 pages, 14 figures, accepted for publication in Ap
Modeling kicks from the merger of generic black-hole binaries
Recent numerical relativistic results demonstrate that the merger of
comparable-mass spinning black holes has a maximum ``recoil kick'' of up to
\sim 4000 \kms. However the scaling of these recoil velocities with mass
ratio is poorly understood. We present new runs showing that the maximum
possible kick perpendicular to the orbital plane does not scale as
(where is the symmetric mass ratio), as previously proposed, but is more
consistent with , at least for systems with low orbital precession.
We discuss the effect of this dependence on galactic ejection scenarios and
retention of intermediate-mass black holes in globular clusters.Comment: 5 pages, 1 figure, 3 tables. Version published in Astrophys. J. Let
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