90 research outputs found
Improving Pulsar Timing through Interstellar Scatter Correction
Though pulsar timing has confirmed the existence of gravitational waves, no technique has directly detected them. Jenet et al. state the requirements for the Parkes Pulsar Timing Array (PPTA) to make a significant detection of the stochastic gravitational wave background within five years. By employing the scintillation information in observations for each pulsar at every epoch, I believe interstellar scattering, an underestimated source of timing noise, can be corrected enough for the PPTA to meet these requirements. The improved detection threshold will help answer important questions about black hole mergers, galaxy evolution, and gravitation
Improving Pulsar Timing through Interstellar Scatter Correction
Though pulsar timing has confirmed the existence of gravitational waves, no technique has directly detected them. Jenet et al. state the requirements for the Parkes Pulsar Timing Array (PPTA) to make a significant detection of the stochastic gravitational wave background within five years. By employing the scintillation information in observations for each pulsar at every epoch, I believe interstellar scattering, an underestimated source of timing noise, can be corrected enough for the PPTA to meet these requirements. The improved detection threshold will help answer important questions about black hole mergers, galaxy evolution, and gravitation
A Surrogate Model of Gravitational Waveforms from Numerical Relativity Simulations of Precessing Binary Black Hole Mergers
We present the first surrogate model for gravitational waveforms from the
coalescence of precessing binary black holes. We call this surrogate model
NRSur4d2s. Our methodology significantly extends recently introduced
reduced-order and surrogate modeling techniques, and is capable of directly
modeling numerical relativity waveforms without introducing phenomenological
assumptions or approximations to general relativity. Motivated by GW150914,
LIGO's first detection of gravitational waves from merging black holes, the
model is built from a set of numerical relativity (NR) simulations with
mass ratios , dimensionless spin magnitudes up to , and the
restriction that the initial spin of the smaller black hole lies along the axis
of orbital angular momentum. It produces waveforms which begin
gravitational wave cycles before merger and continue through ringdown, and
which contain the effects of precession as well as all
spin-weighted spherical-harmonic modes. We perform cross-validation studies to
compare the model to NR waveforms \emph{not} used to build the model, and find
a better agreement within the parameter range of the model than other,
state-of-the-art precessing waveform models, with typical mismatches of
. We also construct a frequency domain surrogate model (called
NRSur4d2s_FDROM) which can be evaluated in and is suitable
for performing parameter estimation studies on gravitational wave detections
similar to GW150914.Comment: 34 pages, 26 figure
Fast and accurate prediction of numerical relativity waveforms from binary black hole coalescences using surrogate models
Simulating a binary black hole (BBH) coalescence by solving Einstein's
equations is computationally expensive, requiring days to months of
supercomputing time. Using reduced order modeling techniques, we construct an
accurate surrogate model, which is evaluated in a millisecond to a second, for
numerical relativity (NR) waveforms from non-spinning BBH coalescences with
mass ratios in and durations corresponding to about orbits
before merger. We assess the model's uncertainty and show that our modeling
strategy predicts NR waveforms {\em not} used for the surrogate's training with
errors nearly as small as the numerical error of the NR code. Our model
includes all spherical-harmonic waveform modes resolved by
the NR code up to We compare our surrogate model to Effective One
Body waveforms from - for advanced LIGO detectors and find
that the surrogate is always more faithful (by at least an order of magnitude
in most cases).Comment: Updated to published version, which includes a section comparing the
surrogate and effective-one-body models. The surrogate is publicly available
for download at http://www.black-holes.org/surrogates/ . 6 pages, 6 figure
Improved methods for simulating nearly extremal binary black holes
Astrophysical black holes could be nearly extremal (that is, rotating nearly
as fast as possible); therefore, nearly extremal black holes could be among the
binaries that current and future gravitational-wave observatories will detect.
Predicting the gravitational waves emitted by merging black holes requires
numerical-relativity simulations, but these simulations are especially
challenging when one or both holes have mass and spin exceeding the
Bowen-York limit of . We present improved methods that enable us to
simulate merging, nearly extremal black holes more robustly and more
efficiently. We use these methods to simulate an unequal-mass, precessing
binary black hole coalescence, where the larger black hole has . We
also use these methods to simulate a non-precessing binary black hole
coalescence, where both black holes have , nearly reaching the
Novikov-Thorne upper bound for holes spun up by thin accretion disks. We
demonstrate numerical convergence and estimate the numerical errors of the
waveforms; we compare numerical waveforms from our simulations with
post-Newtonian and effective-one-body waveforms; we compare the evolution of
the black-hole masses and spins with analytic predictions; and we explore the
effect of increasing spin magnitude on the orbital dynamics (the so-called
"orbital hangup" effect).Comment: 18 pages, 18 figure
Accuracy of binary black hole waveform models for aligned-spin binaries
Coalescing binary black holes are among the primary science targets for
second generation ground-based gravitational wave (GW) detectors. Reliable GW
models are central to detection of such systems and subsequent parameter
estimation. This paper performs a comprehensive analysis of the accuracy of
recent waveform models for binary black holes with aligned spins, utilizing a
new set of high-accuracy numerical relativity simulations. Our analysis
covers comparable mass binaries (), and samples
independently both black hole spins up to dimensionless spin-magnitude of
for equal-mass binaries and for unequal mass binaries. Furthermore, we
focus on the high-mass regime (total mass ). The two most
recent waveform models considered (PhenomD and SEOBNRv2) both perform very well
for signal detection, losing less than 0.5\% of the recoverable signal-to-noise
ratio , except that SEOBNRv2's efficiency drops mildly for both black
hole spins aligned with large magnitude. For parameter estimation, modeling
inaccuracies of SEOBNRv2 are found to be smaller than systematic uncertainties
for moderately strong GW events up to roughly . PhenomD's
modeling errors are found to be smaller than SEOBNRv2's, and are generally
irrelevant for . Both models' accuracy deteriorates with
increased mass-ratio, and when at least one black hole spin is large and
aligned. The SEOBNRv2 model shows a pronounced disagreement with the numerical
relativity simulation in the merger phase, for unequal masses and
simultaneously both black hole spins very large and aligned. Two older waveform
models (PhenomC and SEOBNRv1) are found to be distinctly less accurate than the
more recent PhenomD and SEOBNRv2 models. Finally, we quantify the bias expected
from all GW models during parameter estimation for recovery of binary's masses
and spins.Comment: 24 pages, 15 figures, minor change
On the accuracy and precision of numerical waveforms: Effect of waveform extraction methodology
We present a new set of 95 numerical relativity simulations of non-precessing
binary black holes (BBHs). The simulations sample comprehensively both
black-hole spins up to spin magnitude of 0.9, and cover mass ratios 1 to 3. The
simulations cover on average 24 inspiral orbits, plus merger and ringdown, with
low initial orbital eccentricities . A subset of the simulations
extends the coverage of non-spinning BBHs up to mass ratio .
Gravitational waveforms at asymptotic infinity are computed with two
independent techniques, extrapolation, and Cauchy characteristic extraction. An
error analysis based on noise-weighted inner products is performed. We find
that numerical truncation error, error due to gravitational wave extraction,
and errors due to the finite length of the numerical waveforms are of similar
magnitude, with gravitational wave extraction errors somewhat dominating at
noise-weighted mismatches of . This set of waveforms will
serve to validate and improve aligned-spin waveform models for gravitational
wave science.Comment: 22 pages, 9 figure
Periastron Advance in Spinning Black Hole Binaries: Gravitational Self-Force from Numerical Relativity
We study the general relativistic periastron advance in spinning black hole
binaries on quasi-circular orbits, with spins aligned or anti-aligned with the
orbital angular momentum, using numerical-relativity simulations, the
post-Newtonian approximation, and black hole perturbation theory. By imposing a
symmetry by exchange of the bodies' labels, we devise an improved version of
the perturbative result, and use it as the leading term of a new type of
expansion in powers of the symmetric mass ratio. This allows us to measure, for
the first time, the gravitational self-force effect on the periastron advance
of a non-spinning particle orbiting a Kerr black hole of mass M and spin S =
-0.5 M^2, down to separations of order 9M. Comparing the predictions of our
improved perturbative expansion with the exact results from numerical
simulations of equal-mass and equal-spin binaries, we find a remarkable
agreement over a wide range of spins and orbital separations.Comment: 18 pages, 12 figures; matches version to appear in Phys. Rev.
Modeling the source of GW150914 with targeted numerical-relativity simulations
In fall of 2015, the two LIGO detectors measured the gravitational wave
signal GW150914, which originated from a pair of merging black holes. In the
final 0.2 seconds (about 8 gravitational-wave cycles) before the amplitude
reached its maximum, the observed signal swept up in amplitude and frequency,
from 35 Hz to 150 Hz. The theoretical gravitational-wave signal for merging
black holes, as predicted by general relativity, can be computed only by full
numerical relativity, because analytic approximations fail near the time of
merger. Moreover, the nearly-equal masses, moderate spins, and small number of
orbits of GW150914 are especially straightforward and efficient to simulate
with modern numerical-relativity codes. In this paper, we report the modeling
of GW150914 with numerical-relativity simulations, using black-hole masses and
spins consistent with those inferred from LIGO's measurement. In particular, we
employ two independent numerical-relativity codes that use completely different
analytical and numerical methods to model the same merging black holes and to
compute the emitted gravitational waveform; we find excellent agreement between
the waveforms produced by the two independent codes. These results demonstrate
the validity, impact, and potential of current and future studies using
rapid-response, targeted numerical-relativity simulations for better
understanding gravitational-wave observations.Comment: 11 pages, 3 figures, submitted to Classical and Quantum Gravit
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