53 research outputs found
Determining the population properties of spinning black holes
There are at least two formation scenarios consistent with the first
gravitational-wave observations of binary black hole mergers. In field models,
black hole binaries are formed from stellar binaries that may undergo common
envelope evolution. In dynamic models, black hole binaries are formed through
capture events in globular clusters. Both classes of models are subject to
significant theoretical uncertainties. Nonetheless, the conventional wisdom
holds that the distribution of spin orientations of dynamically merging black
holes is nearly isotropic while field-model black holes prefer to spin in
alignment with the orbital angular momentum. We present a framework in which
observations of black hole mergers can be used to measure ensemble properties
of black hole spin such as the typical black hole spin misalignment. We show
how to obtain constraints on population hyperparameters using minimal
assumptions so that the results are not strongly dependent on the uncertain
physics of formation models. These data-driven constraints will facilitate
tests of theoretical models and help determine the formation history of binary
black holes using information encoded in their observed spins. We demonstrate
that the ensemble properties of binary detections can be used to search for and
characterize the properties of two distinct populations of black hole mergers.Comment: 10 pages, 5 figures, 1 table. Minor revisions, published in PR
Growing Pains: Understanding the Impact of Likelihood Uncertainty on Hierarchical Bayesian Inference for Gravitational-Wave Astronomy
Observations of gravitational waves emitted by merging compact binaries have
provided tantalising hints about stellar astrophysics, cosmology, and
fundamental physics. However, the physical parameters describing the systems,
(mass, spin, distance) used to extract these inferences about the Universe are
subject to large uncertainties. The current method of performing these analyses
requires performing many Monte Carlo integrals to marginalise over the
uncertainty in the properties of the individual binaries and the survey
selection bias. These Monte Carlo integrals are subject to fundamental
statistical uncertainties. Previous treatments of this statistical uncertainty
has focused on ensuring the precision of the inferred inference is unaffected,
however, these works have neglected the question of whether sufficient accuracy
can also be achieved. In this work, we provide a practical exploration of the
impact of uncertainty in our analyses and provide a suggested framework for
verifying that astrophysical inferences made with the gravitational-wave
transient catalogue are accurate. Applying our framework to models used by the
LIGO-Virgo-Kagra collaboration, we find that Monte Carlo uncertainty in
estimating the survey selection bias is the limiting factor in our ability to
probe narrow populations model and this will rapidly grow more problematic as
the size of the observed population increases.Comment: 8 pages, 6 figure
Gravitational-wave astronomy with an uncertain noise power spectral density
In order to extract information about the properties of compact binaries, we
must estimate the noise power spectral density of gravitational-wave data,
which depends on the properties of the gravitational-wave detector. In
practice, it is not possible to know this perfectly, only to estimate it from
the data. Multiple estimation methods are commonly used and each has a
corresponding statistical uncertainty. However, this uncertainty is widely
ignored when measuring the physical parameters describing compact binary
coalescences, and the appropriate likelihoods which account for the uncertainty
are not well known. In order to perform increasingly precise astrophysical
inference and model selection, it will be essential to account for this
uncertainty. In this work, we derive the correct likelihood for one of the most
widely used estimation methods in gravitational-wave transient analysis, the
median average. We demonstrate that simulated Gaussian noise follows the
predicted distributions. We then examine real gravitational-wave data at and
around the time of GW151012, a relatively low-significance binary black hole
merger event. We show that the data are well described by stationary-Gaussian
noise and explore the impact of different noise power spectral density
estimation methods on the astrophysical inferences we draw about GW151012.Comment: 12 pages, 7 figure
Parallelized Inference for Gravitational-Wave Astronomy
Bayesian inference is the workhorse of gravitational-wave astronomy, for
example, determining the mass and spins of merging black holes, revealing the
neutron star equation of state, and unveiling the population properties of
compact binaries. The science enabled by these inferences comes with a
computational cost that can limit the questions we are able to answer. This
cost is expected to grow. As detectors improve, the detection rate will go up,
allowing less time to analyze each event. Improvement in low-frequency
sensitivity will yield longer signals, increasing the number of computations
per event. The growing number of entries in the transient catalog will drive up
the cost of population studies. While Bayesian inference calculations are not
entirely parallelizable, key components are embarrassingly parallel:
calculating the gravitational waveform and evaluating the likelihood function.
Graphical processor units (GPUs) are adept at such parallel calculations. We
report on progress porting gravitational-wave inference calculations to GPUs.
Using a single code - which takes advantage of GPU architecture if it is
available - we compare computation times using modern GPUs (NVIDIA P100) and
CPUs (Intel Gold 6140). We demonstrate speed-ups of for
compact binary coalescence gravitational waveform generation and likelihood
evaluation and more than for population inference within the
lifetime of current detectors. Further improvement is likely with continued
development. Our python-based code is publicly available and can be used
without familiarity with the parallel computing platform, CUDA.Comment: 5 pages, 4 figures, submitted to PRD, code can be found at
https://github.com/ColmTalbot/gwpopulation
https://github.com/ColmTalbot/GPUCBC
https://github.com/ADACS-Australia/ADACS-SS18A-RSmith Add demonstration of
improvement in BNS spi
Gravitational-wave astronomy with an uncertain noise power spectral density
In order to extract information about the properties of compact binaries, we must estimate the noise power spectral density of gravitational-wave data, which depends on the properties of the gravitational-wave detector. In practice, it is not possible to know this perfectly, only to estimate it from the data. Multiple estimation methods are commonly used, and each has a corresponding statistical uncertainty. However, this uncertainty is widely ignored when measuring the physical parameters describing compact binary coalescences, and the appropriate likelihoods which account for the uncertainty are not well known. In order to perform increasingly precise astrophysical inference and model selection, it will be essential to account for this uncertainty. In this work, we derive the correct likelihood for one of the most widely used estimation methods in gravitational-wave transient analysis, the median average. We demonstrate that simulated Gaussian noise follows the predicted distributions. We then examine real gravitational-wave data at and around the time of GW151012, a relatively low-significance binary black hole merger event. We find that the difference in our inference when using different PSD estimation techniques is larger than the predicted statistical uncertainty
Searching for structure in the binary black hole spin distribution
The spins of black holes in merging binaries can reveal information related
to the formation and evolution of these systems through their gravitational
wave emission. Combining events to infer the astrophysical distribution of
black hole spins allows us to determine the relative contribution from
different formation scenarios to the population. Many previous works have
modeled spin population distributions using parametric models. While these are
valuable approaches when the observed population is small, they make strong
assumptions about the shape of the underlying distribution and are highly
susceptible to biases due to mismodeling. The results obtained with such
parametric models are only valid if the allowed shape of the distribution is
well-motivated (i.e. for astrophysical reasons). In this work, we relax these
prior assumptions and model the spin distributions using a more data-driven
approach, modeling these distributions with flexible cubic spline interpolants
in order to allow for capturing structures that the parametric models cannot.
We find that adding this flexibility to the model substantially increases the
uncertainty in the inferred distributions, but find a general trend for lower
support at high spin magnitude and a spin tilt distribution consistent with
isotropic orientations. We infer that 62 - 87% of black holes have spin
magnitudes less than a = 0.5, and 27- 50% of black holes exhibit negative
. Using the inferred distribution, we place a
conservative upper limit of 37% for the contribution of hierarchical mergers to
the astrophysical BBH population. Additionally, we find that artifacts from
unconverged Monte Carlo integrals in the likelihood can manifest as spurious
peaks and structures in inferred distributions, mandating the use of a
sufficient number of samples when using Monte Carlo integration for population
inference.Comment: 15 pages, 14 figure
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