62 research outputs found
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
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
The curious case of GW200129: interplay between spin-precession inference and data-quality issues
Measurement of spin-precession in black hole binary mergers observed with
gravitational waves is an exciting milestone as it relates to both general
relativistic dynamics and astrophysical binary formation scenarios. In this
study, we revisit the evidence for spin-precession in GW200129 and localize its
origin to data in LIGO Livingston in the 20--50\,Hz frequency range where the
signal amplitude is lower than expected from a non-precessing binary given all
the other data. These data are subject to known data quality issues as a glitch
was subtracted from the detector's strain data. The lack of evidence for
spin-precession in LIGO Hanford leads to a noticeable inconsistency between the
inferred binary mass ratio and precessing spin in the two LIGO detectors,
something not expected from solely different Gaussian noise realizations. We
revisit the LIGO Livingston glitch mitigation and show that the difference
between a spin-precessing and a non-precessing interpretation for GW200129 is
smaller than the statistical and systematic uncertainty of the glitch
subtraction, finding that the support for spin-precession depends sensitively
on the glitch modeling. We also investigate the signal-to-noise ratio
trigger in the less sensitive Virgo detector. Though not influencing the
spin-precession studies, the Virgo trigger is grossly inconsistent with the
ones in LIGO Hanford and LIGO Livingston as it points to a much heavier system.
We interpret the Virgo data in the context of further data quality issues.
While our results do not disprove the presence of spin-precession in GW200129,
we argue that any such inference is contingent upon the statistical and
systematic uncertainty of the glitch mitigation. Our study highlights the role
of data quality investigations when inferring subtle effects such as
spin-precession for short signals such as the ones produced by high-mass
systems.Comment: 17 pages, 14 figures, 2 tables. Data release:
https://zenodo.org/record/725965
Two novel/ancient myosins in mammalian skeletal muscles: MYH14/7b and MYH15 are expressed in extraocular muscles and muscle spindles
The mammalian genome contains three ancient sarcomeric myosin heavy chain (MYH) genes, MYH14/7b, MYH15 and MYH16, in addition to the two well characterized clusters of skeletal and cardiac MYHs. MYH16 is expressed in jaw muscles of carnivores; however the expression pattern of MYH14 and MYH15 is not known. MYH14 and MYH15 orthologues are present in frogs and birds, coding for chicken slow myosin 2 and ventricular MYH, respectively, whereas only MYH14 orthologues have been detected in fish. In all species the MYH14 gene contains a microRNA, miR-499. Here we report that in rat and mouse, MYH14 and miR-499 transcripts are detected in heart, slow muscles and extraocular (EO) muscles, whereas MYH15 transcripts are detected exclusively in EO muscles. However, MYH14 protein is detected only in a minor fibre population in EO muscles, corresponding to slow-tonic fibres, and in bag fibres of muscle spindles. MYH15 protein is present in most fibres of the orbital layer of EO muscles and in the extracapsular region of bag fibres. During development, MYH14 is expressed at low levels in skeletal muscles, heart and all EO muscle fibres but disappears from most fibres, except the slow-tonic fibres, after birth. In contrast, MYH15 is absent in embryonic and fetal muscles and is first detected after birth in the orbital layer of EO muscles. The identification of the expression pattern of MYH14 and MYH15 brings to completion the inventory of the MYH isoforms involved in sarcomeric architecture of skeletal muscles and provides an unambiguous molecular basis to study the contractile properties of slow-tonic fibres in mammals
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