176 research outputs found
Inferences about supernova physics from gravitational-wave measurements: GW151226 spin misalignment as an indicator of strong black-hole natal kicks
The inferred parameters of the binary black hole GW151226 are consistent with
nonzero spin for the most massive black hole, misaligned from the binary's
orbital angular momentum. If the black holes formed through isolated binary
evolution from an initially aligned binary star, this misalignment would then
arise from a natal kick imparted to the first-born black hole at its birth
during stellar collapse. We use simple kinematic arguments to constrain the
characteristic magnitude of this kick, and find that a natal kick km/s must be imparted to the black hole at birth to produce misalignments
consistent with GW151226. Such large natal kicks exceed those adopted by
default in most of the current supernova and binary evolution models.Comment: 6 pages, 2 figures. Accepted for publication in PRL. Selected in
physics.aps.or
Inferences about the distribution, merger rate, and evolutionary processes of compact binaries from gravitational wave observations
We are living through the dawn of the era of gravitational wave astronomy. Our first glances through this new window upon the sky has revealed a new population of objects. Since it first began observing in late 2015, the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected gravitational waves three times, along with an additional strong candidate -- and there shall be orders of magnitude more in the years to come. In all four cases, the waveform\u27s signature is consistent with general relativity\u27s predictions for the merging of two black holes. Through parameter estimation studies, estimates on features such as the black holes\u27 masses and spins have been determined. At least two of the black hole pairs lie above the mass range spanned by comparable black holes observed through traditional means. This suggests they constitute a separate population, either too elusive or rare to be found with traditional telescopes.
The most natural questions to ask about these black holes -- how did they form, how many of them are there, and how can they be categorized -- remain open ended. We know black holes can form when massive stars die, so it\u27s most natural to claim stars as their progenitors. Since we now know black holes merge into larger black holes, could it be the case that they formed from previous mergers? Were the two black holes part of a binary from their birth, or did they become coupled later on in life? The measurements provided by LIGO can help answer these questions and more.
Throughout this thesis, I will describe and demonstrate results from a number of novel methods whose purpose is to better understand these black holes and their progenitors. At their heart, these methods give answers to a few, critical questions. a) What is the overall rate at which these objects merge? b) What is the range of values these objects\u27 properties can take, and how are they distributed? c) Given a number of physical models, how can we evaluate the performance of each relative to the others, and determine which gives the best description of reality
Measuring the Population Properties of Merging Compact Binaries with Gravitational Wave Observations
Since the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first direct detection of gravitational waves in 2015, the era of gravitational wave astronomy has begun. LIGO and its counterpart Virgo are detecting an ever-growing sample of merging compact binaries: binary black holes, binary neutron stars, and neutron star--black hole binaries. Each individual detection can be compared against simulated signals with known properties, in order to measure the binary\u27s properties. In order to understand the sample of detections as a whole, however, ensemble methods are needed.
The properties measured from these binary systems have large measurement errors, and the sensitivity of gravitational wave detectors are highly property-dependent, resulting in large selection biases. This dissertation applies the technique of hierarchical Bayesian modeling in order to constrain the underlying, unbiased population of merging compact binaries. We use a number of models to constrain the merger rate, mass distribution, and spin distribution for binary black holes and binary neutron stars. We also use tidal information present in binary neutron stars in order to self-consistently constrain the nuclear equation of state
Iteratively Comparing Gravitational-Wave Observations to the Evolution of Massive Stellar Binaries
Gravitational-wave observations have the capability to strongly differentiate
between different concrete assumptions for how binary compact objects form. The
agreement of observations to different models of the evolution of massive
stellar binaries leading to the formation of compact binaries can be
characterized by a Bayesian marginal likelihood. In this work, we show how to
carefully interpolate this marginal likelihood between choices of binary
evolution model parameters, enabling the analysis of their posterior
distributions between expensive binary evolution simulations. Using the
StarTrack binary evolution code, we compare one- and four-dimensional binary
evolution models to the compact binary mergers reported in recent
gravitational-wave observing runs, considering merger detection rates and mass
distributions. We demonstrate that the predicted detection rates and mass
distribution of simulated binaries are effective in constraining binary
evolution formation. We first consider a one-dimensional model, studying the
effect of SuperNova (SN) kick velocity () and follow this up with
a four-dimensional study of , mass transfer efficiency ()
and angular momentum ejection () during Roche-lobe accretion, and an
observation-driven reduction in the mass-loss rate from stellar wind
(). Of those four formation parameters, we find that three of them
(, , and ) can be efficiently constrained at this
time. After initially sampling from a uniform prior in the space of these
parameters, we refined our sampling by iteratively fitting a truncated
Gaussian, and sampling from those Gaussians to propose new simulations with
each iteration. Our maximum likelihood simulation (K0559) has parameters:
km/s, (indicating efficient mass
transfer), and
Spin orientations of merging black holes formed from the evolution of stellar binaries
We study the expected spin misalignments of merging binary black holes (BHs)
formed in isolation by combining state-of-the-art population-synthesis models
with efficient post-Newtonian evolutions, thus tracking sources from stellar
formation to gravitational-wave detection. We present extensive predictions of
the properties of sources detectable by both current and future
interferometers. We account for the fact that detectors are more sensitive to
spinning BH binaries with suitable spin orientations and find that this
significantly impacts the population of sources detectable by LIGO, while this
is not the case for 3rd-generation detectors. We find that three formation
pathways, differentiated by the order of core collapse and common-envelope
phases, dominate the observed population, and that their relative importance
critically depends on the recoils imparted to BHs at birth. Our models suggest
that measurements of the "effective-spin" parameter will allow
for powerful constraints. For instance, we find that the role of spin
magnitudes and spin directions in can be largely disentangled,
and that the symmetry of the effective-spin distribution is a robust indicator
of the binary's formation history. Our predictions for individual spin
directions and their precessional morphologies confirm and extend early toy
models, while exploring substantially more realistic and broader sets of
initial conditions. Our main conclusion is that specific subpopulations of BH
binaries will exhibit distinctive precessional dynamics: these classes include
(but are not limited to) sources where stellar tidal interactions act on
sufficiently short timescales, and massive binaries produced in pulsational
pair-instability supernovae. Measurements of BH spin orientations have enormous
potential to constrain specific evolutionary processes in the lives of massive
binary stars.Comment: 21 pages, 16 figures. Database and python code available at
https://github.com/dgerosa/spops - Published in PR
Nitric Oxide Isotopic Analyzer Based on a Compact Dual-Modulation Faraday Rotation Spectrometer
We have developed a transportable spectroscopic nitrogen isotopic analyzer. The spectrometer is based on dual-modulation Faraday rotation spectroscopy of nitric oxide isotopologues with near shot-noise limited performance and baseline-free operation. Noise analysis indicates minor isotope (15NO) detection sensitivity of 0.36 ppbv·Hz−1/2, corresponding to noise-equivalent Faraday rotation angle (NEA) of 1.31 × 10−8 rad·Hz−1/2 and noise-equivalent absorbance (αL)min of 6.27 × 10−8 Hz−1/2. White-noise limited performance at 2.8× the shot-noise limit is observed up to ~1000 s, allowing reliable calibration and sample measurement within the drift-free interval of the spectrometer. Integration with wet-chemistry based on acidic vanadium(III) enables conversion of aqueous nitrate/nitrite samples to gaseous NO for total nitrogen isotope analysis. Isotopic ratiometry is accomplished via time-multiplexed measurements of two NO isotope transitions. For 5 μmol potassium nitrate samples, the instrument consistently yields ratiometric precision below 0.3‰, thus demonstrating potential as an in situ diagnostic tool for environmental nitrogen cycle studies
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