3,558 research outputs found
Hierarchical analysis of gravitational-wave measurements of binary black hole spin-orbit misalignments
Binary black holes may form both through isolated binary evolution and
through dynamical interactions in dense stellar environments. The formation
channel leaves an imprint on the alignment between the black hole spins and the
orbital angular momentum. Gravitational waves from these systems directly
encode information about the spin--orbit misalignment angles, allowing them to
be (weakly) constrained. Identifying sub-populations of spinning binary black
holes will inform us about compact binary formation and evolution. We simulate
a mixed population of binary black holes with spin--orbit misalignments
modelled under a range of assumptions. We then develop a hierarchical analysis
and apply it to mock gravitational-wave observations of these populations.
Assuming a population with dimensionless spin magnitudes of , we
show that tens of observations will make it possible to distinguish the
presence of subpopulations of coalescing binary black holes based on their spin
orientations. With observations it will be possible to infer the relative
fraction of coalescing binary black holes with isotropic spin directions
(corresponding to dynamical formation in our models) with a fractional
uncertainty of . Meanwhile, only observations are
sufficient to distinguish between extreme models---all binary black holes
either having exactly aligned spins or isotropic spin directions.Comment: 12 pages, 9 figures. Updated to match version published in MNRAS as
10.1093/mnras/stx176
Gravitational wave energy spectrum of a parabolic encounter
We derive an analytic expression for the energy spectrum of gravitational
waves from a parabolic Keplerian binary by taking the limit of the Peters and
Matthews spectrum for eccentric orbits. This demonstrates that the location of
the peak of the energy spectrum depends primarily on the orbital periapse
rather than the eccentricity. We compare this weak-field result to strong-field
calculations and find it is reasonably accurate (~10%) provided that the
azimuthal and radial orbital frequencies do not differ by more than ~10%. For
equatorial orbits in the Kerr spacetime, this corresponds to periapse radii of
rp > 20M. These results can be used to model radiation bursts from compact
objects on highly eccentric orbits about massive black holes in the local
Universe, which could be detected by LISA.Comment: 5 pages, 3 figures. Minor changes to match published version; figure
1 corrected; references adde
Parameter estimation on compact binary coalescences with abruptly terminating gravitational waveforms
Gravitational-wave astronomy seeks to extract information about astrophysical
systems from the gravitational-wave signals they emit. For coalescing
compact-binary sources this requires accurate model templates for the inspiral
and, potentially, the subsequent merger and ringdown. Models with
frequency-domain waveforms that terminate abruptly in the sensitive band of the
detector are often used for parameter-estimation studies. We show that the
abrupt waveform termination contains significant information that affects
parameter-estimation accuracy. If the sharp cutoff is not physically motivated,
this extra information can lead to misleadingly good accuracy claims. We also
show that using waveforms with a cutoff as templates to recover complete
signals can lead to biases in parameter estimates. We evaluate when the
information content in the cutoff is likely to be important in both cases. We
also point out that the standard Fisher matrix formalism, frequently employed
for approximately predicting parameter-estimation accuracy, cannot properly
incorporate an abrupt cutoff that is present in both signals and templates;
this observation explains some previously unexpected results found in the
literature. These effects emphasize the importance of using complete waveforms
with accurate merger and ringdown phases for parameter estimation.Comment: Very minor changes to match published versio
Inference on gravitational waves from coalescences of stellar-mass compact objects and intermediate-mass black holes
Gravitational waves from coalescences of neutron stars or stellar-mass black
holes into intermediate-mass black holes (IMBHs) of solar masses
represent one of the exciting possible sources for advanced gravitational-wave
detectors. These sources can provide definitive evidence for the existence of
IMBHs, probe globular-cluster dynamics, and potentially serve as tests of
general relativity. We analyse the accuracy with which we can measure the
masses and spins of the IMBH and its companion in intermediate-mass ratio
coalescences. We find that we can identify an IMBH with a mass above with confidence provided the massive body exceeds . For source masses above , the best measured
parameter is the frequency of the quasi-normal ringdown. Consequently, the
total mass is measured better than the chirp mass for massive binaries, but the
total mass is still partly degenerate with spin, which cannot be accurately
measured. Low-frequency detector sensitivity is particularly important for
massive sources, since sensitivity to the inspiral phase is critical for
measuring the mass of the stellar-mass companion. We show that we can
accurately infer source parameters for cosmologically redshifted signals by
applying appropriate corrections. We investigate the impact of uncertainty in
the model gravitational waveforms and conclude that our main results are likely
robust to systematics.Comment: 9 pages, 11 figure
Forward Modeling of Double Neutron Stars: Insights from Highly-Offset Short Gamma-Ray Bursts
We present a detailed analysis of two well-localized, highly offset short
gamma-ray bursts---GRB~070809 and GRB~090515---investigating the kinematic
evolution of their progenitors from compact object formation until merger.
Calibrating to observations of their most probable host galaxies, we construct
semi-analytic galactic models that account for star formation history and
galaxy growth over time. We pair detailed kinematic evolution with compact
binary population modeling to infer viable post-supernova velocities and
inspiral times. By populating binary tracers according to the star formation
history of the host and kinematically evolving their post-supernova
trajectories through the time-dependent galactic potential, we find that
systems matching the observed offsets of the bursts require post-supernova
systemic velocities of hundreds of kilometers per second. Marginalizing over
uncertainties in the stellar mass--halo mass relation, we find that the
second-born neutron star in the GRB~070809 and GRB~090515 progenitor systems
received a natal kick of at the 78\% and 91\%
credible levels, respectively. Applying our analysis to the full catalog of
localized short gamma-ray bursts will provide unique constraints on their
progenitors and help unravel the selection effects inherent to observing
transients that are highly offset with respect to their hosts.Comment: 18 pages, 7 figures, 1 table. ApJ, in pres
Evolutionary Origins of Binary Neutron Star Mergers: Effects of Common Envelope Efficiency and Metallicity
The formation histories of compact binary mergers, especially stellar-mass
binary-black hole mergers, have recently come under increased scrutiny and
revision. In this paper we revisit the question of the dominant formation
channel and efficiency of forming binary neutron-star mergers. We use the
stellar and binary evolution code MESA and implement an up-to-date and detailed
method for common envelope and mass transfer. We preform simulations for donor
masses between 8-20 solar masses with a neutron star companion of 1.4 and 2.0
solar masses, at two metallicities, using varying common envelope efficiencies,
and two prescriptions for electron-capture supernovae. In contrast to the case
of binary-black hole mergers, for a neutron star companion of 1.4 solar masses,
all binary neutron star mergers are formed following a common envelope phase,
while for a neutron star mass of 2.0 solar masses we identify a small subset of
mergers following only stable mass transfer if the neutron star receives a
large natal kick. Regardless of neutron star companion mass, we find that large
supernova natal kicks are favored in the formation of binary neutron star
mergers, and find more mergers at subsolar metallicity compared to solar.Comment: accepted to Ap
Rapid determination of LISA sensitivity to extreme mass ratio inspirals with machine learning
Gravitational wave observations of the inspiral of stellar-mass compact
objects into massive black holes (MBHs), extreme mass ratio inspirals (EMRIs),
enable precision measurements of parameters such as the MBH mass and spin. The
Laser Interferometer Space Antenna is expected to detect sufficient EMRIs to
probe the underlying source population, testing theories of the formation and
evolution of MBHs and their environments. Population studies are subject to
selection effects that vary across the EMRI parameter space, which bias
inference results if unaccounted for. This bias can be corrected, but
evaluating the detectability of many EMRI signals is computationally expensive.
We mitigate this cost by (i) constructing a rapid and accurate neural network
interpolator capable of predicting the signal-to-noise ratio of an EMRI from
its parameters, and (ii) further accelerating detectability estimation with a
neural network that learns the selection function, leveraging our first neural
network for data generation. The resulting framework rapidly estimates the
selection function, enabling a full treatment of EMRI detectability in
population inference analyses. We apply our method to an astrophysically
motivated EMRI population model, demonstrating the potential selection biases
and subsequently correcting for them. Accounting for selection effects, we
predict that LISA will measure the MBH mass function slope to a precision of
8.8%, the CO mass function slope to a precision of 4.6%, the width of the MBH
spin magnitude distribution to a precision of 10% and the event rate to a
precision of 12% with EMRIs at redshifts below z=6.Comment: 12 pages, 4 figure
Localization of Compact Binary Sources with Second Generation Gravitational-wave Interferometer Networks
GW170817 began gravitational-wave multimessenger astronomy. However, GW170817
will not be representative of detections in the coming years -- typical
gravitational-wave sources will be closer the detection horizon, have larger
localization regions, and (when present) will have correspondingly weaker
electromagnetic emission. In its design state, the gravitational-wave detector
network in the mid-2020s will consist of up to five similar-sensitivity
second-generation interferometers. The instantaneous sky-coverage by the full
network is nearly isotropic, in contrast to the configuration during the first
\change{three} observing runs. Along with the coverage of the sky, there are
also commensurate increases in the average horizon for a given binary mass. We
present a realistic set of localizations for binary neutron stars and neutron
star--black hole binaries, incorporating intra-network duty cycles and
selection effects on the astrophysical distributions. Based on the assumption
of an duty cycle, and that two instruments observe a signal above the
detection threshold, we anticipate a median of sq.\ deg.\ for binary
neutron stars, and -- sq.\ deg.\ for neutron star--black hole
(depending on the population assumed). These distributions have a wide spread,
and the best localizations, even for networks with fewer instruments, will have
localizations of -- sq.\ deg.\ range. The full five instrument network
reduces localization regions to a few tens of degrees at worst.Comment: 20 pages, 8 figures, 3 tables, accepted in Ap
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