38 research outputs found
Inferring spin tilts at formation from gravitational wave observations of binary black holes: Interfacing precession-averaged and orbit-averaged spin evolution
Two important parameters inferred from the gravitational wave signals of
binaries of precessing black holes are the spin tilt angles, i.e., the angles
at which the black holes' spin axes are inclined with respect to the binary's
orbital angular momentum. The LIGO-Virgo parameter estimation analyses
currently provide spin tilts at a fiducial reference frequency, often the
lowest frequency used in the data analysis. However, the most astrophysically
interesting quantities are the spin tilts when the binary was formed, which can
be significantly different from those at the reference frequency for strongly
precessing binaries. The spin tilts at formally infinite separation are a good
approximation to the tilts at formation in many formation channels and can be
computed efficiently for binary black holes using precession-averaged
evolution. Here, we present a new code for computing the tilts at infinity that
combines the precession-averaged evolution with orbit-averaged evolution at
high frequencies and illustrate its application to GW190521 and other binary
black hole detections from O3a. We have empirically determined the transition
frequency between the orbit-averaged and precession-averaged evolution to
produce tilts at infinity with a given accuracy. We also have regularized the
precession-averaged equations in order to obtain good accuracy for the very
close-to-equal-mass binary parameters encountered in practice. This
additionally allows us to investigate the singular equal-mass limit of the
precession-averaged expressions, where we find an approximate scaling of with the mass ratio .Comment: 25 pages, 16 figure
Effect of Ignoring Eccentricity in Testing General Relativity with Gravitational Waves
Detections of gravitational waves emitted from binary black hole coalescences
allow us to probe the strong-field dynamics of general relativity (GR). One can
compare the observed gravitational-wave signals with theoretical waveform
models to constrain possible deviations from GR. Any physics that is not
included in these waveform models might show up as apparent GR deviations. The
waveform models used in current tests of GR describe binaries on quasicircular
orbits, since most of the binaries detected by ground-based gravitational-wave
detectors are expected to have negligible eccentricities. Thus, a signal from
an eccentric binary in GR is likely to show up as a deviation from GR in the
current implementation of these tests. We study the response of four standard
tests of GR to eccentric binary black hole signals with the forecast O4
sensitivity of the LIGO-Virgo network. Specifically, we consider two
parameterized tests (TIGER and FTI), the modified dispersion relation test, and
the inspiral-merger-ringdown consistency test. To model eccentric signals, we
use non-spinning numerical relativity simulations from the SXS catalog with
three mass ratios , which we scale to a redshifted total mass of
and luminosity distance of Mpc. For each of these mass
ratios, we consider signals with eccentricities of and at
Hz. We find that signals with larger eccentricity lead to very significant
false GR deviations in most tests while signals having smaller eccentricity
lead to significant deviations in some tests. For the larger eccentricity
cases, one would even get a deviation from GR with TIGER at
credibility at a distance of Gpc. Thus, it will be necessary to
exclude the possibility of an eccentric binary in order to make any claim about
detecting a deviation from GR.Comment: 16 pages, 6 figures, version accepted by PR
Improving the NRTidal model for binary neutron star systems
Accurate and fast gravitational waveform (GW) models are essential to extract
information about the properties of compact binary systems that generate GWs.
Building on previous work, we present an extension of the NRTidal model for
binary neutron star (BNS) waveforms. The upgrades are: (i) a new closed-form
expression for the tidal contribution to the GW phase which includes further
analytical knowledge and is calibrated to more accurate numerical relativity
data than previously available; (ii) a tidal correction to the GW amplitude;
(iii) an extension of the spin-sector incorporating equation-of-state-dependent
finite size effects at quadrupolar and octupolar order; these appear in the
spin-spin tail terms and cubic-in-spin terms, both at 3.5PN. We add the new
description to the precessing binary black hole waveform model IMRPhenomPv2 to
obtain a frequency-domain precessing binary neutron star model. In addition, we
extend the SEOBNRv4_ROM and IMRPhenomD aligned-spin binary black hole waveform
models with the improved tidal phase corrections. Focusing on the new
IMRPhenomPv2_NRTidalv2 approximant, we test the model by comparing with
numerical relativity waveforms as well as hybrid waveforms combining tidal
effective-one-body and numerical relativity data. We also check consistency
against a tidal effective-one-body model across large regions of the BNS
parameter space.Comment: Accepted manuscrip
Binary Neutron Stars with Generic Spin, Eccentricity, Mass ratio, and Compactness - Quasi-equilibrium Sequences and First Evolutions
Information about the last stages of a binary neutron star inspiral and the
final merger can be extracted from quasi-equilibrium configurations and
dynamical evolutions. In this article, we construct quasi-equilibrium
configurations for different spins, eccentricities, mass ratios, compactnesses,
and equations of state. For this purpose we employ the SGRID code, which allows
us to construct such data in previously inaccessible regions of the parameter
space. In particular, we consider spinning neutron stars in isolation and in
binary systems; we incorporate new methods to produce highly eccentric and
eccentricity reduced data; we present the possibility of computing data for
significantly unequal-mass binaries; and we create equal-mass binaries with
individual compactness up to 0.23. As a proof of principle, we explore the
dynamical evolution of three new configurations. First, we simulate a
mass ratio which is the highest mass ratio for a binary neutron star evolved in
numerical relativity to date. We find that mass transfer from the companion
star sets in a few revolutions before merger and a rest mass of
is transferred between the two stars. This configuration
also ejects a large amount of material during merger, imparting a substantial
kick to the remnant. Second, we simulate the first merger of a precessing
binary neutron star. We present the dominant modes of the gravitational waves
for the precessing simulation, where a clear imprint of the precession is
visible in the (2,1) mode. Finally, we quantify the effect of an eccentricity
reduction procedure on the gravitational waveform. The procedure improves the
waveform quality and should be employed in future precision studies, but also
other errors, notably truncation errors, need to be reduced in order for the
improvement due to eccentricity reduction to be effective. [abridged]Comment: (37pages, 26 figures
Distinguishing binary black hole precessional morphologies with gravitational wave observations
The precessional motion of binary black holes can be classified into one of
three morphologies, based on the evolution of the angle between the components
of the spins in the orbital plane: Circulating, librating around 0, and
librating around . These different morphologies can be related to the
binary's formation channel and are imprinted in the binary's gravitational wave
signal. In this paper, we develop a Bayesian model selection method to
determine the preferred spin morphology of a detected binary black hole. The
method involves a fast calculation of the morphology which allows us to
restrict to a specific morphology in the Bayesian stochastic sampling. We
investigate the prospects for distinguishing between the different morphologies
using gravitational waves in the Advanced LIGO/Advanced Virgo network with
their plus-era sensitivities. For this, we consider fiducial high- and low-mass
binaries having different spin magnitudes and signal-to-noise ratios (SNRs). We
find that in the cases with high spin and high SNR, the true morphology is
strongly favored with Bayes factors compared to both
alternative morphologies when the binary's parameters are not close to the
boundary between morphologies. However, when the binary parameters are close to
the boundary between morphologies, only one alternative morphology is strongly
disfavored. In the low-spin, high-SNR cases, the true morphology is still
favored with a Bayes factor compared to one alternative
morphology. We also consider the gravitational wave signal from GW200129_065458
that has some evidence for precession (modulo data quality issues) and find
that there is no preference for a specific morphology. Our method for
restricting the prior to a given morphology is publicly available through an
easy-to-use Python package called bbh_spin_morphology_prior. (Abridged)Comment: 14 pages, 5 figures, version accepted by PR
Distinguishing binary black hole precessional morphologies with gravitational wave observations
The precessional motion of binary black holes can be classified into one of three morphologies, based on the evolution of the angle between the components of the spins in the orbital plane: Circulating, librating around 0, and librating around π. These different morphologies can be related to the binary’s formation channel and are imprinted in the binary’s gravitational wave signal. In this paper, we develop a Bayesian model selection method to determine the preferred spin morphology of a detected binary black hole. The method involves a fast calculation of the morphology which allows us to restrict to a specific morphology in the Bayesian stochastic sampling. We investigate the prospects for distinguishing between the different morphologies using gravitational waves in the Advanced LIGO/Advanced Virgo network with their plus-era sensitivities. For this, we consider fiducial high- and low-mass binaries having different spin magnitudes and signal-to-noise ratios (SNRs). We find that in the cases with high spin and high SNR, the true morphology is strongly favored with log10 Bayes factors ≳ 4 compared to both alternative morphologies when the binary’s parameters are not close to the boundary between morphologies. However, when the binary parameters are close to the boundary between morphologies, only one alternative morphology is strongly disfavored. In the low-spin, high-SNR cases, the true morphology is still favored with a log10 Bayes factor ∼ 2 compared to one alternative morphology, while in the low-SNR cases the log10 Bayes factors are at most ∼1 for many binaries. We also consider the gravitational wave signal from GW200129_065458 that has some evidence for precession (modulo data quality issues) and find that there is no preference for a specific morphology. Our method for restricting the prior to a given morphology is publicly available through an easy-to-use python package called bbh_spin_morphology_prior
Constraining black hole mimickers with gravitational wave observations
LIGO and Virgo have recently observed a number of gravitational wave (GW)
signals that are fully consistent with being emitted by binary black holes
described by general relativity. However, there are theoretical proposals of
exotic objects that can be massive and compact enough to be easily confused
with black holes. Nevertheless, these objects differ from black holes in having
nonzero tidal deformabilities, which can allow one to distinguish binaries
containing such objects from binary black holes using GW observations. Using
full Bayesian parameter estimation, we investigate the possibility of
constraining the parameter space of such "black hole mimickers" with upcoming
GW observations. Employing perfect fluid stars with a polytropic equation of
state as a simple model that can encompass a variety of possible black hole
mimickers, we show how the observed masses and tidal deformabilities of a
binary constrain the equation of state. We also show how such constraints can
be used to rule out some simple models of boson stars.Comment: 5 + 4 pages, 4 figures; v2: small change