Bpass predictions for binary black hole mergers

We report on the population properties of compact binary mergers inferred from gravitational-wave observations of these systems during the first three LIGO-Virgo observing runs. The Gravitational-Wave Transient Catalog 3 (GWTC-3) contains signals consistent with three classes of binary mergers: binary black hole, binary neutron star, and neutron star–black hole mergers. We infer the binary neutron star merger rate to be between 10 and 1700 Gpc−3 yr−1 and the neutron star–black hole merger rate to be between 7.8 and 140 Gpc−3 yr−1, assuming a constant rate density in the comoving frame and taking the union of 90% credible intervals for methods used in this work. We infer the binary black hole merger rate, allowing for evolution with redshift, to be between 17.9 and 44 Gpc−3 yr−1 at a fiducial redshift (z=0.2). The rate of binary black hole mergers is observed to increase with redshift at a rate proportional to (1+z)κ with κ=2.9−1.8+1.7 for z≲1. Using both binary neutron star and neutron star–black hole binaries, we obtain a broad, relatively flat neutron star mass distribution extending from 1.2−0.2+0.1 to 2.0−0.3+0.3M⊙. We confidently determine that the merger rate as a function of mass sharply declines after the expected maximum neutron star mass, but cannot yet confirm or rule out the existence of a lower mass gap between neutron stars and black holes. We also find the binary black hole mass distribution has localized over- and underdensities relative to a power-law distribution, with peaks emerging at chirp masses of 8.3−0.5+0.3 and 27.9−1.8+1.9M⊙. While we continue to find that the mass distribution of a binary’s more massive component strongly decreases as a function of primary mass, we observe no evidence of a strongly suppressed merger rate above approximately 60M⊙, which would indicate the presence of a upper mass gap. Observed black hole spins are small, with half of spin magnitudes below χi≈0.25. While the majority of spins are preferentially aligned with the orbital angular momentum, we infer evidence of antialigned spins among the binary population. We observe an increase in spin magnitude for systems with more unequal-mass ratio. We also observe evidence of misalignment of spins relative to the orbital angular momentum. Published by the American Physical Society 2023

Detections of gravitational-wave signals from compact binary coalescences have enabled us to study extreme astrophysical phenomena and explore fundamental physics. A crucial requisite for these studies is to have accurate signal models with characteristic morphologies, which have been challenging for many decades, and researchers are still endeavoring to incorporate important physics. Therefore, morphology-independent methods have been developed for identifying a signal and its reconstruction. The reconstructed signal allows us to test the agreement between the observed signal and the waveform posterior samples from parameter estimation. These methods model observed signals using a nearly orthogonal wavelet basis in the frame of continuous wavelet transformation. Here, we propose log-uniform scales to construct the wavelets, which are are highly redundant (nonorthogonal) compared to the conventional octave scales but more efficient for reconstructing the signals at high frequencies. And we introduce a semi-model-dependent reconstruction method using the posterior samples of the events, where we model the signal using Gabor-Morlet wavelets with log-uniform scales. We demonstrate the ability to detect deviation using a numerical simulation of an eccentric binary black hole merger, where the signal in the data does not belong to the search template waveform manifold. Finally, we apply this method to each binary black hole merger event in GWTC-1. We have found that the signal produced by the GW150914 event has 96% agreement with the waveform posterior samples. As the detector sensitivity improves and the detected population of black hole mergers grows, we expect the proposed method will provide even stronger tests.

Population III (Pop. III) binary stars likely produced the first stellar-born binary black hole (BBH) mergers in the Universe. Here, we quantify the main sources of uncertainty for the merger rate density evolution and mass spectrum of Pop. III BBHs by considering four different formation histories and 11 models of the initial orbital properties of Pop. III binary stars. The uncertainty on the orbital properties affects the BBH merger rate density by up to two orders of magnitude, models with shorter orbital periods leading to higher BBH merger rates. The uncertainty on the star formation history has a substantial impact on both the shape and the normalization of the BBH merger rate density: the peak of the merger rate density shifts from z ∼ 8 up to z ∼ 16 depending on the assumed star formation rate, while the maximum BBH merger rate density for our fiducial binary population model spans from ∼2 to ∼30 Gpc−3 yr−1. The typical BBH masses are not affected by the star formation rate model and only mildly influenced by the binary population parameters. The primary black holes born from Pop. III stars tend to be rather massive (30–40 M⊙) with respect to those born from metal-rich stars (8–10 M⊙). We estimate that the Einstein Telescope will detect 10–104 Pop. III BBH mergers per year, depending on the star formation history and binary star properties.

Testing black hole’s charged property is a fascinating topic in modified gravity and black hole astrophysics. In the first Gravitational-Wave Transient Catalog (GWTC-1), ten binary black hole merger events have been formally reported, and these gravitational wave signals have significantly enhanced our understanding of the black hole. In this paper, we try to constrain the amount of electric charge with the parameterized post-Einsteinian framework by treating the electric charge as a small perturbation in a Bayesian way. We find that the current limits in our work are consistent with the result of Fisher information matrix method in previous works. We also develop a waveform model considering a leading order charge effect for binary black hole inspiral.

Understanding the characteristics of the remnant black hole formed in a binary black hole merger is crucial for conducting gravitational wave astronomy. Typically, models of remnant black holes provide information about their mass, spin, and kick velocity. However, other information related to the supertranslation symmetries of the BMS group, such as the memory effect, is also important for characterizing the final state of the system. In this work, we build a model of the BMS transformation that maps a binary black hole's inspiral frame to the remnant black hole's canonical rest frame. Training data for this model are created using high-precision numerical relativity simulations of quasicircular systems with mass ratios $q\ensuremath{\le}8$ and spins parallel to the orbital angular momentum with magnitudes ${\ensuremath{\chi}}_{1}$, ${\ensuremath{\chi}}_{2}\ensuremath{\le}0.8$. We use Gaussian process regression to model the BMS transformations over the three-dimensional parameter space $(q,{\ensuremath{\chi}}_{1}^{z},{\ensuremath{\chi}}_{2}^{z})$. The physics captured by this model is strictly nonperturbative and cannot be obtained from post-Newtonian approximations alone, as it requires knowledge of the strong nonlinear effects that are sourced during the merger. Apart from providing the first model of the supertranslation induced by a binary black hole merger, we also find that the kick velocities predicted using Cauchy-characteristic evolution waveforms are, on average, $\ensuremath{\sim}5%$ larger than the ones obtained from extrapolated waveforms. Our work has broad implications for improving gravitational wave models and studying the large-scale impact of memory, such as on the cosmological background. The fits produced in this work are available through the python package surfinbh under the name nrsur3dq8bmsremnant.

Since the first detection of the binary black hole merger event GW150914 in 2015, gravitational wave astronomy has rapidly advanced, with 93 gravitational wave events detected until O3. The continuous improvement of gravitational wave detectors and the emergence of a new generation of detectors will expand our ability to observe the universe. This study uses the cWB pipeline as an example to explore the core algorithms of unmodeled gravitational wave searches and the computation of background and event significance. Furthermore, we briefly review its applications for various gravitational wave sources, including high-eccentricity compact binary mergers, core-collapse supernovae, hyperbolic encounters, pulsar glitches, microlensing, and echoes. Finally, this study discusses the future applications of machine learning in unmodeled gravitational wave searches and the possible adaption of the modular, Python-based PycWB pipeline for future space-based gravitational wave detectors.

We demonstrate that in binary black hole (BBH) mergers there is a direct correlation between the frequency of the gravitational wave at peak amplitude and the quasi-normal mode frequency and damping time of the final black hole. Since the ringing frequency and damping time of a black hole are related to its mass and spin, the correlation discovered also provides a connection between the parameters of the final black hole and the frequency of the gravitational wave at peak amplitude. This correlation could potentially assist with the analysis of gravitational wave observations from BBH mergers.

A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.

Despite the increasing number of gravitational wave (GW) detections, the astrophysical origin of binary black hole (BBH) mergers remains elusive. A promising formation channel for BBHs is inside accretion discs around supermassive black holes, that power active galactic nuclei (AGN). In this paper, we test for the first time the spatial correlation between observed GW events and AGN. To this end, we assemble all sky catalogues with 1,412 (242) AGN with a bolometric luminosity greater than 1045.5erg s−1 ($10^{46}\, {\rm erg\, s}^{-1}$) with spectroscopic redshift of z ≤ 0.3 from the Milliquas catalogue, version 7.7b. These AGN are cross-matched with localization volumes of BBH mergers observed in the same redshift range by the LIGO and Virgo interferometers during their first three observing runs. We find that the fraction of the detected mergers originated in AGN brighter than $10^{45.5}\, {\rm erg\, s}^{-1}$ ($10^{46}\, {\rm erg\, s}^{-1}$) cannot be higher than 0.49 (0.17) at a 95 per cent credibility level. Our upper limits imply a limited BBH merger production efficiency of the brightest AGN, while most or all GW events may still come from lower luminosity ones. Alternatively, the AGN formation path for merging stellar-mass BBHs may be actually overall subdominant in the local Universe. To our knowledge, ours are the first observational constraints on the fractional contribution of the AGN channel to the observed BBH mergers.

We determine the mass-ratio, eccentricity and binary inclination angles that maximize the contribution of the higher-order waveform multipoles $(\ell, \, |m|)= \{(2,\,2),\, (2,\,1),\, (3,\,3),\, (3,\,2), \, (3,\,1),\, (4,\,4),\, (4,\,3),\, (4,\,2),\,(4,\,1)\}$ for the gravitational wave detection of eccentric binary black hole mergers. We carry out this study using numerical relativity waveforms that describe non-spinning black hole binaries with mass-ratios $1\leq q \leq 10$, and orbital eccentricities as high as $e_0=0.18$ fifteen cycles before merger. For stellar-mass, asymmetric mass-ratio, binary black hole mergers, and assuming LIGO's Zero Detuned High Power configuration, we find that in regions of parameter space where black hole mergers modeled with $\ell=|m|=2$ waveforms have vanishing signal-to-noise ratios, the inclusion of $(\ell, \, |m|)$ modes enables the observation of these sources with signal-to-noise ratios that range between 30\% to 45\% the signal-to-noise ratio of optimally oriented binary black hole mergers modeled with $\ell=|m|=2$ numerical relativity waveforms. Having determined the parameter space where $(\ell, \, |m|)$ modes are important for gravitational wave detection, we construct waveform signals that describe these astrophysically motivate scenarios, and demonstrate that these topologically complex signals can be detected and characterized in real LIGO noise with deep learning algorithms.

In classical numerical relativity, marginally outer trapped surfaces (MOTSs) are the main tool to locate and characterize black holes. For five decades it has been known that during a binary merger, a new outer horizon forms around the initial apparent horizons of the individual holes once they are sufficiently close together. However the ultimate fate of those initial horizons has remained a subject of speculation. Recent axisymmetric studies have shed new light on this process and this pair of papers essentially completes that line of research: we resolve the key features of the post-swallowing axisymmetric evolution of the initial horizons. This first paper introduces a new shooting-method for finding axisymmetric MOTSs along with a reinterpretation of the stability operator as the analogue of the Jacobi equation for families of MOTSs. Here, these tools are used to study exact solutions and initial data. In the sequel paper [Phys. Rev. D 104, 084084 (2021)] they are applied to black hole mergers.

With the rapid development of deep learning technology, more and more researchers apply it to gravitational wave (GW) data analysis. Previous studies focused on a single deep learning model. In this paper we design an ensemble algorithm combining a set of convolutional neural networks for GW signal recognition. The whole ensemble model consists of two subensemble models. Each subensemble model is also an ensemble model of deep learning. The two subensemble models treat data of Hanford and Livinston detectors, respectively. Proper voting scheme is adopted to combine the two subensemble models to form the whole ensemble model. We apply this ensemble model to all reported GW events in the first observation and second observation runs (O1/O2) by LIGO-VIRGO Scientific Collaboration. We find that the ensemble algorithm can clearly identify all binary black hole merger events except GW170818. We also apply the ensemble model to one month (August 2017) data of O2. No false trigger happens, although only O1 data are used for training. Our test results indicate that the ensemble learning algorithms can be used in real-time GW data analysis.

Recent gravitational wave (GW) observations include possible detections of black hole—neutron star binary mergers. As with binary black hole mergers, numerical simulations help characterize the sources. For binary systems with neutron star components, the simulations help to predict the imprint of tidal deformations and disruptions on the GW signals. In a previous study, we investigated how the mass of the black hole has an impact on the disruption of the neutron star and, as a consequence, on the shape of the GWs emitted. We extend these results to study the effects of varying the compactness of the neutron star. We consider neutron star compactness in the 0.113–0.2 range for binaries with mass ratios of 3 and 5. As the compactness and the mass ratio increase, the binary system behaves during the late inspiral and merger more like a black hole binary. For the cases with the least compact neutron star, the GWs emitted, in terms of mismatches, are the most distinguishable from those by a binary black hole. The disruption of the star significantly suppresses the kicks on the final black hole. The disruption also affects, although not dramatically, the spin of the final black hole. Lastly, for neutron stars with low compactness, the quasi-normal ringing of the black hole after the merger does not show a clean quasi-normal ringing because of the late accretion of debris from the neutron star.

With ground-based gravitational wave detectors at design sensitivity, and a space-based detector in planning stages, the need for accurate gravitational wave templates for signal recognition by detector pipelines has become an urgent problem. With that in mind, and the fact that binary black hole inspirals and mergers are the strongest potential source for gravitational wave signals for online detectors, my research has focused on improving the accuracy and well-posedness of numerical simulations, and on the generation of grav- itational waveforms from numerical simulations both for detector template generation and for astrophysical predictions. For simulations of highly dynamical relativistic vacuum space-times I derived accu- rate and well-posed formulations of the Einstein equations for numerical evolutions. I herein propose a set of well-posed, constraint-preserving boundary conditions for artifi- cial boundaries for a first order in time and second order in space ‘generalized harmonic’ formulation of the Einstein equations. I tested these conditions both for black hole space- times and for a series of robust stability tests, and show that these conditions reduce noise, reduce constraint violation, and increase stability for relativistic simulations. Addition- ally, I propose novel, well-posed, constraint-preserving boundary conditions for the more commonly used BSSN evolution system for standard “1 + log” and Gamma-driver gauge conditions. I carried out numerical evolutions of symmetric and asymmetric binary black hole mergers in large numbers to explore the parameter space of binary black hole inspirals and derive a statistical and phenomenological view of the physical qualities of binary merger remnants. I ran binary black hole inspiral simulations using both quasi-circular and post- Newtonian derived initial orbital binary inspiral parameters, and “puncture” initial data, and extracted physics from a number of initial data sequences in order to establish bounds on phenomenological formulae for the final spin and recoil velocity of merged black holes from arbitrary initial data parameters. With the data from those parameter studies we focus on gravitational-wave emission to quantify how much spin effects contribute to the signal-to-noise ratio and to the relative event rates for the representative ranges in masses and detectors. I show that equal-spin binaries with maximum spin aligned with the orbital angular momentum are more than “three times as loud” as the corresponding binaries with anti-aligned spins. Finally, we derive a simple expression for the energy radiated in gravitational waves and find that the binaries have efficiencies Erad/M between 3.6% and 10%. Finally, I present an analytical inspiral-merger-ringdown gravitational waveforms from black-hole (BH) binaries with non-precessing spins by matching a post-Newtonian description of the inspiral to our numerical calculations, we obtain a waveform family with a conveniently small number of physical parameters. These waveforms will allow us to detect a larger parameter space of BH binary coalescence, to explore various sci- entific questions related to GW astronomy, and could dramatically improve the expected detection rates of GW detectors.

In vacuum, the gravitational recoil of the final black hole from the merger of two black holes depends exclusively on the mass ratio and spins of the coalescing black holes, and on the eccentricity of the binary. If matter is present, accretion by the merging black holes may modify significantly their masses and spins, altering both the dynamics of the binary and the gravitational recoil of the remnant black hole. This paper considers such a scenario. We investigate the effects on the kick of the final black hole from immersing the binary in a scalar field cloud. We consider two types of configurations: one with nonspinning and unequal-mass black holes, and a second with equal mass and spinning holes. For both types, we investigate how the gravitational recoil of the final black hole changes as we vary the energy density of the scalar field. We find that the accretion of the scalar field by the merging black holes could have a profound effect. For the nonspinning, unequal-mass binary black holes, the kicks are in general larger than in the vacuum case, with speeds of $\ensuremath{\sim}1,200\text{ }\text{ }\mathrm{km}/\mathrm{s}$ for binaries with mass ratio $2\ensuremath{\mathbin:}1$, 1 order of magnitude larger than in vacuum. For equal mass, binaries with black holes with spins aligned with the orbital angular momentum, kicks larger than in vacuum are also found. For systems with spins in the superkick configuration, the scalar field triggers a similar dependence of the kicks with the entrance angle at merger as in the vacuum case but in this case depending on the strength of the scalar field.