Publications

ABSTRACT

Accurately modeling the complete gravitational-wave signal from precessing binary black holes through the late inspiral, merger, and ringdown remains a challenging problem. The lack of analytic solutions for the precession dynamics of generic double-spin systems, and the high dimensionality of the problem, obfuscate the incorporation of strong-field spin-precession information into semianalytic waveform models used in gravitational-wave data analysis. Previously, an effective precession spin χp was introduced to reduce the number of spin degrees of freedom. Here, we show that χp alone does not accurately reproduce higher-order multipolar modes, in particular the ones that carry strong imprints due to precession such as the (2,1)-mode. To improve the higher-mode content, and in particular to facilitate an accurate incorporation of precession effects in the strong-field regime into waveform models, we introduce a new dimensional reduction through an effective precession spin vector,

\vec{χ⊥}, which takes into account precessing spin information from both black holes. We show that this adapted effective precession spin (i) mimics the precession dynamics of the fully precessing configuration remarkably well, (ii) captures the signature features of precession in higher-order modes, and (iii) reproduces the final state of the remnant black hole with high accuracy for the overwhelming majority of configurations. We demonstrate the efficacy of this two-dimensional precession spin in the strong-field regime, paving the path for meaningful calibration of the precessing sector of semianalytic waveform models with a faithful representation of higher-order modes through merger and the remnant black hole spin.

ABSTRACT

Originally designed for waveform approximants, the effective precession parameter χp is the most commonly used quantity to characterize spin-precession effects in gravitational-wave observations of black-hole binary coalescences. We point out that the current definition of χp retains some, but not all, variations taking place on the precession timescale. We rectify this inconsistency and propose more general definitions that either fully consider or fully average those oscillations. Our generalized parameter χp∈[0,2] presents an exclusive region χp>1 that can only be populated by binaries with two precessing spins. We apply our prescriptions to current LIGO/Virgo events and find that posterior distributions of χp tend to show longer tails at larger values. This appears to be a generic feature, implying that (i) current χp measurement errors might be underestimated, but also that (ii) evidence for spin precession in current data might be stronger than previously inferred. Among the gravitational-wave events released to date, that which shows the most striking behavior is GW190521.

ABSTRACT

Gravitational waves enable tests of general relativity in the highly dynamical and strong-field regime. Using events detected by LIGO-Virgo up to 1 October 2019, we evaluate the consistency of the data with predictions from the theory. We first establish that residuals from the best-fit waveform are consistent with detector noise, and that the low- and high-frequency parts of the signals are in agreement. We then consider parametrized modifications to the waveform by varying post-Newtonian and phenomenological coefficients, improving past constraints by factors of ∼2; we also find consistency with Kerr black holes when we specifically target signatures of the spin-induced quadrupole moment. Looking for gravitational-wave dispersion, we tighten constraints on Lorentz-violating coefficients by a factor of ∼2.6 and bound the mass of the graviton to mg ≤1.76×10−23 eV/c^2

with 90% credibility. We also analyze the properties of the merger remnants by measuring ringdown frequencies and damping times, constraining fractional deviations away from the Kerr frequency to δf̂ 220 = 0.03+0.38−0.35 for the fundamental quadrupolar mode, and δf̂ 221 =0.04+0.27−0.32 for the first overtone; additionally, we find no evidence for postmerger echoes. Finally, we determine that our data are consistent with tensorial polarizations through a template-independent method. When possible, we assess the validity of general relativity based on collections of events analyzed jointly. We find no evidence for new physics beyond general relativity, for black hole mimickers, or for any unaccounted systematics.

ABSTRACT

We report on the population of the 47 compact binary mergers detected with a false-alarm rate 1/yr in the second LIGO--Virgo Gravitational-Wave Transient Catalog, GWTC-2. We observe several characteristics of the merging binary black hole (BBH) population not discernible until now. First, we find that the primary mass spectrum contains structure beyond a power-law with a sharp high-mass cut-off; it is more consistent with a broken power law with a break at 39.7+20.3−9.1 M⊙, or a power law with a Gaussian feature peaking at 33.1+4.0−5.6 M⊙ (90\% credible interval). While the primary mass distribution must extend to ∼65 M⊙ or beyond, only 2.9+3.5-1.7 % of systems have primary masses greater than 45 M⊙. Second, we find that a fraction of BBH systems have component spins misaligned with the orbital angular momentum, giving rise to precession of the orbital plane. Moreover, 12% to 44% of BBH systems have spins tilted by more than 90∘, giving rise to a negative effective inspiral spin parameter χeff. Under the assumption that such systems can only be formed by dynamical interactions, we infer that between 25% and 93% of BBH with non-vanishing |χeff|>0.01 are dynamically assembled. Third, we estimate merger rates, finding BBH = 23.9 +14.3-8.6 Gpc−3 yr−1 for BBH and BNS = 320+490−240 Gpc−3 yr−1 for binary neutron stars. We find that the BBH rate likely increases with redshift (85% credibility), but not faster than the star-formation rate (86% credibility). Additionally, we examine recent exceptional events in the context of our population models, finding that the asymmetric masses of GW190412 and the high component masses of GW190521 are consistent with our models, but the low secondary mass of GW190814 makes it an outlier.

ABSTRACT

We report on gravitational wave discoveries from compact binary coalescences detected by Advanced LIGO and Advanced Virgo in the first half of the third observing run (O3a) between 1 April 2019 15:00 UTC and 1 October 2019 15:00. By imposing a false-alarm-rate threshold of two per year in each of the four search pipelines that constitute our search, we present 39 candidate gravitational wave events. At this threshold, we expect a contamination fraction of less than 10%. Of these, 26 candidate events were reported previously in near real-time through GCN Notices and Circulars; 13 are reported here for the first time. The catalog contains events whose sources are black hole binary mergers up to a redshift of ~0.8, as well as events whose components could not be unambiguously identified as black holes or neutron stars. For the latter group, we are unable to determine the nature based on estimates of the component masses and spins from gravitational wave data alone. The range of candidate events which are unambiguously identified as binary black holes (both objects ≥3 M⊙) is increased compared to GWTC-1, with total masses from ∼14 M⊙ for GW190924_021846 to ∼150 M⊙for GW190521. For the first time, this catalog includes binary systems with significantly asymmetric mass ratios, which had not been observed in data taken before April 2019. We also find that 11 of the 39 events detected since April 2019 have positive effective inspiral spins under our default prior (at 90% credibility), while none exhibit negative effective inspiral spin. Given the increased sensitivity of Advanced LIGO and Advanced Virgo, the detection of 39 candidate events in ~26 weeks of data (~1.5 per week) is consistent with GWTC-1.

ABSTRACT

Gravitational-wave observations of merging compact binaries hold the key to precision measurements of the objects' masses and spins. General-relativistic precession, caused by spins misaligned with the orbital angular momentum, is considered a crucial tracer for determining the binary's formation history and environment, and it also improves mass estimates -- its measurement is therefore of particular interest with wide-ranging implications. Precession leaves a characteristic signature in the emitted gravitational-wave signal that is even more pronounced in binaries with highly unequal masses. The recent observations of GW190412 and GW190814 have confirmed the existence of such asymmetric compact binaries. Here, we perform a systematic study to assess the confidence in measuring precession in gravitational-wave observations of high mass ratio binaries and, our ability to measure the mass of the lighter companion in neutron star -- black hole type systems. Using Bayesian model selection, we show that precession can be decisively identified for low-mass binaries with mass ratios as low as 1:3 and mildly precessing spins with magnitudes ≲0.4, even in the presence of systematic waveform errors.