Gravitational wave templates used in current searches for binary black holes omit the effects of precession of the orbital plane and higher-order modes. While this omission seems not to impact the ...detection of sources having mass ratios and spins similar to those of GW150914, even for total masses M>200 M⊙, we show that it can cause large fractional losses of sensitive volume for binaries with mass ratio q≥4 and M>100 M⊙, measured in the detector frame. For the highest precessing cases, this is true even when the source is face-on to the detector. Quantitatively, we show that the aforementioned omission can lead to fractional losses of sensitive volume of ∼15%, reaching >25% for the worst cases studied. Loss estimates are obtained by evaluating the effectualness of the SEOBNRv2-ROM double spin model, currently used in binary black hole searches, towards gravitational wave signals from precessing binaries computed by means of numerical relativity. We conclude that, for sources with q≥4, a reliable search for binary black holes heavier than M>100 M⊙ needs to consider the effects of higher-order modes and precession. The latter seems especially necessary when Advanced LIGO reaches its design sensitivity.
Pair-instability supernovae are thought to restrict the formation of black holes in the mass range ∼ 50 - 135 M . However, black holes with masses within this "high mass gap" are expected to form as ...the remnants of binary black hole mergers. These remnants can merge again dynamically in densely populated environments such as globular clusters. The hypothesis that the binary black hole merger GW190521 formed dynamically is supported by its high mass. Orbital eccentricity can also be a signature of dynamical formation, since a binary that merges quickly after becoming bound may not circularize before merger. In this work, we measure the orbital eccentricity of GW190521. We find that the data prefer a signal with eccentricity e ≥ 0.1 at 10 Hz to a nonprecessing, quasi-circular signal, with a log Bayes factor ln = 5.0 . When compared to precessing, quasi-circular analyses, the data prefer a nonprecessing, e ≥ 0.1 signal, with log Bayes factors ln 2 . Using injection studies, we find that a nonspinning, moderately eccentric (e = 0.13) GW190521-like binary can be mistaken for a quasi-circular, precessing binary. Conversely, a quasi-circular binary with spin-induced precession may be mistaken for an eccentric binary. We therefore cannot confidently determine whether GW190521 was precessing or eccentric. Nevertheless, since both of these properties support the dynamical formation hypothesis, our findings support the hypothesis that GW190521 formed dynamically.
Coalescing binary black holes emit anisotropic gravitational radiation. This causes a net emission of linear momentum that produces a gradual acceleration of the source. As a result, the final ...remnant black hole acquires a characteristic velocity known as recoil velocity or gravitational kick. The symmetries of gravitational wave emission are reflected in the interactions of the gravitational wave modes emitted by the binary. In this Letter, we make use of the rich information encoded in the higher-order modes of the gravitational wave emission to infer the component of the kick along the line of sight (or radial kick). We do this by performing parameter inference on simulated signals given by numerical relativity waveforms for nonspinning binaries using numerical relativity templates of aligned-spin (nonprecessing) binary black holes. We find that for suitable sources, namely those with mass ratio q≥2 and total mass M∼100 M_{⊙}, and for modest radial kicks of 120 km/s, the 90% credible intervals of our posterior probability distributions can exclude a zero kick at a signal-to-noise ratio of 15, using a single Advanced LIGO detector working at its early sensitivity. The measurement of a nonzero radial kick component would provide the first observational signature of net transport of linear momentum by gravitational waves away from their source.
Current searches for the gravitational-wave signature of compact binary mergers rely on matched-filtering data from interferometric observatories with sets of modeled gravitational waveforms. These ...searches currently use model waveforms that do not include the higher-order mode content of the gravitational-wave signal. Higher-order modes are important for many compact binary mergers and their omission reduces the sensitivity to such sources. In this work we explore the sensitivity loss incurred from omitting higher-order modes. We present a new method for searching for compact binary mergers using waveforms that include higher-order mode effects, and evaluate the sensitivity increase that using our new method would allow. We find that, when evaluating sensitivity at a constant rate-of-false alarm, and when including the fact that signal-consistency tests can reject some signals that include higher-order mode content, we observe a sensitivity increase of up to a factor of 2 in volume for high mass ratio, high total-mass systems. For systems with equal mass, or with total mass ∼50 M⊙, we see more modest sensitivity increases, <10%, which indicates that the existing search is already performing well. Our new search method is also directly applicable in searches for generic compact binaries.
Current template-based gravitational wave searches for compact binary coalescences use waveform models that omit the higher order modes content of the gravitational radiation emitted, considering ...only the quadrupolar (scriptl,m) = (2,2) modes. We study the effect of such omission for the case of aligned-spin compact binary coalescence searches for equal-spin (and nonspinning) binary black holes in the context of two versions of Advanced LIGO: the upcoming 2015 version, known as early Advanced LIGO (eaLIGO) and its zero-detuned high-energy power version, which we will refer to as Advanced LIGO (AdvLIGO). In addition, we study the case of a nonspinning search for initial LIGO (iLIGO). We do this via computing the effectualness of the aligned-spin SEOBNRv1 reduced order model waveform family, which only considers quadrupolar modes, toward hybrid post-Newtonian/numerical relativity waveforms which contain higher order modes. We find that for all LIGO versions losses of more than 10% of events occur in the case of AdvLIGO for mass ratio q > or = 6 and total mass M > or = 100M sub(middot in circle) due to the omission of higher modes, this region of the parameter space being larger for eaLIGO and iLIGO. Moreover, while the maximum event loss observed over the explored parameter space for AdvLIGO is of 15% of events, for iLIGO and eaLIGO, this increases up to (39,23)%. We find that omission of higher modes leads to observation-averaged systematic parameter biases toward lower spin, total mass, and chirp mass. For completeness, we perform a preliminar, nonexhaustive comparison of systematic biases to statistical errors. We find that, for a given signal-to-noise ratio, systematic biases dominate over statistical errors at much lower total mass for eaLIGO than for AdvLIGO.
The "no-hair" theorem states that astrophysical black holes are fully characterized by just two numbers: their mass and spin. The gravitational-wave emission from a perturbed black-hole consists of a ...superposition of damped sinusoids, known as quasinormal modes. Quasinormal modes are specified by three integers (ℓ,m,n): the (ℓ,m) integers describe the angular properties and (n) specifies the (over)tone. If the no-hair theorem holds, the frequencies and damping times of quasinormal modes are determined uniquely by the mass and spin of the black hole, while phases and amplitudes depend on the particular perturbation. Current tests of the no-hair theorem attempt to identify these modes in a semiagnostic way, without imposing priors on the source of the perturbation. This is usually known as black-hole spectroscopy. Applying this framework to GW150914, the measurement of the first overtone led to the confirmation of the theorem to 20% level. We show, however, that such semiagnostic tests cannot provide strong evidence in favor of the no-hair theorem, even for extremely loud signals, given the increasing number of overtones (and free parameters) needed to fit the data. This can be solved by imposing prior assumptions on the origin of the perturbed black hole that can further constrain the explored parameters: in particular, our knowledge that the ringdown is sourced by a binary black-hole merger. Applying this strategy to GW150914, we find a natural log Bayes factor of ∼6.5 in favor of the Kerr nature of its remnant, indicating that the hairy object hypothesis is disfavored with <1:600 with respect to the Kerr black-hole one.
The sensitivity of gravitational wave searches for binary black holes is estimated via the injection and posterior recovery of simulated gravitational wave signals in the detector data streams. When ...a search reports no detections, the estimated sensitivity is then used to place upper limits on the coalescence rate of the target source. In order to obtain correct sensitivity and rate estimates, the injected waveforms must be faithful representations of the real signals. Up to date, however, injected waveforms have neglected radiation modes of order higher than the quadrupole, potentially biasing sensitivity and coalescence rate estimates. In particular, higher-order modes are known to have a large impact in the gravitational waves emitted by intermediate-mass black holes binaries. In this work, we evaluate the impact of this approximation in the context of two search algorithms run by the LIGO Scientific Collaboration in their search for intermediate-mass black hole binaries in the O1 LIGO Science Run data: a matched filter–based pipeline and a coherent unmodeled one. To this end, we estimate the sensitivity of both searches to simulated signals for nonspinning binaries including and omitting higher-order modes. We find that omission of higher-order modes leads to biases in the sensitivity estimates which depend on the masses of the binary, the search algorithm, and the required level of significance for detection. In addition, we compare the sensitivity of the two search algorithms across the studied parameter space. We conclude that the most recent LIGO-Virgo upper limits on the rate of coalescence of intermediate-mass black hole binaries are conservative for the case of highly asymmetric binaries. However, the tightest upper limits, placed for nearly equal-mass sources, remain unchanged due to the small contribution of higher modes to the corresponding sources.
We report a degeneracy between the gravitational-wave signals from quasicircular precessing black-hole mergers and those from extremely eccentric mergers, namely, head-on collisions. Performing model ...selection on numerically simulated signals of head-on collisions using models for quasicircular binaries, we find that, for signal-to-noise ratios of 15 and 25, typical of Advanced LIGO observations, head-on mergers with respective total masses of M ∈ ( 125 , 300 ) M ⊙ and M ∈ ( 200 , 440 ) M ⊙ would be identified as precessing quasicircular intermediate-mass black-hole binaries located at a much larger distance. Ruling out the head-on scenario would require us to perform model selection using currently nonexistent waveform models for head-on collisions, together with the application of astrophysically motivated priors on the (rare) occurrence of those events. We show that in situations where standard parameter inference of compact binaries may report component masses inside (outside) the pair-instability supernova gap, the true object may be a head-on merger with masses outside (inside) this gap. We briefly discuss the potential implications of these findings for GW190521, which we analyze in detail in J. Calderón Bustillo et al., Phys. Rev. Lett. 126, 081101 (2021).
The advent of gravitational wave (GW) astronomy has provided us with observations of black holes more massive than those known from x-ray astronomy. However, the observation of an intermediate-mass ...black hole (IMBH) remains a big challenge. After their second observing run, the LIGO & Virgo Scientific collaborations (LVC) placed upper limits on the coalescence rate density of nonprecessing IMBH binaries (IMBHBs). In this Numerical Relativity Injection Analysis (NuRIA), we explore the sensitivity of two of the search pipelines used by the LVC to signals from 69 numerically simulated IMBHBs with total mass greater than 200 M ⊙ having generic spins, out of which 27 have a precessing orbital plane. In particular, we compare the matched-filter search PyCBC, and the coherent model-independent search technique cWB. We find that, in general, cWB is more sensitive to IMBHBs than PyCBC, with the difference in sensitivity depending on the masses and spins of the source. Consequently, we use cWB to place the first upper limits on the merger rate of generically spinning IMBH binaries using publicly available data from the first Advanced LIGO observing run.
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