Signs of eccentricity in two gravitational-wave signals may indicate a sub-population of dynamically assembled binary black holes

Romero-Shaw, Isobel M.; Lasky, Paul D.; Thrane, Eric

doi:10.48550/arxiv.2108.01284

“…References[82,83] also discuss possible correlations between the eccentricity and the effective spin parameter χ eff . While we do not investigate this in our MCMC analysis here, Fig.11in Appendix C shows a weak correlation between e 0 and the individual spin parameters χ i in our Fisher matrix analysis.…”

mentioning

confidence: 99%

Constraining the orbital eccentricity of inspiralling compact binary systems with Advanced LIGO

Favata,

Kim,

Arun

et al. 2021

Preprint

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The detection of ∼ 50 coalescing compact binaries with the Advanced LIGO and Virgo detectors has allowed us to test general relativity, constrain merger rates, and look for evidence of tidal effects, compact object spins, higher waveform modes, and black hole ringdowns. An effect that has not yet been confidently detected is binary eccentricity, which might be present in a small fraction of binaries formed dynamically. Here we discuss general limits on eccentricity that can, in-principle, be placed on all types of compact object binaries by a detector operating at the design sensitivity of Advanced LIGO. Using a post-Newtonian model for gravitational-wave phasing valid in the small eccentricity regime, we assess the relative measurement error for eccentricity for a variety of spinning and non-spinning binaries. Errors and correlations involving the mass and spin parameters are also investigated. We find that decreasing the low frequency limit of a detector's observational frequency band is one of the key design factors for increasing the odds of measuring binary eccentricity. We also introduce and analytically explore the eccentric chirp mass parameter, which replaces the chirp mass as the key measurable parameter combination in eccentric gravitational waveform models. The eccentric chirp mass parameter explains a degeneracy between the chirp mass and the eccentricity. This degeneracy leads to a bias in the standard chirp mass parameter. We also investigate the systematic parameter bias that arises when eccentric systems are recovered using circular waveform templates. We use both Fisher matrix and Bayesian-inference-based Markov Chain Monte Carlo (MCMC) methods to investigate these parameter estimation issues, and we find good agreement between the two approaches (for both statistical and systematic errors) in the appropriate signal-to-noise ratio regime. This study helps to quantify how effectively one can use eccentricity measurements as a probe of binary formation channels.

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“…More recently, Ref. [83] analyzed 36 of the BBHs in GWTC-2 [12] using Bilby and assuming aligned spins. Making use of the waveform model in [74], they find twelve events with some support for eccentricity e 0 ≥ 0.05.…”

Section: Searches and Parameter Estimation Constraints For Eccentric ...mentioning

confidence: 99%

Constraining the orbital eccentricity of inspiralling compact binary systems with Advanced LIGO

Favata

¹

,

Kim

²

,

Arun

³

et al. 2022

View full text Add to dashboard Cite

The detection of ∼ 50 coalescing compact binaries with the Advanced LIGO and Virgo detectors has allowed us to test general relativity, constrain merger rates, and look for evidence of tidal effects, compact object spins, higher waveform modes, and black hole ringdowns. An effect that has not yet been confidently detected is binary eccentricity, which might be present in a small fraction of binaries formed dynamically. Here we discuss general limits on eccentricity that can, in-principle, be placed on all types of compact object binaries by a detector operating at the design sensitivity of Advanced LIGO. Using a post-Newtonian model for gravitational-wave phasing valid in the small eccentricity regime, we assess the relative measurement error for eccentricity for a variety of spinning and non-spinning binaries. Errors and correlations involving the mass and spin parameters are also investigated. We find that decreasing the low frequency limit of a detector's observational frequency band is one of the key design factors for increasing the odds of measuring binary eccentricity. We also introduce and analytically explore the eccentric chirp mass parameter, which replaces the chirp mass as the key measurable parameter combination in eccentric gravitational waveform models. The eccentric chirp mass parameter explains a degeneracy between the chirp mass and the eccentricity. This degeneracy leads to a bias in the standard chirp mass parameter. We also investigate the systematic parameter bias that arises when eccentric systems are recovered using circular waveform templates. We use both Fisher matrix and Bayesian-inference-based Markov Chain Monte Carlo (MCMC) methods to investigate these parameter estimation issues, and we find good agreement between the two approaches (for both statistical and systematic errors) in the appropriate signal-to-noise ratio regime. This study helps to quantify how effectively one can use eccentricity measurements as a probe of binary formation channels.

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“…Work in [49] estimated that ∼ 4% of the binary black holes (BBHs) detectable from clusters will have measurable eccentricity. Recent claims have indicated signatures of (or constraints on) binary eccentricity in observed GW events, suggesting a subpopulation of dynamically formed binaries [50][51][52][53]. See Sec.…”

Section: Introductionmentioning

confidence: 97%

Systematic bias on parameterized tests of general relativity due to neglect of orbital eccentricity

Saini¹,

Favata²,

Arun³

2022

Preprint

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Gravitational-wave observations provide a unique opportunity to test General Relativity (GR) in the strong-field and highly-dynamical regime of the theory. Parameterized tests of GR are one well-known approach for quantifying violations of GR. This approach constrains deviations in the coefficients of the post-Newtonian (PN) phasing formula, which describes the gravitational-wave phase evolution of a compact binary as it inspirals. Current bounds from this test using LIGO/Virgo observations assume that binaries are circularized by the time they enter the detector frequency band. Here, we investigate the impact of residual binary eccentricity on the parameterized tests. We study the systematic biases in the parameter bounds when a phasing based on the circular orbit assumption is employed for a system that has some small residual eccentricity. We find that a systematic bias (for example, on the leading Newtonian deformation parameter) becomes comparable to the statistical errors for even moderate eccentricities of ∼ 0.04 at 10 Hz in LIGO/Virgo band. This happens at an even lower value of orbital eccentricity (∼ 0.005 at 10 Hz) in the frequency band of third-generation (3G) detectors like Cosmic Explorer. These results demonstrate that incorporating physical effects like eccentricity in waveform models is important for accurately extracting science results from future detectors.

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Signs of eccentricity in two gravitational-wave signals may indicate a sub-population of dynamically assembled binary black holes

Cited by 5 publications

References 94 publications

Constraining the orbital eccentricity of inspiralling compact binary systems with Advanced LIGO

Constraining the orbital eccentricity of inspiralling compact binary systems with Advanced LIGO

Constraining the orbital eccentricity of inspiralling compact binary systems with Advanced LIGO

Systematic bias on parameterized tests of general relativity due to neglect of orbital eccentricity

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