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Search for gravitational waves from eccentric binary black holes with an effective-one-body template

Yi-Fan Wang, Alexander H. Nitz

TL;DR

This work tackles the challenge of detecting gravitational waves from eccentric binary black holes by introducing the first matched-filtering search that uses an eccentric effective-one-body waveform (SEOBNRv5EHM) to cover $m_1,m_2\in[5,200]\,M_\odot$ and $e_{20Hz}\le 0.5$ in LVK O3 data. A large stochastic template bank (~860k templates) spanning six intrinsic parameters is constructed, and a PyCBC-based pipeline with standard signal-consistency tests and a glitch-aware ranking statistic is applied, yielding 28 significant events with FAR < 1/100 yr and 16 additional candidates. While some detections align with previous catalogs and eccentricity claims, no unambiguous eccentric BBH is established; nonetheless, the analysis provides the most stringent upper limits to date on the event-rate density of eccentric BBH in the 5–30 $M_\odot$ range, e.g., $R_{90}<0.06\ \mathrm{Gpc^{-3}\,yr^{-1}}$ for a 30–30 $M_\odot$ system with $e_{20Hz}=0.5$, corresponding to a sensitive distance of about $2.4$ Gpc and an approximately eightfold increase in sensitive volume over prior searches. This demonstrates the feasibility of eccentric-template matched filtering and lays groundwork for future improvements, such as incorporating higher-order modes and refining noise mitigation, which will be crucial for the O4 run and next-generation detectors.

Abstract

As gravitational wave astronomy has entered an era of routine detections, it becomes increasingly important to precisely measure the physical parameters of individual events and infer population properties. Eccentricity is a key observable, suggesting that binaries form in a dense stellar environment through dynamical encounters. This work performs the first matched-filtering search for gravitational waves from eccentric binary black holes (BBHs) covering the mass range $[5, 200]~M_\odot$ and eccentricity at 20 Hz up to 0.5 with a newly developed effective-one-body waveform model. Throughout the third observation run of LIGO, Virgo, and KAGRA, we identify 28 BBH events with a false alarm rate below once per 100 yr; all of which were previously reported in the GWTC-3 and 4-OGC catalogs. Additional candidates with false alarm rates between once per 1 and 100 yr are also reported. We perform an injection campaign to characterize the sensitive volume time of our search pipeline. Assuming that none of the eccentric BBH events were missed by previous searches, our results provide constraints on the event rate of eccentric BBHs in the mass range [5, 30] $M_\odot$. For a 30-30 $M_\odot$ BBH with eccentricity 0.5, the event rate is limited to less than 0.06 Gpc$^{-3}$ yr$^{-1}$; this marks an order of magnitude improvement for sensitive volume compared with the previous search with a minimally modeled algorithm without using templates.

Search for gravitational waves from eccentric binary black holes with an effective-one-body template

TL;DR

This work tackles the challenge of detecting gravitational waves from eccentric binary black holes by introducing the first matched-filtering search that uses an eccentric effective-one-body waveform (SEOBNRv5EHM) to cover and in LVK O3 data. A large stochastic template bank (~860k templates) spanning six intrinsic parameters is constructed, and a PyCBC-based pipeline with standard signal-consistency tests and a glitch-aware ranking statistic is applied, yielding 28 significant events with FAR < 1/100 yr and 16 additional candidates. While some detections align with previous catalogs and eccentricity claims, no unambiguous eccentric BBH is established; nonetheless, the analysis provides the most stringent upper limits to date on the event-rate density of eccentric BBH in the 5–30 range, e.g., for a 30–30 system with , corresponding to a sensitive distance of about Gpc and an approximately eightfold increase in sensitive volume over prior searches. This demonstrates the feasibility of eccentric-template matched filtering and lays groundwork for future improvements, such as incorporating higher-order modes and refining noise mitigation, which will be crucial for the O4 run and next-generation detectors.

Abstract

As gravitational wave astronomy has entered an era of routine detections, it becomes increasingly important to precisely measure the physical parameters of individual events and infer population properties. Eccentricity is a key observable, suggesting that binaries form in a dense stellar environment through dynamical encounters. This work performs the first matched-filtering search for gravitational waves from eccentric binary black holes (BBHs) covering the mass range and eccentricity at 20 Hz up to 0.5 with a newly developed effective-one-body waveform model. Throughout the third observation run of LIGO, Virgo, and KAGRA, we identify 28 BBH events with a false alarm rate below once per 100 yr; all of which were previously reported in the GWTC-3 and 4-OGC catalogs. Additional candidates with false alarm rates between once per 1 and 100 yr are also reported. We perform an injection campaign to characterize the sensitive volume time of our search pipeline. Assuming that none of the eccentric BBH events were missed by previous searches, our results provide constraints on the event rate of eccentric BBHs in the mass range [5, 30] . For a 30-30 BBH with eccentricity 0.5, the event rate is limited to less than 0.06 Gpc yr; this marks an order of magnitude improvement for sensitive volume compared with the previous search with a minimally modeled algorithm without using templates.

Paper Structure

This paper contains 7 sections, 7 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Search parameter space
  3. Search strategy
  4. Results
  5. Astrophysical event rate
  6. Conclusion
  7. Data quality checks around 190805_112555

Figures (5)

  • Figure 1: This plot showcases the morphology of the GW plus polarization from a 30-30 $\mathrm{M}_{\odot}$, zero spin BBH system generated by SEOBNRv5E. The initial eccentricity at 20 Hz is chose to be 0 (labeled as "quasi-circular"), 0.3 and 0.5 respectively. For $e_\mathrm{20Hz}$ = 0.5, two cases of the initial relativistic anomaly with $\zeta= 0$ or $\pi$ are presented. The dashed lines present the amplitude of the combined polarization $h_+ - ih_\times$.
  • Figure 2: The parameter space of the template bank of this work. In comparison, we also plot the search region of Ref. Dhurkunde:2023qoe for binaries with neutron stars and Nitz:2022ltl for binaries with at least one subsolar mass component. We also plot a region from the minimally modeled search by LVK without using a template LIGOScientific:2023lpe. Note that this region is where the sensitivity is reported by Ref. LIGOScientific:2023lpe.
  • Figure 3: The mismatch, which is 1 - fitting factor, comparison between an injection of simulations generated using SEOBNRv5E with only $(2,\pm2)$ mode. We also present the results by using all available higher modes with $(2,\pm2), (2,\pm1), (3,\pm3), (3,\pm2), (4,\pm4$), and $(4,\pm3)$ with SEOBNRv5EHM.
  • Figure 4: The 90% upper limit for the event rate density, $R_\mathrm{90}$, for a population of eccentric BBH with discrete source parameters.
  • Figure 5: In the first row, we plot the matched-filtering SNR (defined in \ref{['eq:snr']} with the observed data from LIGO Hanford and LIGO Livingston, and the residual data subtracting the best matched templates from matched-filtering. The SNR time series peak no longer exists in the residual data. The middle rows represent the constant-Q short-time Fourier transformation of the observed data, overplotted by white dashed lines for the frequency-time evolution of the best-matched templates, which is consistent with an eccentric BBH with component masses 69 and 15.8 $\mathrm{M}_{\odot}$, component spin $s_{1z}$ and $s_{2z}$ being 0.5 and 0.22, respectively, and an eccentricity at 20 Hz of 0.47. The last row presents the constant-Q transformation with the residual data by subtracting the best-matched template.