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Eccentricity estimate for black hole mergers with numerical relativity simulations

Abstract

The origin of black hole mergers discovered by the LIGO1 and Virgo2 gravitational-wave observatories is currently unknown. GW1905213,4 is the heaviest black hole merger detected so far. Its observed high mass and possible spin-induced orbital precession could arise from the binary having formed following a close encounter. An observational signature of close encounters is eccentric binary orbit5,6,7; however, this feature is currently difficult to identify due to the lack of suitable gravitational waveforms. No eccentric merger has been previously found8. Here we report 611 numerical relativity simulations covering the full eccentricity range and an estimation approach to probe the eccentricity of mergers. Our set of simulations corresponds to ~105 waveforms, comparable to the number used in gravitational-wave searches, albeit with coarser mass ratio and spin resolution. We applied our approach to GW190521 and found that it is most consistent with a highly eccentric (\(e=0.6{9}_{-0.22}^{+0.17}\); 90% credible level) merger within our set of waveforms. This interpretation is supported over a non-eccentric merger with >10 odds ratio if 10% of GW190521-like mergers are highly eccentric. Detectable orbital eccentricity would be evidence against an isolated binary origin, which is otherwise difficult to rule out on the basis of observed mass and spin9,10.

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Fig. 1: Marginalized likelihood as a function of eccentricity for our numerical relativity simulations explaining GW190521.
Fig. 2: Reconstructed waveform of GW190521 and consistency test.

Data availability

Numerical relativity waveforms generated for and used in this study will be accessible at http://ccrg.rit.edu/~RITCatalog. Data generated by our calculations are available in Supplementary Information or are available from the corresponding authors upon reasonable request.

Code availability

The computer code that was used for the calculations is available from the corresponding authors upon reasonable request.

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Acknowledgements

We thank C. Belczynski, E. Katsavounidis, A. Loeb and S. Vitale for useful suggestions, and G. Vedovato for his valuable help with the cWB search algorithm and with the set-up of the cWB waveform consistency study. We gratefully acknowledge the US National Science Foundation (NSF) for financial support from grants PHY-1912632 (C.O.L., M.C., R.O.), PHY-1911796 (I.B.), PHY-1806165 (S.K.), PHY-1707946 (M.C.), ACI-1550436 (M.C.), AST-1516150 (M.C.), ACI-1516125 (M.C.), PHY-1726215 (M.C., C.O.L.), NASA TCAN grant 80NSSC18K1488 (M.C., R.O.), and the support of the Alfred P. Sloan Foundation (I.B.). This work used the Extreme Science and Engineering Discovery Environment (XSEDE) (allocation TG-PHY060027N), which is supported by NSF grant ACI-1548562 and Frontera projects PHY-20010 and PHY-20007. Computational resources were also provided by NewHorizons, BlueSky Clusters and Green Prairies at the Rochester Institute of Technology, which were supported by NSF grants PHY-0722703 (M.C., C.O.L.), DMS-0820923, AST-1028087 (M.C.), PHY-1229173 (M.C., C.O.L.) and PHY-1726215 (M.C., C.O.L.). We are grateful for computational resources provided by the Leonard E. Parker Center for Gravitation, Cosmology and Astrophysics at the University of Wisconsin—Milwaukee supported by NSF grant PHY-1626190. We also acknowledge the use of IUCAA LDG cluster Sarathi for the computational/numerical work. We also acknowledge the use of LDG clusters at CIT, LHO and LLO for the computational/numerical work. This research has made use of data, software and/or web tools obtained from the Gravitational Wave Open Science Center (https://www.gw-openscience.org), a service of LIGO Laboratory, the LIGO Scientific Collaboration and the Virgo Collaboration. LIGO is funded by the NSF. Virgo is funded by the French Centre National de Recherche Scientifique (CNRS), the Italian Istituto Nazionale della Fisica Nucleare (INFN) and the Dutch Nikhef, with contributions by Polish and Hungarian institutes.

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Contributions

I.B and R.O. contributed to the origination of the idea. J.H., J.L., C.O.L., M.C. and R.O. carried out the numerical relativity simulations and the Rochester Institute of Technology sensitivity studies. V.G., B.O., M.S., S.K. and I.B. carried out the cWB consistency check. All authors worked out collaboratively the general details of the project. V.G. created the figures with input from all other authors. All authors helped edit the manuscript.

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Correspondence to Imre Bartos or R. O’Shaughnessy.

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Nature Astronomy thanks Maya Fishbach and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–6 and Tables 1–3.

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Gayathri, V., Healy, J., Lange, J. et al. Eccentricity estimate for black hole mergers with numerical relativity simulations. Nat Astron 6, 344–349 (2022). https://doi.org/10.1038/s41550-021-01568-w

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