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On the formation of GW190814

Lu, Wenbin and Beniamini, Paz and Bonnerot, Clément (2021) On the formation of GW190814. Monthly Notices of the Royal Astronomical Society, 500 (2). pp. 1817-1832. ISSN 0035-8711.

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The LIGO–Virgo collaboration recently reported a puzzling event, GW190814, with component masses of 23 and 2.6 M_⊙. Motivated by the relatively small rate of such a coalescence (1–23 Gpc⁻³ yr⁻¹) and the fact that the mass of the secondary is close to the total mass of known binary neutron star (bNS) systems, we propose that GW190814 was a second-generation merger from a hierarchical triple system; i.e. the remnant from the bNS coalescence was able to merge again with the 23 M_⊙ black hole (BH) tertiary. We show that this occurs at a sufficiently high probability provided that the semimajor axis of the outer orbit is less than a few au at the time of bNS coalescence. It remains to be explored whether the conditions for the formation of such tight triple systems are commonly realized in the Universe, especially in low-metallicity (≲0.1 Z⊙) environments. Our model provides a number of predictions. (1) The spin of the secondary in GW190814-like systems is 0.6–0.7. (2) The component mass distribution from a large sample of LIGO sources should have a narrow peak between 2.5 and ∼3.5 M_⊙, whereas the range between ∼3.5 and ∼5 M⊙ stays empty (provided that stellar evolution does not generate such BHs in the ‘mass gap’). (3) About 90 per cent (10 per cent) of GW190814-like events have an eccentricity of e ≳ 2 × 10⁻³ (≳0.1) near gravitational wave frequency of 10 mHz. (4) A significant fraction (⁠≳10 percent⁠) of bNS mergers should have signatures of a massive tertiary at a distance of a few au in the gravitational waveform. (5) There are 10⁵ undetected radio-quiet bNS systems with a massive BH tertiary in the Milky Way.

Item Type:Article
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URLURL TypeDescription Paper
Lu, Wenbin0000-0002-1568-7461
Beniamini, Paz0000-0001-7833-1043
Bonnerot, Clément0000-0001-9970-2843
Additional Information:© 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 October 21. Received 2020 October 4; in original form 2020 September 10. Published: 02 November 2020. WL thank Shri Kulkarni for his encouragement throughout this project and many insightful suggestions. We thank Tony Piro for suggesting looking into low-GW-frequency observations of the predicted signals. We thank Brian Metzger, Bin Liu, Imre Bartos, Kyle Kremer, Jim Fuller, Ylva Goetberg, and Pawan Kumar for many useful discussions and comments. We acknowledge the detailed explanations of their earlier work on AGN-assisted mergers by Imre Bartos and Yang Yang. WL was supported by the David and Ellen Lee Fellowship at Caltech. The research of PB and CB was funded by the Gordon and Betty Moore Foundation through grant GBMF5076. Data Availability: The data underlying this article will be shared on reasonable request to the corresponding author.
Funding AgencyGrant Number
David and Ellen Lee Postdoctoral ScholarshipUNSPECIFIED
Gordon and Betty Moore FoundationGBMF5076
Subject Keywords:gravitational waves – black holes – stars: neutron
Issue or Number:2
Record Number:CaltechAUTHORS:20201012-142717744
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Official Citation:Wenbin Lu, Paz Beniamini, Clément Bonnerot, On the formation of GW190814, Monthly Notices of the Royal Astronomical Society, Volume 500, Issue 2, January 2021, Pages 1817–1832,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105990
Deposited By: Tony Diaz
Deposited On:12 Oct 2020 21:41
Last Modified:04 Feb 2021 22:27

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