Greatly Enhanced Merger Rates of Compact-object Binaries in Non-spherical Nuclear Star Clusters

By C. Petrovich, F. Antonini. 2017

137 citations recorded by the source corpus.

The Milky Way and a significant fraction of galaxies are observed to host a central massive black hole (MBH) embedded in a non-spherical nuclear star cluster. We study the secular orbital evolution of compact-object binaries in these environments and characterize the excitation of extremely large eccentricities that can lead to mergers by gravitational radiation. We find that the eccentricity excitation occurs most efficiently when the nodal precession timescale of the binary’s orbit around the MBH due to the non-spherical cluster becomes comparable (within a factor of ∼10) to the timescale on which the binary is torqued by the MBH due to the Lidov–Kozai (LK) mechanism. We show that in this regime the perturbations due to the cluster increase the fraction of systems that reach extreme eccentricities ( ) by a factor of ∼10–100 compared to the idealized case of a spherical cluster, increasing the merger rates of compact objects by a similar factor. We identify two main channels that lead to this extreme eccentricity excitation: (i) chaotic diffusion of the eccentricities due to resonance overlap; (ii) cluster-driven variations of the mutual inclinations between the binary orbit and its center-of-mass orbit around the MBH, which can intensify the LK oscillations. We estimate that our mechanism can produce BH–BH and BH–neutron star binary merger rates of up to and , respectively. Thus, we propose the cluster-enhanced LK mechanism as a new channel for the merger of compact-object binaries, competing with scenarios that invoke isolated binary evolution or dynamical formation in globular clusters.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/eea63f0f0a5429183a95818a63996bc698786c78

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In Astronomy and Astrophysics

1. Michela Mapelli
2. N. Giacobbo
3. F. Antonini
4. Ilya Mandel
5. D. Holz
6. Mario Spera
7. F. Rasio
8. B. Kocsis

Citations in the corpus

• Double neutron stars: merger rates revisited (2017, background): “…] 1 7 O ct binary components, and dynamical - occurring in dense environments, where the dynamical interactions between stars are important e.g. in globular clusters or nuclear clusters (e.g. Phinney 1996; Grindlay, Portegies Zwart & McMillan 2006; Ivanova et al. 2008; Petrovich & Antonini 2017).”
• Black Hole Mergers in Galactic Nuclei Induced by the Eccentric Kozai–Lidov Effect (2017, methodology): “First, one should differentiate between Newtonian precession that occurs due to a spherical mass distribution (which was what we assumed in the paper), versus precession due to deviations from spherical symmetry as explored in Petrovich & Antonini (2017).”
• On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening (2017, background): “…is the same, including the numbers of BHBs, their orbital parameters, the encounter rate, the age of the stellar population(s), etc. Interestingly, Petrovich & Antonini (2017) also found that non-spherical clusters can enhance the rates of BH-BH binary mergers relative to spherical clusters, but…”
• Black hole and neutron star mergers in galactic nuclei (2018, background): “The in-plane precession induced by the nuclear cluster potential and departures from spherical symmetry in the galactic nucleus would make the CO center of mass orbit precess even faster than is quantified by vector resonant relaxation alone in a MW-like nucleus (Petrovich & Antonini 2017).”
• Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo (2018, background): “…2016a; Mapelli 2016; Askar et al. 2017; Banerjee 2017; Chatterjee et al. 2017) and galactic nuclei (Antonini & Perets 2012; Antonini & Rasio 2016; Petrovich & Antonini 2017), evolution of hierarchical triple systems(Antonini et al. 2014, 2017; Kimpson et al. 2016; Liu & Lai 2018), gas drag and…”
• Black hole growth through hierarchical black hole mergers in dense star clusters: implications for gravitational wave detections (2018, background): “Including the contribution from NCs hosting a massive BH could increase these rates significantly (O’Leary et al. 2009; Antonini & Perets 2012; VanLandingham et al. 2016; Petrovich & Antonini 2017; Hamers et al. 2018).”
• The spin of the second-born black hole in coalescing binary black holes (2018, background): “…Marchant et al. 2016; Mandel & de Mink 2016; Song et al. 2016), and (ii) dynamical formation in globular clusters (Sigurdsson & Hernquist 1993; Rodriguez et al. 2015, 2016) and galactic nuclear clusters (Miller & Lauburg 2009; O’Leary et al. 2009; Kocsis & Levin 2012; Petrovich & Antonini 2017).”
• The progenitors of compact-object binaries: impact of metallicity, common envelope and natal kicks (2018, background): “…Colpi et al. 2003; Mapelli et al. 2005; Grindlay et al. 2006; Ivanova et al. 2008; Clausen et al. 2013; Mapelli & Zampieri 2014; Ziosi et al. 2014; Rodriguez et al. 2015, 2016; Mapelli 2016; Askar et al. 2016; Antonini et al. 2017; Petrovich & Antonini 2017; Banerjee 2017; Belczynski et al. 2017a).”
• Eccentric Black Hole Gravitational-wave Capture Sources in Galactic Nuclei: Distribution of Binary Parameters (2017, methodology): “BH binaries in orbit around a supermassive BH (SMBH) in galactic nuclei (GNs) also represent hierarchical triples (Antonini & Perets 2012; VanLandingham et al. 2016; Petrovich & Antonini 2017; Hoang et al. 2018; Randall & Xianyu 2018a, 2018b).”