Merging Black Hole Binaries in Galactic Nuclei: Implications for Advanced-Ligo Detections

Abstract

Motivated by the recent detection of gravitational waves from the black hole binary merger GW150914, we study the dynamical evolution of (stellar mass) black holes in galactic nuclei where massive star clusters reside. With masses of ∼ 10 7 M and sizes of only a few parsecs, nuclear star clusters are the densest stellar systems observed in the local universe and represent a robust environment where black hole binaries can dynamically form, harden and merge. We show that due to their large escape speeds, nuclear star clusters can retain a large fraction of their merger remnants. Successive mergers can then lead to significant growth and produce black hole mergers of several tens of solar masses similar to GW150914 and up to a few hundreds of solar masses, without the need of invoking extremely low metallicity environments. We use a semi-analytical approach to describe the dynamics of black holes in massive star clusters. Our models give a black hole binary merger rate of ≈ 1.5 Gpc −3 yr −1 from nuclear star clusters, implying up to a few tens of possible detections per year with Advanced LIGO. Moreover, we find a local merger rate of ∼ 1 Gpc −3 yr −1 for high mass black hole binaries similar to GW150914; a merger rate comparable to that of similar binaries assembled dynamically in globular clusters. Finally, we show that if all black holes receive high natal kicks, 50 km s −1 , then nuclear star clusters will dominate the local merger rate of binary black holes compared to either globular clusters or isolated binary evolution.

Multi-band gravitational wave astronomy: science with joint space- and ground-based observations of black hole binaries

“…BHBs can in fact originate from a variety of astrophysical channels, including: standard evolution of field massive stellar binaries [5], dynamical formation in dense stellar clusters [6] or in dense compact remnant cusps surrounding nuclear massive black holes [7], evolution of chemically mixed massive binaries [8], population III remnants [9], primordial black holes [10]. Every channel, however, is subject to considerable uncertainties.…”

Spin–Orbit Misalignment of Merging Black Hole Binaries with Tertiary Companions

“…Such triple BH systems could be a direct product of massive triple stars in the galactic field (Silsbee & Tremaine 2017;Antonini et al 2017), or could be produced dynamically in a dense cluster (Miller & Hamilton 2002;Rodriguez et al 2015;Antonini & Rasio 2016). For binaries formed near the center of a galaxy, the third body could be a supermassive BH (Antonini & Perets 2012;Petrovich & Antonini 2017).…”

Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution

“…Binary BHs can form as the result of: (i) the evolution of isolated massive binaries in galactic fields (Belczynski et al 2010(Belczynski et al , 2016Mandel & de Mink 2016); (ii) dynamical interactions in galactic nuclei, with and without a massive BH (Antonini & Perets 2012;Antonini & Rasio 2016); (iii) dynamical exchange interactions in the dense stellar core of globular clusters (Rodriguez et al 2015;Haster et al 2016;Chatterjee et al 2017) or young massive star clusters (Banerjee 2017); (iv) the evolution of isolated triples in galactic fields (Silsbee & Tremaine 2016), leading to a merger of the inner binary through the Lidov-Kozai mechanism (LK;Lidov 1962;Kozai 1962) coupled with energy loss due to GW radiation (e.g., Thompson 2011;Antonini et al 2014;Kimpson et al 2016).…”