Black hole mergers induced by tidal encounters with a galactic centre black hole

Abstract

We discuss the properties of stellar mass black hole (BH) mergers induced by tidal encounters with a massive BH at galactic centres or potentially in dense star clusters. The tidal disruption of stellar binaries by a massive BH is known to produce hypervelocity stars. However, such a tidal encounter does not always lead to the break-up of binaries. Since surviving binaries tend to become hard and eccentric, this process can produce BH mergers in principle. For initially circular binaries, we show that the gravitational wave (GW) merger times become shorter by a factor of more than 10 2 (10 5 ) in 10% (1%) of the surviving cases. We also investigate the effective spins of the survivors, assuming that BH spins are initially aligned with the binary orbital angular momentum. We find that binary orientations can flip in the opposite direction at the tidal encounter. For the survivors with large merger time reduction factors, the effective spin distribution is rather flat. The current and near-future GW observatories are expected to detect an enormous number of BH mergers. If mergers are found in the vicinity of massive BHs (e.g. the detection of GW lensing echoes), this tidal mechanism would provide a possible explanation for their origin. We also discuss whether the moment of the tidal encounter can be observed by low frequency GW detectors (e.g. LISA, DECIGO, BBO, MAGIS, ALIA). Binaries emitting GW at > ∼ 6 × 10 −3 Hz would be swallowed by 4 × 10 6 M ⊙ BHs without tidal disruption.

Exploring compact binary merger host galaxies and environments with $\rm{zELDA}$

“…Compact binaries may also form through dynamical channels (e.g. Rodriguez et al 2015Rodriguez et al , 2016Rodriguez & Loeb 2018;Fragione & Kocsis 2018;Samsing & D'Orazio 2018;Choksi et al 2019;Fernández & Kobayashi 2019;Andrews & Mandel 2019) merger rate of such binaries has been estimated to be small when compared to isolated binaries (Belczynski et al 2018;Ye et al 2019).…”

Fingerprints of Binary Black Hole Formation Channels Encoded in the Mass and Spin of Merger Remnants

“…These second generation BHs can significantly affect the BH mass spectrum. In galactic nuclei, BBH evolution and coalescence is even more complex due to the possible presence of a quiescent SMBH (Antonini & Perets 2012;Arca Sedda & Gualandris 2018;Hoang et al 2018;Arca Sedda & Capuzzo-Dolcetta 2019;Fernández & Kobayashi 2019;Hoang et al 2019;Rasskazov & Kocsis 2019) or an AGN in the galactic center (Bartos et al 2017;Yang et al 2019).…”

Neutron Star–Black Hole Mergers from Gravitational-wave Captures

“…) and BNSs (110-3840 --Gpc yr 3 1 ) (Abbott et al 2019b). A very diverse range of mechanisms and astrophysical environments have been invoked to explain these mergers, such as dynamical interactions in globular clusters (GCs; e.g., Portegies Zwart & McMillan 2000;Wen 2003;O'Leary et al 2006O'Leary et al , 2016Antonini et al 2014;Rodriguez et al 2016;Kremer et al 2020b;Samsing et al 2020) and galactic nuclei (GN; e.g., O'Leary et al 2009;Antonini & Perets 2012;Kocsis & Levin 2012;Ramirez-Ruiz et al 2015;Hoang et al 2018;Fernández & Kobayashi 2019), active galactic nuclei (e.g., McKernan et al 2012;Bartos et al 2017;Stone et al 2017;Secunda et al 2019), isolated binary evolution in the field (e.g., Belczynski et al 2016;Marchant et al 2016), Population III stars (e.g., Kinugawa et al 2014Kinugawa et al , 2016Dvorkin et al 2016;Hartwig et al 2016;Inayoshi et al 2016), and primordial black holes (e.g., Bird et al 2016;Sasaki et al 2016;Clesse & García-Bellido 2017).…”