Dynamics of triple black hole systems in hierarchically merging massive galaxies

By Loren Hoffman, Abraham Loeb. 2006

138 citations recorded by the source corpus.

Galaxies with stellar bulges are generically observed to host supermassive black holes (SMBHs). The hierarchical merging of galaxies should therefore lead to the formation of SMBH binaries. Merging of old massive galaxies with little gas promotes the formation of low-density nuclei where SMBH binaries are expected to survive over long times. If the binary lifetime exceeds the typical time between mergers, then triple black hole (BH) systems may form. We study the statistics of close triple SMBH encounters in galactic nuclei by computing a series of three-body orbits with physically motivated initial conditions appropriate for giant elliptical galaxies. Our simulations include a smooth background potential consisting of a stellar bulge plus a dark matter halo, drag forces due to gravitational radiation and dynamical friction on the stars and dark matter, and a simple model of the time evolution of the inner density profile under heating and mass ejection by the SMBHs. We find that the binary pair coalesces as a result of repeated close encounters in ∼85 per cent of our runs, and in ∼15 per cent of cases a new eccentric binary forms from the third SMBH and binary remnant and coalesces during the run time. In about 40 per cent of the runs the lightest BH is left wandering through the galactic halo or escapes the galaxy altogether, but escape of all three SMBHs is exceedingly rare. The triple systems typically scour out cores with mass deficits ∼one‐two times their total mass, which can help to account for the large cores observed in some massive elliptical galaxies, such as M87. The high coalescence rate, prevalence of very high-eccentricity orbits, and gravitational radiation ‘spikes’ during close encounters in our runs, may provide interesting signals for the future Laser Interferometer Space Antenna (LISA).

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/46630ec526a664ef6fb512855cafdd3aea313ec8

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Citations in the corpus

The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational-wave Background (2023, background): “Triple SMBH interactions can greatly reduce the timescale for an SMBH binary merger and may also cause the ejection of the lightest SMBH from the system (Saslaw et al. 1974; Volonteri et al. 2003; Hoffman & Loeb 2007; Bonetti et al. 2016, 2018a).”
Massive Black Hole Binary Mergers in Dynamical Galactic Environments (2016, background): “If the interaction between MBH triples (or even higherorder multiples) is indeed most similar to scattering, then the simplest prescription of removing the lowest-mass BH, with or without some additional hardening of the more massive pair, may still be appropriate (e.g. Hoffman & Loeb 2007).”
The Eccentric Kozai-Lidov Effect and Its Applications (2016, background): “…black holes, one expects that major galaxy mergers should inevitably result in the formation of supermassive black hole binaries or multiples (e.g., Valtonen 1996; Di Matteo et al. 2005; Hoffman and Loeb 2007; Callegari et al. 2009; Dotti et al. 2012; Khan et al. 2012; Kulkarni and Loeb 2012).”
Rapid Eccentricity Oscillations and the Mergers of Compact Objects in Hierarchical Triples (2013, methodology): “In this paper we revisit earlier calculations of the merger times of compact objects by Blaes et al. (2002) and Hoffman & Loeb (2007).”
RESONANT POST-NEWTONIAN ECCENTRICITY EXCITATION IN HIERARCHICAL THREE-BODY SYSTEMS (2012, background): “…paradigm, and the strong evidence that a high abundance of the local galaxies host supermassive BHs (SMBHs), one expects that major galaxy mergers should inevitably result in the formation of SMBH binaries or multiples (Valtonen 1996; Hoffman & Loeb 2007; Kulkarni & Loeb 2012; Dotti et al. 2012).”
Gravitational waves from resolvable massive black hole binary systems and observations with Pulsar Timing Arrays (2008, background): “This is because triple interactions are likely to eject the lighter MBH from the host, leaving behind a massive binary in the vast majority of the cases (Volonteri Haardt & Madau 2003, Hoffman & Loeb 2007).”
Science with the space-based interferometer eLISA. III: probing the expansion of the universe using gravitational wave standard sirens (2016, background): “Kozai resonances may then trigger the merger of the two heaviest BHs (and ejection of the lightest) in ∼ 108 yr [63], at least for BH masses & 106 − 107M .”