Set them free: extending RAMCOAL to model massive black hole triplets in hydrodynamical simulations of galaxies
Abstract
Massive black hole binaries (MBHBs) and the higher-order multiples produced by repeated galaxy mergers evolve through regimes that cosmological simulations cannot resolve. These regimes determine merger delays, spins, recoils, and host galaxies at coalescence. We extend the RAMCOAL subgrid model to follow massive black hole triplets within hydrodynamical galaxy simulations. In the original three-stage binary model, black holes evolve as sink particles, undergo dynamical friction, and form bound binaries that harden through stellar scattering, gas torques, circumbinary-disc coupling, and gravitational-wave emission. When a hierarchical triplet becomes chaotic, RAMCOAL samples a library of outcomes from direct N body experiments and follows the resulting mergers, exchanges, and ejections alongside the accretion and spin evolution of each black hole. Isolated-galaxy tests with different triplet geometries show that orbital configuration alone can change which pair merges and its coalescence time. For the first time, we follow an MBH triplet to coalescence within a hydrodynamical simulation of gas-rich galaxies, coupling triplet-driven mergers to host-galaxy evolution. Subgrid integration costs less than 1 ms of single-core time per MBH system and time step, independently of particle resolution. The resulting coalescence properties reflect the environment encountered during subgrid evolution. RAMCOAL thus provides a step towards merger catalogues linking gravitational-wave signatures to the galaxies in which the black holes evolve.
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BibTeX
@misc{li2026them,
title = {{Set them free: extending RAMCOAL to model massive black hole triplets in hydrodynamical simulations of galaxies}},
author = {Kunyang Li and Ricarda S. Beckmann and Yohan Dubois and Marta Volonteri},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2607.04121},
eprint = {2607.04121},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.04121},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Set them free: extending RAMCOAL to model massive black hole triplets in hydrodynamical simulations of galaxies
AU - Kunyang Li
AU - Ricarda S. Beckmann
AU - Yohan Dubois
AU - Marta Volonteri
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2607.04121
UR - https://arxiv.org/abs/2607.04121
AB - Massive black hole binaries (MBHBs) and the higher-order multiples produced by repeated galaxy mergers evolve through regimes that cosmological simulations cannot resolve. These regimes determine merger delays, spins, recoils, and host galaxies at coalescence. We extend the RAMCOAL subgrid model to follow massive black hole triplets within hydrodynamical galaxy simulations. In the original three-stage binary model, black holes evolve as sink particles, undergo dynamical friction, and form bound binaries that harden through stellar scattering, gas torques, circumbinary-disc coupling, and gravitational-wave emission. When a hierarchical triplet becomes chaotic, RAMCOAL samples a library of outcomes from direct N body experiments and follows the resulting mergers, exchanges, and ejections alongside the accretion and spin evolution of each black hole. Isolated-galaxy tests with different triplet geometries show that orbital configuration alone can change which pair merges and its coalescence time. For the first time, we follow an MBH triplet to coalescence within a hydrodynamical simulation of gas-rich galaxies, coupling triplet-driven mergers to host-galaxy evolution. Subgrid integration costs less than 1 ms of single-core time per MBH system and time step, independently of particle resolution. The resulting coalescence properties reflect the environment encountered during subgrid evolution. RAMCOAL thus provides a step towards merger catalogues linking gravitational-wave signatures to the galaxies in which the black holes evolve.
ER -