The AGN Channel in 3D: Scattering Belts and the Importance of Eccentricity in the Black Hole Population
Abstract
Active galactic nuclei (AGN) are a promising origin for observed gravitational wave mergers. Current population synthesis models are limited to 1D N-body or Monte Carlo methods which rely on statistical approaches to resolving dynamical scatterings. We present three-dimensional hybrid N-body simulations of a population of black holes (BHs) surrounding an AGN using a new code in development, AGNBI, where close interactions are directly simulated for both single and binary objects. Our results show binary formations occur throughout the AGN disk, particularly where the migration time is long. While BHs efficiently migrate and pair up in migration traps, they are frequently disrupted by ionisation or exchanges from binary-single and binary-binary interactions. We report a broadened radial distribution of formations and mergers about the trap radius when accounting for binary-single and binary-binary interactions, which we describe as a "scattering belt''. We assess the influence of the pre-existing BH population. When we model a non-zero eccentricity distribution in the BH population, the binary formations and mergers are suppressed by an order of magnitude compared to a non-eccentric population as fewer BHs embed in the AGN disk. We report an approximate merger rate of ℛGW≈2−−12 Gpc−3 yr−1 with maximum BH masses of 102−−103 M⊙ through hierarchical mergers, where lower initial velocity dispersions produce larger BHs. The mass and mass ratio distributions are comparatively flat, suggesting AGN may be more relevant for high-mass or unequal-mass gravitational wave sources.
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BibTeX
@misc{rowan2026channel,
title = {{The AGN Channel in 3D: Scattering Belts and the Importance of Eccentricity in the Black Hole Population}},
author = {Connar Rowan and Martin E. Pessah},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.22074},
eprint = {2609.22074},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.22074},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The AGN Channel in 3D: Scattering Belts and the Importance of Eccentricity in the Black Hole Population
AU - Connar Rowan
AU - Martin E. Pessah
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.22074
UR - https://arxiv.org/abs/2609.22074
AB - Active galactic nuclei (AGN) are a promising origin for observed gravitational wave mergers. Current population synthesis models are limited to 1D N-body or Monte Carlo methods which rely on statistical approaches to resolving dynamical scatterings. We present three-dimensional hybrid N-body simulations of a population of black holes (BHs) surrounding an AGN using a new code in development, AGNBI, where close interactions are directly simulated for both single and binary objects. Our results show binary formations occur throughout the AGN disk, particularly where the migration time is long. While BHs efficiently migrate and pair up in migration traps, they are frequently disrupted by ionisation or exchanges from binary-single and binary-binary interactions. We report a broadened radial distribution of formations and mergers about the trap radius when accounting for binary-single and binary-binary interactions, which we describe as a "scattering belt''. We assess the influence of the pre-existing BH population. When we model a non-zero eccentricity distribution in the BH population, the binary formations and mergers are suppressed by an order of magnitude compared to a non-eccentric population as fewer BHs embed in the AGN disk. We report an approximate merger rate of ℛ_GW≈2−−12 Gpc^−3 yr^−1 with maximum BH masses of 10^2−−10^3 M_⊙ through hierarchical mergers, where lower initial velocity dispersions produce larger BHs. The mass and mass ratio distributions are comparatively flat, suggesting AGN may be more relevant for high-mass or unequal-mass gravitational wave sources.
ER -