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arXiv · 2510.20466

The effect of triaxiality on the dynamics of triple supermassive black holes in a cosmological context

Navonil Saha·Peter Berczik·Andreas Just·Margarita Sobolenko
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Abstract

The hierarchical nature of galaxy formation in the $\Lambda$CDM framework often leads to multiple supermassive black holes (SMBHs) in the galactic nuclei. The timescale over which galaxies merge, plays a crucial role in shaping the dynamical evolution and the merger dynamics of their central SMBHs. While binary SMBH evolution is well studied, the long-term dynamics of triple SMBH systems, particularly in non-spherical potentials, remain less understood. We investigate the role of triaxiality in the evolution and dynamics of triple SMBHs with initial conditions drawn from the ROMULUS25 cosmological simulation, using high-resolution gravitodynamical N-body simulations. We explore different orbital configurations and host shapes, tracking the evolution from galactic inspiral to hard binary formation at sub-parsec scales. In all cases, the two most massive SMBHs form a rapidly hardening binary that coalesces within a fraction of a Hubble time, while the third forms a stable hierarchical triple system with the heavier binary, or remains on a wide orbit.

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Navonil Saha, Peter Berczik, Andreas Just, Margarita Sobolenko. 2025-10-23. The effect of triaxiality on the dynamics of triple supermassive black holes in a cosmological context. https://arxiv.org/abs/2510.20466

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