Abstract

Contributed Talk - Splinter StarClusters   (MW-2050)

The effect of triaxial stellar environments on the dynamics of triple supermassive black holes in a cosmological context

Navonil Saha, Margarita Sobolenko, Peter Berczik, Andreas Just, Fazeel Mahmood Khan
Astronomisches Rechen-Institut, Universität Heidelberg

The hierarchical nature of galaxy formation in the ΛCDM cosmological framework naturally leads to repeated galaxy mergers and, consequently, to the presence of multiple supermassive black holes (SMBHs) in galactic nuclei. The timescale over which galaxies merge plays a crucial role in shaping the dynamical evolution and eventual coalescence of their central SMBHs. SMBH mergers are among the primary low frequency gravitational wave sources targeted by future observatories such as LISA, and their evolution is governed by interactions with the dense stellar environments of galactic nuclei, where nuclear star clusters and surrounding stellar populations efficiently extract orbital energy and angular momentum from SMBH systems through the process of dynamical friction and then later three-body interaction. While the evolution of SMBH binaries has been studied extensively, the long term dynamics of triple SMBH systems, particularly in realistic, non spherical stellar environments, remain poorly understood. In this work, we investigate the role of triaxiality in shaping the dynamical evolution of triple SMBH systems extracted from the ROMULUS25 cosmological simulation and embedded in dense triaxial stellar backgrounds using high resolution direct N-body simulations. We explore a range of orbital configurations and host galaxy shapes, following the orbital evolution from the galactic inspiral phase to the formation of hard SMBH binaries at sub parsec separations, and use the measured hardening rates to estimate their coalescence timescales. In all cases, the two most massive black holes form an efficiently hardening binary that is expected to merge within a Hubble time, while the third SMBH either settles into a long-lived hierarchical triple configuration or remains on a wider galactic orbit. Finally, we analyse the triaxiality of the stellar remnant and find that the initial triaxial shape of the host galaxy does not have a strong influence on the final dynamical outcome of the triple systems.