Abstract

Supermassive black holes (SMBHs), which reside at the centres of massive galaxies and co-evolve with them, are expected to form binaries following galaxy mergers, a natural outcome of hierarchical galaxy formation. The orbital evolution of these SMBH binaries is driven by a range of physical processes acting across vastly different length scales: from kiloparsec separations, where the dynamics of merging galaxies dominate, down to sub-parsec scales where interactions with gas and, eventually, gravitational wave emission become the primary drivers of orbital decay. In this talk, I will present an overview of the key hardening mechanisms that govern SMBH binary evolution, highlight recent progress in the field, and share insights from my own research on the dynamics of these systems.