| Abstract: When galaxies merge, their central massive black holes do not necessarily merge with them. Whether and when they coalesce depends on their interactions with gas and stars, and sometimes with a third black hole, across scales that galaxy simulations cannot resolve. In this talk, I will present RAMCOAL, a subgrid model integrated into RAMSES that follows massive black hole pairs to coalescence within their evolving host galaxies. RAMCOAL couples orbital evolution to accretion, feedback and spin evolution, bridging the gap between resolved galaxy dynamics and the scales where gravitational waves drive the final inspiral. I will show tests of the model’s robustness to numerical resolution and introduce RAMCOAL-3body, its extension to interacting black hole triplets. I will then present preliminary simulations of BlackTHUNDER, a galaxy at redshift z ≈ 5 where JWST finds evidence for three accreting massive black holes, and explore their possible merger history. Finally, I will discuss ongoing cosmological applications with COSCOAL. This work aims to connect observed black hole pairs and triplets to their eventual mergers and predict their gravitational wave and electromagnetic signatures for multimessenger studies with LISA and pulsar timing arrays. Link to the Event Video |