Appears in collection : Balzan Conference on Open Issues in Gravitation

We investigate the astrophysical environments of supermassive black hole binaries approaching merger using advanced General Relativistic Magnetohydrodynamics (GRMHD). Our simulations focus on the interplay between circumbinary disks and the magnetized accretion flows onto individual spinning black holes. By accurately modeling these relativistic environments, we provide essential data for predicting the electromagnetic counterparts to gravitational wave events. These findings are instrumental for informing observational strategies for upcoming missions, including LISA and other high-cadence astronomical facilities.