General relativistic magnetohydrodynamical simulations of accretion onto spinning black-hole binaries.

Massive black-hole binary (MBHB) mergers are mighty gravitational wave (GW) events, which will be detected by future space-based laser interferometers such as LISA. MBHBs are a natural outcome of the hierarchical process of galaxy mergers, and their coalescence may occur in a magnetized, gas-rich environment, yielding powerful electromagnetic (EM) emissions. To explore the features of the plasma surrounding these binaries, we produce a suite of general relativistic magnetohydrodynamical (GRMHD) simulations of the late-inspiral and merger of MBHBs. Our work models for the first time the GRMHD evolution of binaries of spinning black holes, with spins either aligned or misaligned to the orbital angular momentum. Our goal is to capture the effects of spins on the mass accretion rate, the gas dynamics, and the EM energy emitted during the binary late-inspiral and merger. We identify quasiperiodic modulations in the premerger accretion rate that evolve in parallel with the GW signal. This result could provide a valuable signature of EM emission concurrent to low-frequency GW detection, offering a novel outlook for future multimessenger astronomy.