GRMHD simulations of accretion flows onto unequal-mass, precessing massive binary black hole mergers

In this work, we use general relativistic magnetohydrodynamics simulations to explore the effect of spin orientation on the dynamics of gas in the vicinity of merging black holes. We present a suite of eight simulations of unequal-mass, spinning black hole binaries embedded in magnetized clouds of matter. Each binary evolution covers approximately 15 orbits before the coalescence. The geometry of the accretion flows in the vicinity of the black holes is significantly altered by the orientation of the individual spins with respect to the orbital angular momentum, with the primary black hole dominating the mass accretion rate Ṁ. We observe quasiperiodic modulations of Ṁ in most of the configurations, whose amplitude is dependent on the orientation of the black hole spins. We find the presence of a relation between the average amplitude of Ṁ and the spin precession parameter χp showing that spin misalignment systematically leads to stronger modulation, whereas configurations with spins aligned to the orbital angular momentum damp out the quasiperiodicity. This finding suggests a possible signature imprinted in the accretion luminosity of precessing binaries approaching merger and has possible consequences on future multimessenger observations of massive binary black hole systems.