General Relativistic Magnetohydrodynamic Simulations of Circumbinary Disk Accretion onto Merging Unequal Mass Black Hole Binaries

Accreting supermassive binary black holes (SMBBHs), which are the expected outcome of galaxy mergers, are potential powerful multimessenger sources of gravitational waves (GWs) and electromagnetic (EM) radiation. The latter may be periodically modulated by an asymmetric density distribution in the circumbinary disk (CBD), typically referred to as the “lump”. Possible enhancement of this modulation is predicted to occur when considering unequal mass binaries. In that scenario the less massive black hole (often called the "secondary") is expected to consume a majority of the inflowing gas as it gets closer to the inner edge of the CBD possibly dominating the overall EM luminosity.

We perform the first set of full 3D general relativistic magnetohydrodynamic (GRMHD) simulations of merging unequal mass (q=1:2) black hole binaries, both spinning and non spinning, embedded in a CBD, adopting the IllinoisGRMHD code. We use relaxed initial data for the CBD, retrieved from a previous long-term simulation, performed with the SphericalNR code, which employs curvilinear coordinates and a post-Newtonian (PN) metric with a cutout excising the central region containing the binary. We study the dependence of multiple diagnostics, including the mass accretion rate, the Poynting flux and the mass enclosed at different radii, on the spins of the black holes and their mass ratio. Additionally, we analyze the dynamics and structure of the minidisks surrounding each black hole and the evolution of the jets ejected by them.