Binary AGNs simulations with radiation pressure reveal a new duty cycle, and a reduction of gravitational torque, through ‘minitori’ structures

Abstract

ABSTRACT We produce the first set of radiation hydrodynamics simulations of binary active galactic nuclei (AGNs) at parsec-scale separation in scale-model simulations. We use SPH for hydrodynamics, and raytracing to calculate optical depths and radiation pressure from the two AGNs. We confirm that, without radiation pressure, the sign of gravitational torque is sensitive to the binary parameters, although in one of our two orbital configurations the binary should coalesce in a time-scale of <109 yr. However, radiation pressure quickly destroys the ‘minitori’ around each supermassive black hole (SMBH), drastically reducing gravitational torques and accretion, and greatly increasing the coalescence time-scale. Our simulations suggest a new ‘minitorus’ duty cycle with a time-scale of ∼10 binary periods (∼106 yr when scaling our models to a total binary mass of 2 × 107 M⊙). The growth and blow-out phases of the ‘minitori’ are of similar time-scales, and thus we expect about half of observed binary SMBHs to be active, in at least one component. The ‘minitorus’ structure provides asymmetries that could be observed by infrared interferometry.