Binary AGN simulations with radiation pressure reveal a new duty cycle, and a reduction of gravitational torque, through 'minitori' structures

TL;DR

This study uses radiation hydrodynamics simulations to explore how radiation pressure affects binary AGN evolution, revealing a new duty cycle and reduced gravitational torques due to 'minitori' structures.

Contribution

First radiation hydrodynamics simulations of binary AGNs at parsec scales showing radiation pressure destroys 'minitori', alters torque, and introduces a new activity duty cycle.

Findings

Radiation pressure destroys 'minitori', reducing gravitational torques.

A new 'minitorus' duty cycle of ~10^6 years is proposed.

Approximately half of observed binary SMBHs may be active at any time.

Abstract

We produce the first set of radiation hydrodynamics simulations of binary 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 $<10^9$ yr. However, radiation pressure quickly destroys the 'minitori' around each 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 (~$10^6$ yr when scaling our models to a total binary mass of $2\times10^7\,M_\odot$). 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.