Characteristic Signatures in the Thermal Emission from Accreting Binary Black Holes

TL;DR

This study models the thermal emission from a supermassive black hole binary system using high-precision hydrodynamical simulations, revealing characteristic spectral signatures due to accretion dynamics.

Contribution

It provides the first detailed simulation of the thermal spectrum including viscous, shock heating, and cooling effects in a binary black hole system.

Findings

Gas streams feed mini-disks around black holes

Shock heating prevents high-energy deficits in the spectrum

Spectral brightening begins in soft X-rays

Abstract

We present the results of a calculation of the thermal spectrum from a 2D, moving mesh, high-accuracy, viscous hydrodynamical simulation of an accreting supermassive black hole binary. We include viscous heating, shock heating, and radiative cooling, evolving for longer than a viscous time so that we reach a quasi-steady accretion state. In agreement with previous work, we find that gas is efficiently stripped from the inner edge of the circumbinary disk and enters the cavity along accretion streams, which feed persistent "mini-disks" surrounding each black hole. We also find that emission from the shock-heated mini-disks and accretion streams prevents any deficit in high-energy emission that may be expected inside the circumbinary cavity, and instead leads to a characteristic brightening of the spectrum beginning in soft X-rays.