Accretion onto supermassive black hole binaries

TL;DR

This paper reviews current understanding and recent advances in modeling accretion processes onto supermassive black hole binaries, emphasizing numerical simulations and their implications for observable signatures.

Contribution

It provides a comprehensive overview of modeling techniques, recent developments in GRMHD simulations, and discusses open problems in the study of accreting supermassive black hole binaries.

Findings

Insights into the dynamics of circumbinary and mini-disks

Analysis of electromagnetic signatures from accreting binaries

Evaluation of numerical simulation approaches

Abstract

In this chapter, we give an overview of our current understanding of the physics of accreting massive black hole binaries (MBHBs), with a special focus on the latest developments in numerical simulations and General-Relativistic Magnetohydrodynamics (GRMHD) simulations in particular. We give a self-contained global picture of how to model accretion onto MBHBs, analyzing different aspects of the system such as the dynamics of the circumbinary disk, mini-disks, outflows, the role of magnetic fields, and electromagnetic signatures. We discuss important questions and open problems related to these systems, what are the advantages and disadvantages of the different numerical approaches, and what robust knowledge we have built from simulations.