Binary Black-Hole Mergers in Magnetized Disks: Simulations in Full General Relativity

TL;DR

This paper presents the first fully general relativistic magnetohydrodynamic simulations of an equal-mass black hole binary in a magnetized disk, revealing complex accretion and outflow behaviors before and after merger, with implications for multimessenger astronomy.

Contribution

It provides the first comprehensive GRMHD simulation of a black hole binary in a magnetized disk, including pre- and post-merger phases and cooling effects.

Findings

Disk depletion due to tidal and viscous torques before decoupling

Induction of two-stream accretion and polar outflows

Electromagnetic luminosity enhancement after merger

Abstract

We present results from the first fully general relativistic, magnetohydrodynamic (GRMHD) simulations of an equal-mass black hole binary (BHBH) in a magnetized, circumbinary accretion disk. We simulate both the pre and post-decoupling phases of a BHBH-disk system and both "cooling" and "no-cooling" gas flows. Prior to decoupling, the competition between the binary tidal torques and the effective viscous torques due to MHD turbulence depletes the disk interior to the binary orbit. However, it also induces a two-stream accretion flow and mildly relativistic polar outflows from the BHs. Following decoupling, but before gas fills the low-density "hollow" surrounding the remnant, the accretion rate is reduced, while there is a prompt electromagnetic (EM) luminosity enhancement following merger due to shock heating and accretion onto the spinning BH remnant. This investigation, though preliminary, previews more detailed GRMHD simulations we plan to perform in anticipation of future, simultaneous detections of gravitational and EM radiation from a merging BHBH-disk system.