General Relativistic Simulations of Magnetized Plasmas around Merging Supermassive Black Holes

TL;DR

This paper presents the first general relativistic simulations of magnetized plasma around merging supermassive black holes, revealing magnetic field amplification and potential electromagnetic signals associated with gravitational wave sources.

Contribution

It introduces the first simulations of magnetized plasma in merging supermassive black hole binaries using GRMHD, highlighting magnetic amplification effects and electromagnetic emission predictions.

Findings

Magnetic fields can be amplified by about 100 times during mergers.

Electromagnetic signals can be over 10,000 times stronger than previous force-free estimates.

Magnetic field dynamics significantly influence plasma behavior around merging black holes.

Abstract

Coalescing supermassive black hole binaries are produced by the mergers of galaxies and are the most powerful sources of gravitational waves accessible to space-based gravitational observatories. Some such mergers may occur in the presence of matter and magnetic fields and hence generate an electromagnetic counterpart. In this Letter, we present the first general relativistic simulations of magnetized plasma around merging supermassive black holes using the general relativistic magnetohydrodynamic code Whisky. By considering different magnetic field strengths, going from non-magnetically dominated to magnetically dominated regimes, we explore how magnetic fields affect the dynamics of the plasma and the possible emission of electromagnetic signals. In particular we observe a total amplification of the magnetic field of ~2 orders of magnitude which is driven by the accretion onto the binary and that leads to much stronger electromagnetic signals, more than a factor of 10^4 larger than comparable calculations done in the force-free regime where such amplifications are not possible.