Misaligned Spinning Binary Black Hole Mergers in Hot Magnetized Plasma

TL;DR

This study uses relativistic magneto-hydrodynamical simulations to explore how the spin orientation of merging black holes in a magnetized plasma affects accretion dynamics and electromagnetic signals, revealing potential observational signatures.

Contribution

It introduces detailed simulations of spinning black hole mergers in magnetized gas, highlighting the impact of spin orientation on accretion and electromagnetic emissions.

Findings

Quasi-periodic accretion rate modulations correlate with gravitational wave signals.

Disk-like overdensities form around black holes, aligned with their spins.

Electromagnetic signatures may accompany gravitational wave detections in such environments.

Abstract

We present general relativistic magneto-hydrodynamical simulations of equal-mass spinning black hole binary mergers embedded in a magnetized gas cloud. We focus on the effect of the spin orientation relative to the orbital angular momentum on the flow dynamics, mass accretion rate and Poynting luminosity. We find that, across the inspiral, the gas accreting onto the individual black holes concentrates into disk-like overdensities, whose angular momenta are oriented towards the spin axes and which persist until merger. We identify quasi-periodic modulations occurring in the mass accretion rate at the level of 1-20%, evolving in parallel with the gravitational wave chirp. The similarity between the accretion rate time-series and the gravitational strain is a consequence of the interplay between strong, dynamical gravitational fields and magnetic fields in the vicinity of the inspiralling black holes. This result suggests that quasi-periodicity in the pre-merger accretion rate of massive binaries is not exclusive of environments in which the black holes are embedded in a circumbinary accretion disk, and could provide an additional useful signature of electromagnetic emission concurrent to low-frequency gravitational wave detection.