Multimessenger Signatures of Tilted, Self-Gravitating, Black Hole Disks

Abstract

We perform fully relativistic GRMHD simulations of magnetized, self-gravitating black hole-disk (BHD) systems in which the black hole spin is misaligned with the disk angular momentum. Massive disks (disk to BH mass ratios of $16-28\%$) around rapidly rotating black holes ($χ\lesssim 0.97$) develop a nonaxisymmetric instability for tilt angles from $0^\circ$ to $180^\circ$. Magnetic stresses damp, but do not completely suppress, the nonaxisymmetric instability, and corresponding gravitational wave (GW) emission, in aligned systems, while they enhance it in antialigned BHDs: MRI-driven turbulence enhances angular momentum transport and accelerates nonlinear instability evolution in misaligned configurations. All models launch magnetically driven jets consistent with the Blandford-Znajek (BZ) mechanism, with collimation depending on spin orientation. The GWs reflect strong nonaxisymmetric structure from a persistent $m=1$ mode. The coupling between fast MRI and the slower nonaxisymmetric instability growth governs the outcome, with tilt controlling how MRI modifies the global mode. These simulations provide the first self-consistent GRMHD treatment of tilted, self-gravitating BHD systems and support their role as multimessenger sources.

Figures (11)

• Figure 1: Volume rendering of the initial BHD system threaded by a purely poloidal magnetic field. The BH is depicted as a black spheroid. The yellow arrow shows the initial spin direction for case A2 $(45^\circ)$, while the fainter arrows indicate the spin orientations for other cases (see Table I in Tsokaros:2022hjk).
• Figure 2: Volume rendering of the rest-mass density $\rho_0$ for the final outcome of BHDs (see Table I in Tsokaros:2022hjk), normalized to its initial maximum value (log scale). In all cases, a magnetically-driven, collimated outflow (jet) emerges along the BH polar regions. Arrows denote fluid velocities while white lines trace the magnetic field, illustrating its collimation into a jet-like structure. Here the period $P_c/M=\{370,404,357,422\}$.
• Figure 3: Volume rendering of the rest-mass density $\rho_0$ in the disk (color bar same as in Fig. \ref{['fig:final_outcome']}), and magnetization $B^2/(8\pi\rho_0)$ (log scale) in the funnel region near the end of simulation A2. White field lines mark regions with $B^2/(8\pi\rho_0)\gtrsim10^{-2}$. The inset shows horizon-threading field lines, magnetically dominated polar regions, and inner-disk alignment with the BH spin.
• Figure 4: Evolution of the amplitudes of the non axisymmetric $m=1$ and $m=2$ density modes, normalized by the $m=0$ mode. Solid lines denote the magnetized cases, while dashed lines indicate the unmagnetized cases reported in Tsokaros:2022hjk.
• Figure 5: Time evolution of the BH angular momentum components $J_i^{\rm BH}$ (colored) and magnitude $|J^{\rm BH}|$ (grey) for tilted cases A2 ($45^\circ$; top) and A3 ($90^\circ$; bottom).