Accretion, Jets, and Recoil in Merging Supermassive Binary Black Holes

Abstract

We report the first 3D general relativistic magnetohydrodynamic (GRMHD) simulation that captures the full, self-consistent evolution from the late inspiral through merger and subsequent recoil of a supermassive binary black hole (SMBBH) with misaligned spins embedded in an equilibrated circumbinary disk (CBD). Our full numerical simulation follows the final 40 orbits of the inspiral and merger of the binary, following an initial phase of 165 orbits of CBD evolution toward equilibrium. We find that the jets, launched from the minidisks surrounding each black hole, are tilted toward the black hole spin direction close to the individual black holes, but align with the binary's total angular momentum at larger distances. Following the merger, the remnant black hole receives a recoil kick exceeding 1000 km/s. Remarkably, it retains its gravitationally bound CBD as if it were ejected from a galactic nucleus. Furthermore, the jet launched by the recoiling remnant black hole preserves the large-scale orientation established during the late inspiral. We demonstrate that the majority of the luminosity emerges from a region in close proximity to the black hole, suggesting that the accretion disk surrounding the recoiling remnant would remain the most luminous feature postmerger, persisting for long enough to be observable by modern telescopes (hours in the case of LISA sources). These findings introduce a direct, first-principles model for the recoil of supermassive black holes (SMBH) in active galactic nuclei (AGNs), offering a comprehensive theoretical basis to support and elucidate both ongoing and future observational efforts.

Figures (3)

• Figure 1: Equatorial and polar slices of the rest-mass density are shown at four representative stages of the simulation, with slice positions following the black holes' motion. Fig. \ref{['fig:1a']} displays the initial configuration of the circumbinary disk. Fig. \ref{['fig:1b']} and Fig. \ref{['fig:1d']} show the pre-merger system with magnetic field lines overlaid; in both snapshots the black holes lie closely to the x-axis. Fig. \ref{['fig:1d']} captures the entire disk as it remains gravitationally bound and moves along with the recoiling remnant, whose trajectory along the negative z-axis is highlighted in the insets.
• Figure 2: Equatorial and polar slices of the CBD carried out by the remnant black hole at three different times during the postmerger. Zoomed insets highlight the disk's displacement along the z-axis (with a black dashed line marking the origin, $z=0$), consistent with the recoil velocity ($v_{\text{kick}} \simeq 1032\,\text{km/s} \simeq 0.0034 \ c$) of the remnant black hole. Velocity magnitude streamlines, defined as $|v|= \sqrt{v_x^2+v_z^2}$, are overplotted in the top panels.
• Figure 3: (Top) Poynting (EM energy) flux computed on a $45^\circ$ aperture cone above and below the orbital plane at radius $r=100 \ M$. (Center) Bolometric EM luminosity obtained by integrating the cooling rate over spheres of radii $r=15 \ M$ and $r=100 \ M$. (Bottom) Total mass accretion rate onto the black hole horizons $\dot{M}=\dot{M}_{BH_1}+ \dot{M}_{BH_2}$. A black vertical dashed line marks the merger time.