Recoil geometry determines electromagnetic counterparts from supermassive black hole merger remnants

Abstract

Merging binary black holes embedded in gaseous environments, such as supermassive black hole binaries following gas-rich galaxy mergers, are promising sources of multi-messenger transients in the upcoming age of space-based gravitational wave detections. In case a gravitational radiation recoil is imparted to the merger remnant, subsequent interactions between the recoiled black hole and its circumbinary disk may lead to unique post-merger electromagnetic counterparts. We present the first general relativistic magnetohydrodynamic simulations of a recoiling black hole interacting with a magnetically arrested circumbinary disk the evolution of which has been consistently tracked through the inspiral phase. We show that the post-merger accretion dynamics, depending on the recoil geometry, exhibits qualitatively disparate jet and disk behavior. For recoils perpendicular to the disk, the inner disk remains gravitationally bound and sustains relativistic jets, while in-plane recoils lead to copious shock heating and potential jet quenching for black holes directly colliding with the disk. Oblique recoils, on the other hand, produce intermittent outbursts from jet-disk interactions owing to the tilt introduced in the accretion disk. Multi-wavelength monitoring of these electromagnetic counterparts, in conjunction with the coincident gravitational wave detection, will be able to aid in characterizing the physical conditions of the merger environment.

Figures (8)

• Figure 1: Three-dimensional view of the rest-mass density (white-blue) and the relativistic magnetization parameter $\sigma$ (red-yellow) from the simulations with a vertical recoil at $v_rt = 1934 r_g$ (left), an oblique recoil at $v_r t = 1354 r_g$ (center), and a horizontal recoil at $v_r t = 166 r_g$ (right), all for the recoil speed $v_r = 0.05c$. Location and recoil direction of the BH are shown with a dotted arrow. Key features are annotated with plain texts.
• Figure 2: A zoom-in view of an jet outburst episode in the obliquely recoiled model (v005$\nearrow$). Each panels have the same viewing angle as in the center panel in Fig. \ref{['fig:volume-rendering']}, and correspond to simulation times $t =$ (i) $2.8\times 10^{4} r_g c^{-1}$, (ii) $3.9\times 10^{4} r_g c^{-1}$, (iii) $4.6\times 10^{4} r_g c^{-1}$, (iv) $5.0\times 10^{4} r_g c^{-1}$.
• Figure 3: Magnetization parameter $\sigma$ (red) and the internal energy density (bright blue) in the v005$\rightarrow$ model at $v_rt = 332 r_g$ (left) and $v_rt = 663 r_g$ (right), showing the jet and the distribution of the shock-heated gas. The recoiled BH (not visible here) is moving to the right side of the figure.
• Figure 4: (i) Rest-mass density distribution on the equatorial plane in the v005$\rightarrow$ model at $v_rt=207r_g$. (ii) The recoiling BH is in the MAD state and surrounded by a strongly magnetized accretion flow ($\sigma \gtrsim 1$). (iii) A fraction of the CBD cavity survives as a magnetized low-density blob, then being advected and sheared by ambient gas flow. The in-plane magnetic field lines (white solid curves) reveal multiple X-points, the site of active magnetic reconnection.
• Figure 5: Total gas internal energy $U(t)$ contained within a spherical volume $r < 1200 r_g$ centered to the original circumbinary disk, normalized with its initial value. Horizontal scales are time (left) and the recoil distance (right).