Bridging Bondi and Event Horizon Scales: 3D GRMHD Simulations Reveal X-Shaped Radio Galaxy Morphology

Abstract

X-shaped radio galaxies (XRGs) produce misaligned X-shaped jet pairs and make up $\lesssim 10\%$ of radio galaxies. XRGs are thought to emerge in galaxies featuring a binary supermassive black hole ($\mathrm{SMBH}$), $\mathrm{SMBH}$ merger, or large-scale ambient medium asymmetry. We demonstrate that XRG morphology can naturally form without such special, preexisting conditions. Our 3D general-relativistic magnetohydrodynamic (GRMHD) simulation for the first time follows magnetized rotating gas from outside the $\mathrm{SMBH}$ sphere of influence of radius $R_{\mathrm{B}}$ to the $\mathrm{SMBH}$ of gravitational radius $R_{\mathrm{g}}$, at the largest scale separation $R_{\mathrm{B}}/R_{\mathrm{g}}=10^3$ to date. Initially, our axisymmetric system of constant-density hot gas contains weak vertical magnetic field and rotates in an equatorial plane of a rapidly spinning $\mathrm{SMBH}$. We seed the gas with small-scale $2\%$-level pressure perturbations. Infalling gas forms an accretion disk, and the $\mathrm{SMBH}$ launches relativistically-magnetized collimated jets reaching well outside $R_{\mathrm{B}}$. Under the pressure of the infalling gas, the jets intermittently turn on and off, erratically wobble, and inflate pairs of cavities in different directions, resembling an X-shaped jet morphology. Synthetic X-ray images reveal multiple pairs of jet-powered shocks and cavities. Large-scale magnetic flux accumulates on the $\mathrm{SMBH}$, becomes dynamically important, and leads to a magnetically arrested disk state. The $\mathrm{SMBH}$ accretes at $2\%$ of the Bondi rate ($\dot{M}\simeq 2.4\times 10^{-3}{M}_{\odot }{\mathrm{yr}}^{-1}$ for M87*), and launches twin jets at $\eta =150\%$ efficiency. These jets are powerful enough ($P_{\mathrm{jets}}\simeq 2\times 10^{44}{\mathrm{erg}\mathrm{s}}^{-1}$) to escape along the spin axis and end the short-lived jets state whose transient nature can account for the rarity of XRGs

10 pages, 4 figures

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