Clumpy outflows from super-Eddington accreting black holes. I. Radiation hydrodynamics simulations and observational implications

Abstract Recent advances in X-ray spectroscopic observation have enabled researchers to reveal distinct clumpy structures in the super-Eddington outflows from the supermassive black hole in PDS 456 (XRISM Collaboration 2025, Nature, 641, 1132), initiating detailed investigation of fine-scale structures in accretion-driven outflows. In this study, we conduct high-resolution, two-dimensional radiation hydrodynamics simulations with time-varying and anisotropic initial and boundary conditions to reproduce outflows launched from super-Eddington accretion flows and analyze their statistical properties. The resulting clumpy outflows extend across a wide range of radial distances and polar angles, exhibiting typical properties such as a size of ${\sim }10~r_{\rm g}$ (where $r_{\rm g}$ is the gravitational radius), a velocity of $\sim$0.05–$0.2~c$ (where c is the speed of light), and about five clumps along the line of sight. Although the velocities are slightly smaller, these characteristics reasonably resemble those obtained from the XRISM observation. The gas density of the clumps is of the order of $10^{-12}$–$10^{-13}~{\rm g~cm^{-3}}$, and their optical depth for electron scattering is approximately 1–10. The clumpy winds accelerated by radiation force are considered to originate from the region within ${\lesssim }300~r_{\rm g}$.