Three-dimensional structure of clumpy outflow from supercritical accretion flow onto black holes

TL;DR

This study uses 3D radiation-hydrodynamic simulations to reveal the detailed structure and dynamics of clumpy outflows from supercritical black hole accretion disks, showing their shapes, rotation, and potential observational signatures.

Contribution

It is the first to perform full 3D simulations of clumpy outflows from supercritical accretion flows, revealing their shapes, rotation, and variability.

Findings

Clumpy outflows form above the photosphere at a few hundred Schwarzschild radii.

Clumps are torn sheet shapes rotating with sub-Keplerian velocities.

Outflow variability timescales match some observed ultra-luminous X-ray sources.

Abstract

We perform global three-dimensional (3D) radiation-hydrodynamic (RHD) simulations of out- flow from supercritical accretion flow around a 10 Msun black hole. We only solve the outflow part, starting from the axisymmetric 2D simulation data in a nearly steady state but with small perturbations in a sinusoidal form being added in the azimuthal direction. The mass accretion rate onto the black hole is ~10^2 L_E/c^2 in the underlying 2D simulation data and the outflow rate is ~10 L_E/c^2 (with LE and c being the Eddington luminosity and speed of light, respectively). We first confirm the emergence of clumpy outflow, which was discovered by the 2D RHD simulations, above the photosphere located at a few hundreds of Schwarzschild radii (r_S) from the central black hole. As prominent 3D features we find that the clumps have the shape of a torn sheet, rather than a cut string, and that they are rotating around the central black hole with a sub-Keplerian velocity at a distance of ~10^3 r_S from the center. The typical clump size is ~30 r_S or less in the radial direction, and is more elongated in the angular directions, ~hundreds of r_S at most. The sheet separation ranges from 50 to 150 r_S. We expect stochastic time variations when clumps pass across the line of the sight of a distant observer. Variation timescales are estimated to be several seconds for a black hole with mass of ten to several tens of Msun, in rough agreement with the observations of some ultra-luminous X-ray sources.