Biconical dominated accretion flow onto seed black holes in hyper-accretion regime
Hyper-accretion occurs when the gas inflow rate onto a black hole (BH) is so high that the radiative feedback cannot reverse the accretion flow. This extreme process is a promising mechanism for the rapid growth of seed BHs in the early universe, which can explain high-redshift quasars powered by billion solar mass BHs. In theoretical models, spherical symmetry is commonly adopted for hyper-accretion flow, however its sustainability on timescales corresponding to the BH growth has not been addressed yet. Here we show that stochastic interactions between the ionizing radiation from the BH and non-uniform accretion flow can lead to a formation of rotating gas disk around the BH. Once the disk is formed, the supply of gas to the BH preferentially occurs via biconical dominated accretion flow (BDAF) perpendicular to the disk, avoiding the centrifugal barrier of the disk. BDAFs from opposite directions collide in the vicinity of the BH supplying high-density, low angular momentum gas to the BH, whereas most of the gas with non-negligible angular momentum is deflected to the rotationally supported outflowing decretion disk. The disk becomes reinforced progressively as more mass from the biconical flow transfers to the disk and some of the outflowing gas from the disk is redirected to the biconical accretion funnels through a meridional structure. This axisymmetric hydrodynamic structure of a BDAF and decretion disk continues to provide uninterrupted flow of high-density gas to the BH.