Biconical-dominated Accretion Flow onto Seed Black Holes in a
  Hyper-accretion Regime
  Hyperaccretion 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 hyperaccretion flows; however, the sustainability of such structures 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 nonuniform accretion flow can lead to the formation of a rotating gas disk
around the BH. Once the disk forms, the supply of gas to the BH preferentially
occurs via biconical-dominated accretion flow perpendicular to the disk,
avoiding the centrifugal barrier of the disk. Biconical-dominated accretion
flows 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
nonnegligible 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
biconical-dominated accretion flow and decretion disk continues to provide
uninterrupted flow of high-density gas to the BH.
