Accretion of Active Galactic Nucleus Stars Under the Influence of Disk Geometry

Massive stars can form within or be captured by active galactic nucleus disks, influencing both the thermal structure and metallicity of the disk environment. In a previous work, we investigated isotropic accretion onto massive stars from a gas-rich, high-entropy background. Here, we consider a more realistic scenario, by incorporating the stratified geometry of the background disk in our 3D radiation hydrodynamic simulations. We find that the accretion remains relatively isotropic when the disk is hot enough and the scale height is thicker than the accretion flow’s nominal supersonic critical radius R_crit (subthermal). However, when the disk becomes cold, the accretion flow becomes significantly anisotropic (superthermal). Escaping stellar and accretion luminosity can drive super-Eddington outflows in the polar region, while rapid accretion is sustained along the midplane. Eventually, the effective cross section is constrained by the Hill radius and the disk scale height rather than the critical radius when the disk is cold enough. For our setup (stellar mass ∼50 M_⊙ and background density ρ ∼ 10⁻¹⁰ g cm⁻³), the accretion rate is capped below ∼0.02M_⊙ yr⁻¹ and the effective accretion parameter α ∼ 10⁻¹ over the disk temperature range 3-7 × 10⁴ K. Spiral arms facilitate inward mass flux by driving outward angular momentum transport. Gap-opening effects may further reduce the long-term accretion rate, although to confirm this would require global simulations evolved over much longer viscous timescales.