Physical length scales controlling the accretion regime as a function of PBH mass, for solar-core conditions. The Bondi radius r_B (blue) defines the gravitational sphere of influence. The vertical dotted line marks τ(r_B) = 1, where the Bondi sphere becomes optically thick (M ∼ 5 × 10⁻¹³ M_⊙). The photon-trapping radius r_trap (red) exceeds r_B at M ∼ 10⁻⁹ M_⊙. Two circularization radii r_circ (orange) are shown: one for the present-day solar-core rotation (Ω/Ω_br ≈ 5 × 10⁻⁴, solid) and one for 10% of the core breakup frequency ﹩{{\rm{\Omega }}}_{{\rm{br}}}=\sqrt{G{M}_{{\rm{core}}}/{r}_{{\rm{core}}}^{3}}\approx 5.3\times 1{0}^{-3}﹩ rad s⁻¹ (dashed). An accretion disk forms where r_circ crosses r_ISCO (black dashed). Young solar-type stars rotate significantly faster than the present Sun, so disk formation may occur at lower BH masses during the early evolution. Colored bands denote the three spherical-accretion regimes discussed in Section 3.1; the onset of trapping at τ(r_B) = 1 marks the boundary into the photon-trapping regime. The two horizontal dotted lines mark the photon mean free path in the unperturbed solar core, ℓ_mfp = 1/(n_eσ_T) ≈ 0.025 cm (green), and the pressure scale height of the solar core, H_P ≈ 7.9 × 10⁹ cm (purple), above which the ambient stellar stratification becomes relevant.