Year: 2026
Type: article
Abstract: We study spherical accretion onto primordial black holes (PBHs) embedded in the core of a solar-type star. We compute the radiative efficiency self-consistently for the first time across more than 6 decades in black hole mass (10 −16.5 –10 −10 M ⊙ ) with time-dependent simulations, and follow the growth up to 10 −2 M ⊙ using an analytical photon-trapping prescription above 5 × 10 −13 M ⊙ . Near the Schwarzschild radius ( r S ∼ 10 −11 cm for a 10 −16 M ⊙ PBH), gas compressed to T ∼ 10 11 K radiates through microphysical processes that fundamentally alter the classical adiabatic Bondi solution. We solve the time-dependent spherical Euler equations with an implicit cooling source term, determining M ̇ , the Bondi-normalized radiative efficiency η = L / ( M ̇ B c 2 ) , and the flow structure self-consistently. We identify three regimes for spherical accretion: a hot Bondi regime ( M BH ≲ 10 −14 M ⊙ ) in which bremsstrahlung cooling is dynamically negligible; a bremsstrahlung-cooling regime (10 −14 –5 × 10 −13 M ⊙ ) driving the flow toward isothermal with η ≈ 10 −2 ; and a photon-trapping regime above 5 × 10 −13 M ⊙ , in which the Bondi sphere is optically thick and the accretion rate remains close to the Bondi value. Cooling enhances M ̇ by a factor of ∼1.5–7, keeping growth superexponential throughout the spherical regime. The radiative efficiency is an order of magnitude lower than previously assumed, and the critical initial PBH mass required to consume a solar-mass star within a Hubble time is M 0,crit ∼ 10 −16 M ⊙ .
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W7163405477