2024/02/15 by Logan J. Prust, Hila Glanz, Prust, Logan J. +7 · 3 citations
Engineering · Mathematics · #Computational Fluid Dynamics and Aerodynamics #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Fluid Dynamics and Turbulent Flows #Gas Dynamics and Kinetic Theory #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · pdf · doi:10.48550/arxiv.2402.10341
openalex publication_date 2024/02/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/03
We carry out three-dimensional computations of the accretion rate onto an object (of size R\rm sink and mass m) as it moves through a uniform medium at a subsonic speed v∞. The object is treated as a fully-absorbing boundary (e.g. a black hole). In contrast to early conjectures, we show that when R\rm sink≪ RA=2Gm/v2 the accretion rate is independent of v∞ and only depends on the entropy of the ambient medium, its adiabatic index, and m. Our numerical simulations are conducted using two different numerical schemes via the Athena++ and Arepo hydrodynamics solvers, which reach nearly identical steady-state solutions. We find that pressure gradients generated by the isentropic compression of the flow near the accretor are sufficient to suspend much of the surrounding gas in a near-hydrostatic equilibrium, just as predicted from the spherical Bondi-Hoyle calculation. Indeed, the accretion rates for steady flow match the Bondi-Hoyle rate, and are indicative of isentropic flow for subsonic motion where no shocks occur. We also find that the accretion drag may be predicted using the Safronov number, Θ=RA/R\rm sink, and is much less than the dynamical friction for sufficiently small accretors (R\rm sink≪ RA).