Morphology and Mach Number Dependence of Subsonic Bondi-Hoyle Accretion
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arXiv
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2024
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| author | Prust, Logan J. Glanz, Hila Bildsten, Lars Perets, Hagai B. Roepke, Friedrich K. |
| author_facet | Prust, Logan J. Glanz, Hila Bildsten, Lars Perets, Hagai B. Roepke, Friedrich K. |
| contents | 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 $v_{\infty}$. The object is treated as a fully-absorbing boundary (e.g. a black hole). In contrast to early conjectures, we show that when $R_{\rm sink}\ll R_{A}=2Gm/v^2$ the accretion rate is independent of $v_{\infty}$ 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, $Θ=R_{A}/R_{\rm sink}$, and is much less than the dynamical friction for sufficiently small accretors ($R_{\rm sink}\ll R_{A}$). |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2402_10341 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Morphology and Mach Number Dependence of Subsonic Bondi-Hoyle Accretion Prust, Logan J. Glanz, Hila Bildsten, Lars Perets, Hagai B. Roepke, Friedrich K. High Energy Astrophysical Phenomena Fluid Dynamics 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 $v_{\infty}$. The object is treated as a fully-absorbing boundary (e.g. a black hole). In contrast to early conjectures, we show that when $R_{\rm sink}\ll R_{A}=2Gm/v^2$ the accretion rate is independent of $v_{\infty}$ 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, $Θ=R_{A}/R_{\rm sink}$, and is much less than the dynamical friction for sufficiently small accretors ($R_{\rm sink}\ll R_{A}$). |
| title | Morphology and Mach Number Dependence of Subsonic Bondi-Hoyle Accretion |
| topic | High Energy Astrophysical Phenomena Fluid Dynamics |
| url | https://arxiv.org/abs/2402.10341 |