Kavli Affiliate: Lars Bildsten
| First 5 Authors: Logan J. Prust, Lars Bildsten, , ,
| Summary:
Stars and planets move supersonically in a gaseous medium during planetary
engulfment, stellar interactions and within protoplanetary disks. For a nearly
uniform medium, the relevant parameters are the Mach number and the size of the
body, $R$, relative to its accretion radius, $R_A$. Over many decades,
numerical and analytical work has characterized the flow, the drag on the body
and the possible suite of instabilities. Only a limited amount of work has
treated the stellar boundary as it is in many of these astrophysical settings,
a hard sphere at $R$. Thus we present new 3-D Athena++ hydrodynamic
calculations for a large range of parameters. For $R_All R$, the results are
as expected for pure hydrodynamics with minimal impact from gravity, which we
verify by comparing to experimental wind tunnel data in air. When $R_Aapprox
R$, a hydrostatically-supported separation bubble forms behind the gravitating
body, exerting significant pressure on the sphere and driving a recompression
shock which intersects with the bow shock. For $R_Agg R$, the bubble
transitions into an isentropic, spherically-symmetric halo, as seen in earlier
works. These two distinct regimes of flow morphology may be treated separately
in terms of their shock stand-off distance and drag coefficients. Most
importantly for astrophysical applications, we propose a new formula for the
dynamical friction which depends on the ratio of the shock stand-off distance
to $R_A$. That exploration also reveals the minimum size of the simulation
domain needed to accurately capture the deflection of incoming streamlines due
to gravity.
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