3 research outputs found
Flow Morphology of a Supersonic Gravitating Sphere
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, , relative to its accretion radius, . 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 . Thus we present new 3-D Athena++ hydrodynamic
calculations for a large range of parameters. For , 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 , 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 , 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 . That exploration also reveals the minimum size of the simulation
domain needed to accurately capture the deflection of incoming streamlines due
to gravity.Comment: 18 pages, 20 figures, accepted to MNRA