NONLINEAR DYNAMICAL FRICTION OF A CIRCULAR-ORBIT PERTURBER IN A GASEOUS MEDIUM
- Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of)
We use three-dimensional hydrodynamic simulations to investigate the nonlinear gravitational responses of gas to, and the resulting drag forces on, very massive perturbers moving in circular orbits. This work extends our previous studies that explored the cases of low-mass perturbers in circular orbits and massive perturbers on straight-line trajectories. The background medium is assumed to be non-rotating, adiabatic with index 5/3, and uniform with density {rho}{sub 0} and sound speed a{sub 0}. We model the gravitating perturber using a Plummer sphere with mass M{sub p} and softening radius r{sub s} in a uniform circular motion at speed V{sub p} and orbital radius R{sub p} , and run various models with differing R{identical_to}r{sub s}/R{sub p}, M{identical_to}V{sub p}/a{sub 0}, and B{identical_to}GM{sub p}/(a{sub 0}{sup 2}R{sub p}). A quasi-steady density wake of a supersonic model consists of a hydrostatic envelope surrounding the perturber, an upstream bow shock, and a trailing low-density region. The continuous change in the direction of the perturber motion reduces the detached shock distance compared to the linear-trajectory cases, while the orbit-averaged gravity of the perturber gathers the gas toward the center of the orbit, modifying the background preshock density to {rho}{sub 1}{approx}(1+0.46B{sup 1.1}){rho}{sub 0} depending weakly on M. For sufficiently massive perturbers, the presence of a hydrostatic envelope makes the drag force smaller than the prediction of the linear perturbation theory, resulting in F=4{pi}{rho}{sub 1}(GM{sub p})?2/V{sub p}?2 x (0.7{eta}{sub B}?-?1) for {eta}{sub B{identical_to}}B/(M?2-1)>0.1; the drag force for low-mass perturbers with {eta}{sub B}<0.1 agrees well with the linear prediction. The nonlinear drag force becomes independent of R as long as R<{eta}{sub B}/2, which places an upper limit on the perturber size for accurate evaluation of the drag force in numerical simulations.
- OSTI ID:
- 21474362
- Journal Information:
- Astrophysical Journal, Vol. 725, Issue 1; Other Information: DOI: 10.1088/0004-637X/725/1/1069; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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