Eccentricity evolution in gaseous dynamical friction

ABSTRACT We analyse how drag forces modify the orbits of objects moving through extended gaseous distributions. consider hydrodynamic (surface area) and dynamical friction (gravitational) drive evolution orbital eccentricity. While cause eccentric to become more circular, can eccentric. develop a semi-analytic model that accurately predicts these changes by comparing total work torque applied orbit at periapse apoapse. use toy radial power-law density profile, ρ ∝ r−γ, determine there is critical γ = 3 power index, which separates eccentricity in friction: for < circularize > 3. apply findings infall Jupiter-like planet into envelope its host star. The hydrostatic envelopes stars are defined steep gradients near limb shallower interior. Under influence friction, an infalling object’s will first decrease then increase. separation delineates regimes predicted local slope linearly dependent on polytropic index. More broadly, our indicate binary systems may routinely emerge from common phases with non-zero eccentricities were excited drove their tightening.