Accretion of gas onto gap-opening planets and circumplanetary flow structure in magnetized turbulent disks

Abstract

We have performed three-dimensional magneto-hydrodynamical simulations of stellar accretion disks, using the PLUTO code, and studied the accretion of gas onto a Jupiter-mass planet and the structure of the circumplanetary gas flow after opening a gap in the disk. We compare our results with simulations of laminar, yet viscous disks with different levels of an $\alpha$-type viscosity. In all cases, we find that the accretion flow across the surface of the Hill sphere of the planet is not spherically or azimuthally symmetric, and is predominantly restricted to the mid-plane region of the disk. Even in the turbulent case, we find no significant vertical flow of mass into the Hill sphere. The outer parts of the circumplanetary disk are shown to rotate significantly below Keplerian speed, independent of viscosity, while the circumplanetary disk density (therefore the angular momentum) increases with viscosity. For a simulation of a magnetized turbulent disk, where the global averaged alpha stress is $\alpha_{MHD}=10^{-3}$, we find the accretion rate onto the planet to be $\dot{M}\approx 2\times10^{-6}M_{J}yr^{-1}$ for a gap surface density of $12 g cm^{-2}$. This is about a third of the accretion rate obtained in a laminar viscous simulation with equivalent $\alpha$ parameter.