A fast-growing tilt instability of detached circumplanetary disks

TL;DR

This paper investigates a rapid tilt instability in detached circumplanetary disks, showing that such disks can become significantly misaligned with the planetary orbital plane within a few binary orbits, impacting planetary spin and dynamics.

Contribution

The study identifies conditions under which tilt instability occurs in circumplanetary disks and quantifies its growth rate using both linear analysis and hydrodynamic simulations.

Findings

Tilt instability can cause disks to double their tilt in 15-30 binary orbits.

Detached circumplanetary disks are likely to be misaligned with planetary orbits.

Implications for planetary spin evolution and interactions with Kozai-Lidov dynamics.

Abstract

Accretion disks in binary systems can exhibit a tilt instability, arising from the interaction between components of the tidal potential and dissipation. Using a linear analysis, we show that the aspect ratios and outer radii of circumplanetary disks provide favorable conditions for tilt growth. We quantify the growth rate of the instability using particle-based ({\sc phantom}) and grid-based ({\sc athena++}) hydrodynamic simulations. For a disk with outer aspect ratio $H/r \simeq 0.1$, initially moderate tilts double on a time scale of about 15-30 binary orbits. Our results imply that detached circumplanetary disks, whose evolution is not entirely controlled by accretion from the circumstellar disk, may commonly be misaligned to the planetary orbital plane. We discuss implications for planetary spin evolution, and possible interactions between the tilt instability and Kozai-Lidov dynamics.