# Polar alignment of a protoplanetary disk around an eccentric binary

## TL;DR

This study demonstrates through hydrodynamical simulations that circumbinary disks around eccentric binaries can evolve from misaligned to polar orientations, affecting planet formation processes.

## Contribution

It reveals the mechanism and conditions under which misaligned disks around eccentric binaries become polar, a novel insight into disk evolution.

## Key findings

- Disks can evolve to polar orientation via nodal libration and damping.
- Critical initial tilt angle depends on binary eccentricity and disk mass.
- Process occurs for disks less than a few percent of binary mass with initial tilt >40°.

## Abstract

We use three-dimensional hydrodynamical simulations to show that an initially mildly misaligned circumbinary accretion disk around an eccentric binary can evolve to an orientation that is perpendicular to the orbital plane of the binary (polar alignment). As the disk evolves to the perpendicular state, it undergoes nodal libration oscillations of the tilt angle and the longitude of the ascending node. Dissipation within the disk causes the oscillations to damp. The process operates above a critical initial misalignment angle that depends upon the eccentricity of the binary and the mass of the disk. For binary eccentricity of 0.5, the process operates typically for disk masses smaller than a few percent of the binary mass and initial tilt angle of more than 40 degrees. This evolution has important implications for planet formation around eccentric binary star systems.