Polar circumtriple planets and disks can only form close to a triple star

TL;DR

This paper investigates the formation of polar circumtriple disks and planets around triple star systems, finding they can only form close to the stars due to dynamical effects, with potential implications for observed systems.

Contribution

It introduces the concept that polar circumtriple disks and planets are confined to regions close to the stellar system, considering the effects of the third star and apsidal precession.

Findings

Polar circumtriple disks are limited to within 3-10 times the binary separation.

Outside the critical radius, orbits behave like around a circular binary.

Shorter period inner binaries increase the critical radius.

Abstract

Observations of protoplanetary disks around binary and triple star systems suggest that misalignments between the orbital plane of the stars and the disks are common. Motivated by recent observations of polar circumbinary disks, we explore the possibility for polar circumtriple disks and therefore polar circumtriple planets that could form in such a disk. With n-body simulations and analytic methods we find that the inclusion of the third star, and the associated apsidal precession, significantly reduces the radial range of polar orbits so that circumtriple polar disks and planets can only be found close to the stellar system. Outside of a critical radius, that is typically in the range of 3-10 times the outer binary separation depending upon the binary parameters, the orbits behave the same as they do around a circular orbit binary. For some observed systems that have shorter period inner binaries, the critical radius is considerably larger. If polar circumtriple planets can form, we suggest that it is likely that they form in a disk that was subject to breaking.