Polar Circumtriple Planets and Disks Can Only Form Close to a Triple Star

• Published in: Astrophysical journal. Letters Vol. 943; no. 1; p. L4
• Main Authors: Lepp, Stephen, Martin, Rebecca G., Lubow, Stephen H.
• Format: Journal Article
• Language: English
• Published: Austin The American Astronomical Society 01.01.2023; IOP Publishing
• Subjects: Accretion disks; Binary stars; Celestial mechanics; Circular orbits; Exoplanet dynamics; Extrasolar planets; Orbits; Planet formation; Planets; Polar orbits; Protoplanetary disks; Stars; Stellar systems; Trinary stars; Triple stars
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/acaf6d

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 of 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 a 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.