Spiral patterns in planetesimal circumbinary disks

TL;DR

This paper develops a secular theory for planetesimal dynamics in circumbinary disks, revealing transient spiral density waves that depend on binary eccentricity and mass ratio, with implications for understanding young planetary systems.

Contribution

It introduces a new analytical model for spiral patterns in planetesimal disks around eccentric binaries, validated by numerical simulations, especially in gas-free conditions.

Findings

Spiral density waves form in circumbinary disks with eccentric binaries.

The spiral pattern is transient and indicates a young system.

Residual gas affects wave propagation, as shown by SPH simulations.

Abstract

Planet formation scenarios and the observed planetary dynamics in binaries pose a number of theoretical challenges, especially in what concerns circumbinary planetary systems. We explore the dynamical stirring of a planetesimal circumbinary disk in the epoch when the gas component disappears. For this purpose, following theoretical approaches by Heppenheimer (1978) and Moriwaki and Nakagawa (2004), we develop a secular theory for the dynamics of planetesimals in circumbinary disks. If the binary is eccentric and its components have unequal masses, a spiral density wave is generated, engulfing the disk on the secular timescale, which may exceed 10^7 yr, depending on the problem parameters. The spiral pattern is transient; thus, its observed presence may betray system's young age. We explore the pattern both analytically and in numerical experiments. The derived analytical spiral is a modified lituus; it matches the numerical density wave in the gas-free case perfectly. Using the SPH scheme, we explore the effect of residual gas on the wave propagation.