Influence of the circumbinary disk gravity on planetesimal accumulation in the Kepler 16 system

TL;DR

This study investigates how the gravity of an eccentric circumbinary disk influences planetesimal accumulation, revealing that disk gravity excites eccentricities and prevents alignment, thus hindering planet formation close to the stars.

Contribution

The paper introduces a hybrid hydrodynamical and N-body simulation approach to analyze the impact of disk gravity on planetesimal dynamics in circumbinary systems, highlighting effects previously unaccounted for.

Findings

Disk gravity excites planetesimal eccentricities beyond binary perturbation effects.

Large impact velocities hinder planetesimal accumulation near the binary.

Planets likely form in outer disk regions and migrate inward.

Abstract

Recent observations from NASA's Kepler mission detected the first planets in circumbinary orbits. The question we try to answer is where these planets formed in the circumbinary disk and how far inside they migrated to reach their present location. We investigate the first and more delicate phase of planet formation when planetesimals accumulate to form planetary embryos. We use the hydrodynamical code FARGO to study the evolution of the disk and of a test population of planetesimals embedded in it. With this hybrid hydrodynamical--N--body code we can properly account for the gas drag force on the planetesimals and for the gravitational force of the disk on them. The numerical simulations show that the gravity of the eccentric disk on the planetesimal swarm excites their eccentricities to values much larger than those induced by the binary perturbations only within 10 AU from the stars. Moreover, the disk gravity prevents a full alignment of the planetesimal pericenters. Both these effects lead to large impact velocities, beyond the critical value for erosion. Planetesimals accumulation in circumbinary disks appears to be prevented close to the stellar pair by the gravitational perturbations of the circumbinary disk. The observed planets possibly formed in the outer regions of the disk and then migrated inside by tidal interaction with the disk.