Gravitational Instability in Planetesimal Disks

Bryce Bolin, Institute For Astrophysics, Hawaii
Advisors: Yoram Lithwick, Margaret Pan, Yanqin Wu

Abstract: Gravitational instability (GI) has been proposed as a method of form- ing giant gas planets enhanced by disk thermodynamics in a protoplan- etary disk (Durisen et al. 2007; Boss 1997) and as a method of forming planetesimals through the focusing of boulders by the interaction be- tween solids and gases in a turbulent circumstellar disk (Johansen et al. 2007; Youdin and Goodman 2005). GI is mediated through a gaseous circumstellar disk in each each of these scenarios. We explore the pos- sibility of GI occurring in a planetesimal disk devoid of gas. In this regime, mutual collisions between planetesimals are required to dissipate their orbital shear and velocity dispersion enough for collapse to occur as described by the Toomre stability criterion (Goldreich and Lynden-Bell 1965; Toomre 1964). How frequent must collisions be between planetes- imals in a gravitationally stable planetesimal disk for GI to occur? Are there collisional rates where GI is postponed indefinitely in an equilibrium state between gravitational stirring and collisional cooling? We present 3D shearing sheet simulations using the REBOUND N-body code with the symplectic epicyclic integrator (Rein and Liu (2012); ?) in which the candidate collision rates are within a few orders of magnitude of the disk dynamical lifetime. Our simulations suggest that collisions rate directly controls disk cooling. The shape of the disk cooling curve is independent of the collision rate when scaled to the collision time.

PDF Presentation
Project report