Gravitational instability in binary protoplanetary disks; new constraints on giant planet formation

Abstract

We use high resolution 3D SPH simulations to study the evolution of self-gravitating binary protoplanetary disks. Heating by shocks and cooling are included. We consider different orbital separations and masses of the disks and central stars. Isolated massive disks ($M \sim 0.1 M_{ødot}$) fragment into protoplanets as a result of gravitational instability for cooling times comparable to the orbital time. Fragmentation does not occur in binary systems with a separation of about 60 AU. This is because efficient heating owing to strong tidally induced spiral shocks damps any overdensity. The resulting temperatures, above 200 K, would vaporize water ice in the outer disk, posing a problem even for the other model of giant planet formation, core-accretion. Light disks ($M \sim 0.01 M_{\odot}$) do not fragment but remain cold because their low self-gravity inhibits strong shocks. Core accretion would not be hampered in the latter. At separations of about 120 AU the efficiency of fragmentation by disk instability rises and approaches that in isolated systems. If disk instability is the main formation mechanism for giant planets, on going surveys targeting binary systems should find considerably fewer planets in systems with separations below 100 AU.