Gas giant protoplanets formed by disk instability in binary star systems

Gas giant planets have been discovered in binary or triple star systems with a range of semimajor axes. We present a new suite of three-dimensional radiative gravitational hydrodynamics models suggesting that binary stars may be quite capable of forming planetary systems similar to our own. One difference between the new and previous calculations is the inclusion of artificial viscosity in the previous work, leading to significant conversion of disk kinetic energy into thermal energy in shock fronts and elsewhere. New models are presented showing how vigorous artificial viscosity can help to suppress clump formation. The new models with binary companions do not employ any explicit artificial viscosity and also include the third (vertical) dimension in the hydrodynamic calculations, allowing for transient phases of convective cooling. The new calculations of the evolution of initially marginally gravitationally stable disks show that the presence of a binary star companion may actually help to trigger the formation of dense clumps that could become giant planets. Earth-like planets would form much later in the inner disk regions by the traditional collisional accumulation of progressively larger, solid bodies. We also show that in models without binary companions, which begin their evolution as gravitationally stable disks, the disks evolve to form dense rings, which then break up into self-gravitating clumps. The latter models suggest that the evolution of any self-gravitating disk with sufficient mass to form gas giant planets is likely to lead to a period of disk instability, even in the absence of a trigger such as a binary star companion.