"Can Gravitational Instabilities Produce Gas Giant Planets in Disks Around Young Stars?"

Gravitational instabilities (GI's) almost certainly occur in disks around young stars. I will review recent efforts to simulate their consequences for disk evolution. The nonlinear amplitude of the resulting non-local spiral turbulence depends on the balance of heating and cooling mechanisms in the disks. Mass transport due to gravitational torques is carried predominantly by low-order global modes. Average mass inflow rates vary inversely with disk cooling time. For short enough cooling times, disks undergo a phase transition where they fragment into dense structure. I will review the current status of efforts to determine whether or not the resulting dense clumps are permanent bound "protoplanets". Do not necessarily believe everything you read; results are sensitive to numerical methods. It remains unclear whether fragmentation due to GI's can lead directly to protoplanets under real conditions. I will also briefly discuss a hybrid scenario in which GI's accelerate formation of gas giants by core-accretion.