Formation and survivability of massive giant planets and brown dwarfs on wide orbits

We present numerical hydrodynamics simulations showing the formation and survival of giant planets and brown dwarfs on extremely wide orbits (50-500 AU) around young solar-type stars via disk gravitational fragmentation. Fragments form at distances where gravitational fragmentation is allowed (50--300 AU), but most fragments do not survive and either migrate onto the forming star or get ejected into the intracluster medium via many-body interactions. The fragments that form near the end of the embedded phase, when torques from spiral arms become weaker and the probability of close encounters becomes smaller, may survive and mature into massive gas giants or brown dwarfs on wide orbits. The number of survived fragments is one to ten at best, in agreement with a small number of such detected objects. This phenomenon can explain the existence of massive exoplanets and brown dwarfs on wide orbits is such systems as Fomalhaut, HR 8799, and HIP 78530.