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Migration of dense gaseous clumps that form in young protostellar disks viagravitational fragmentation is investigated to determine the likelihood ofgiant planet formation. High-resolution numerical hydrodynamics simulations inthe thin-disk limit are employed to compute the formation and long-termevolution of a gravitationally unstable protostellar disk around a solar-massstar. We show that gaseous clumps that form in the outer regions of the disk(>100 AU) through disk fragmentation are often perturbed by other clumps ordisk structures, such as spiral arms, and migrate toward the central star ontimescales from a few 10^3 to few 10^4 yr. The migration timescale is slowestwhen stellar motion in response to the disk gravity is considered. Whenapproaching the star, the clumps first gain mass (up to several tens of M_Jup),but then quickly lose most of their diffuse envelopes through tidal torques.Part of the clump envelope can be accreted on the central star causing anFU-Ori-type accretion and luminosity outburst. The tidal mass loss helps theclumps to significantly slow down or even halt their inward migration at adistance of a few tens of AU from the protostar. The resulting clumps areheavily truncated both in mass and size compared to their wider-orbitcounterparts, keeping only a dense and hot nucleus. During the inwardmigration, the temperature in the clump interiors may exceed the molecularhydrogen dissociation limit (2000 K) and the central region of the clump cancollapse into a gas giant protoplanet. We argue that FU-Orionis-type luminosityoutbursts may be the end product of disk fragmentation and clump inwardmigration, ushering the formation of giant protoplanets on tens-of-au orbits insystems such as HR~8799.

Gravitational fragmentation and formation of giant protoplanets on tens-of-au orbits