Rapid clump formation in discs of young stellar objects class O-I

The formation of planetesimals and large bodies in circumstellar discs can be referred to the stage of massive unstable disc emerging due to the gravitational collapse in the molecular cloud. We have simulated the dynamics of gas and boulder clumps in such systems. The features of instability development in massive disc is discussed. Unlike medium-massive discs the massive disc can provide conditions for simultaneous formation of several clumps as a result of overdensity ring fragmentation. We found regimes where 3, 2 or 1 overdensity ring appear in the disc and then fragment into clumps collecting about a half of the disc mass.