Abstract: In collisional mechanisms of planetesimal formation ‘bouncing barrier’ and ‘drift barrier’ are well-known. Local gravitational collapses of solids are studied by several groups as a way to get over such barriers. Possibility of local gravitational collapses of solids depends on the local velocity dispersion of solids. Main mechanisms to regulate the velocity dispersion of solids in massive unstable discs of YSO class O-I are drag (decreases the dispersion) and interaction between solids and peaks of gravitational potential of the disc (can increase and decrease the dispersion). Results of Lodato et al. MNRAS 2006, Gibbons et al. MNRAS 2014 demonstrates that 50-cm boulders are collected by the spiral arms of massive circumstellar disc most efficiently. We simulate the dynamics of 100-1000 cm-sized solids in massive circumstellar disc with Toomre parameter Q <1. In such regime of disc dynamics solitary clumps of and boulders are formed due to the development of gravitational instability. In contrast with the spirals the gravitational peaks of such clumps are powerful enough to provide the efficient capturing of solids even without regards of gas drag. It makes such clumps excellent areas where planetesimal-sized objects can be formed rapidly. On the other hand another phenomenon is important. Despite of powerful gas drag some 100cm-sized boulders in massive unstable discs were found to be wandering, it means that they were captured by one clump, than ejected and captured by the next clump. Such wandering boulders can provide efficient species transport between clumps and from clump to disc atmosphere as well as play a role in chondrule formation due to providing rapidly changing physical conditions for matter.

Cite: Stoyanovskaya O.P.
Collective Dynamics of Boulders in Unstable Discs of Young Stellar Objects Class O-I
Second Workshop "The Formation of the Solar System" 02-04 Jun 2015