What velocity limit causes the fragmentation barrier for silicate aggregates?
Low collision velocities, typically less than 1 m/s.
The initial growth phase in the bottom-up approach requires microscopic dust grains to stick together to form larger intermediate solids, eventually leading to planetesimals. However, laboratory experiments reveal a physical limitation known as the fragmentation barrier. Silicate aggregates, when colliding, can only maintain structural integrity and stick together if the collision velocity remains quite low, specifically documented as being typically under 1 meter per second. In the turbulent environment of a protoplanetary disk, collision speeds quickly surpass this threshold. When particles collide faster than this limit, they shatter rather than coagulate, thereby preventing the growth of larger solid bodies through simple sticking mechanisms.
