Abstract

Large-scale vortices in protoplanetary disks are expected to form and survive for long periods of time in accordance with disk asymmetries observed in the sub-mm and mm wavelength ranges. Such vortices are known to trap in their core large amounts of dust grains that we assume to agglomerate into big boulders weakly coupled to the gas. Aims. The dynamics and growth of the boulders is explored when the vortex is located at 50AU from the star, a region of the disk where self-gravity plays a significant role. Methods. Global 2D simulations are used to follow boulder dynamics in the star+disk gravitational field. Collisional evolution of the boulders is discussed and traced on the standard coagulation scenario. Results. When released by the core, the boulders accumulate in the co-orbital region associated to the vortex where they stay confined in a domain that shrinks radially due to gas drag. The increased density and the low velocity-dispersion favour the coagulation of the boulders that reach the kilometer-size range in some thousands orbital periods. After the vortex death, the evolution continues following the standard scenario. Conclusions. Besides their ability to capture and accumulate dust-grains in their core large-scale vortices can also confine boulder-size particles in their co-orbital region. Trapped boulders can grow into km-size planetesimals possibly explaining the formation of Cold Classical Kuiper-Belt Objects (CC-KBOs)