Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2B090

Planetesimal formation by sweep-up coagulation

Windmark, Fredrik (Center for Astronomy, Institute for Theoretical Astrophysics, Heidelberg University)
Birnstiel, Til (Harvard-Smithsonian Center for Astrophysics, Cambridge)
Ormel, Chris W. (University of California, Berkeley)
Dullemond, Cornelis P. (Center for Astronomy, Institute for Theoretical Astrophysics, Heidelberg University)

The formation of planetesimals is often accredited to collisional sticking of dust grains in the protoplanetary disk. The exact process is however unknown, as collisions between larger aggregates tend to lead to fragmentation or bouncing rather than sticking. These growth barriers tend to halt the dust growth already at millimeters or centimeters in size, which is far below the kilometer-sizes that are needed for gravity to aid in the accretion. To study how far dust coagulation can proceed, we have developed a new collision model based on the latest laboratory experiments, and have used it together with a dust-size evolution code capable of resolving all grain interactions in the protoplanetary disk. We find that for the general dust population, bouncing and fragmenting collisions prevent the growth above millimeter-sizes. However, a small number of lucky particles can grow larger than the rest by only interacting at low, sticky velocities. As they grow, they become increasingly resilient to fragmentation caused by the small grains. In this way, two populations are formed: One which remains small due to the collisional barriers, and one that continues to grow by sweeping up the smaller grains around them.

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