Title: Radially resolved simulations of collapsing pebble clouds in protoplanetary discs,
Abstract: We study the collapse of pebble clouds with a statistical model to find the
internal structure of comet-sized planetesimals. Pebble-pebble collisions occur
during the collapse and the outcome of these collisions affect the resulting
structure of the planetesimal. We expand our previous models by allowing the
individual pebble sub-clouds to contract at different rates and by including
the effect of gas drag on the contraction speed and in energy dissipation. Our
results yield comets that are porous pebble-piles with particle sizes varying
with depth. In the surface layers there is a mixture of primordial pebbles and
pebble fragments. The interior, on the other hand, consists only of primordial
pebbles with a narrower size distribution, yielding higher porosity there. Our
results imply that the gas in the protoplanetary disc plays an important role
in determining the radial distribution of pebble sizes and porosity inside
planetesimals.