The formation of stars and planets

Planet FormationTopic:

Dust motion andcoagulation

Lecture by: C.P. Dullemond1Coagulation as the start of planet formation1m1mm1m1km1000kmGravitykeeps/pullsbodiestogetherGas isaccretedAggregation(=coagulation)

First growth phaseFinal phase

Unclear if coagulation (=aggregation) isdominant up to >km size planetesimalsCoagulation dominatesthe growth of smallparticlesCoagulation: What it is...xthit and stick...if we look at a single pair of colliding particles:Collision & sticking of monomers leads to a diamerwhich is a small aggregateCoagulation: What it is...xthit and stick...if we look at a single pair of colliding particles:Collision & sticking of aggregates leadsto larger aggregates.Coagulation: What it is...xthit and stick...if we look at a single pair of colliding particles:Such aggregate-aggregate collisionsleads to fluffy aggregatesCoagulation is driven by particle motion

Part 1: Stochastic motions:Brownian Motion and TurbulenceRelative velocities between particlesCoagulation requires relative velocities between particles, so that they can hit and stick:stochastic motions due to Brownian motion and turbulent stirringsystematic relative velocities due to particle driftBrownian motion:

The smallest particles move the fastest, and dominatethe collision rate. Turbulent stirringTurbulence can induce stochastic motions of particles.To compute this, we must first understand friction between dust and gas......and for this we must understand a few things about the Maxwell-Boltzmann distribution of the gas.

So hold on a moment as we discuss friction...Maxwell-Boltzmann distributionWhen we speak about average gas particle velocity it can havemany different meanings, depending on how you do the averaging:

Friction between a particle and the gasTake a spherical dust particle with radius a and material density sEpstein drag regime = a