MPEG movies of collisions between dust aggregates

The page you are currently viewing contains only a selection of the calculations we have done (the ones discussed in the paper). If this is not enough for you, a more extensive version can be found here.

This page contains links to a number of MPEG video streams showing the collision between dust aggregates as discussed in the paper by Dominik and Tielens: The physics of dust coagulation and the structure of dust aggregates in space, submitted to the Astrophysical Journal.

The code used to model the collisions is a 2D N-particle code. The physics of each grain and contact is treated in great detail and resolved in the calculations down to individual vibrations of grains in contact around the equilibrium position. The physics of contacts is discussed in three papers:

Chokshi, Tielens, Hollenbach, 1993, Astrophysical Journal 407, page 806

Dominik, Tielens, 1995, Philosophical Magazine A 72, page 783

Dominik, Tielens, 1996, Philosophical Magazine A 73, page 1279

Here are a few examples of collisions. Each movie shows the collision of an aggregate of dust grains with either another aggregate or a single grain at many different velocities. The MPEG files are typically about 1 MByte each - so I recommend a fast line, or a cup of coffee.

Collisions between an aggregate and a small grain

In these calculations, the aggregate is made of identical grains. A similar grain (same size and material) impacts the aggregate at different speeds. It can be seen, that at small velocities, the grain simply sticks to the aggregate. At intermediate velocities, a small amount of restructuring is going on near the impact point. High velocities break the aggregate into individual grains.

View Movie Grain material: H2O ice Particle radii: 1E-5cm Velocities: 200..100000cm/s

The strength of a contact is a function of the material properties. The following movie is similar to the on shown above, but the grain material is quartz, which binds much weaker. Consequently, destruction of the aggregate already happens at much lower velocities.

View Movie Grain material: Quartz Particle radii: 1E-5 cm Velocities: 50..5000cm/s

Smaller grains bind stronger relative to their mass. Thus, in the following collisions with small icy grains, destruction only starts at very high velocities.

View Movie Grain material: H2O ice Particle radii: 1E-6 cm Velocities: 1000..100000cm/s

In the following collision, the aggregate is made of grains with a range of sizes. We did these calculations in order to show, that the effective destruction of aggregates in the cases with only a single grain size is not entirely a resonance effect.

View Movie Grain material: H2O ice Particle radii: 5E-6...2E-5 cm Impactor radius: 1E-5 cm Velocities: 500..100000cm/s

Collision of a Core-Mantle grain with a single grain

These calculation feature a core-mantle aggregate: An aggregate dominated by one very large grain, with smaller grains attached to its surface. As long as the impactor is much smaller than the large grain in the aggregate, damage is only done near the impact site. Grains on the opposite side of the aggregate are unaffected. This is mainly due to the low efficiency of energy transfer from the small impactor to the large grain.

View Movie Grain material: H2O ice Particle radii: 1E-5 cm Impactor radius: 2E-6 cm Velocities: 500..100000cm/s

Collision of an aggregate with a large grain

Differently from the impacts of small grains discussed above, impacts of large grains can considerably compress an aggregate without destroying it.

View Movie Grain material: H2O ice Particle radii: 1E-5 cm Impactor radius: 2E-5 cm Velocities: 200..20000cm/s

View Movie Grain material: H2O ice Particle radii: 1E-5 cm Impactor radius: 1E-4 cm Velocities: 50..10000cm/s

Collisions between two identical aggregates

Here, two identical aggregates, each made of 40 identical particles, collide at different speeds. Again, like in the impacts with large grains, considerable restructuring and compaction is possible.

View Movie Grain material: H2O ice Particle radii: 1E-5 cm Velocities: 100..20000cm/s