Growth and form of two-dimensional rotating aggregates.

We propose a two-dimensional particle-cluster aggregation model which considers explicitly linear and angular momentum conservation. Each aggregate is grown from a seed of given mass and given initial angular velocity, to which particles of unitary mass and ballistic trajectories are added. The fractal dimensions of the resulting aggregates are calculated and Fourier transform analysis is performed. Very different features are found, as initial conditions are varied. Particularly, spiral structures are found for a seed of high mass and high initial angular velocity.