Hydro HD calculates the fluid flow in an accretion disc around a star in real time on your iPad.
Each newly formed star has such an accretion disc. It is made out of dense gas and dust. The disc forms because of the conservation of angular momentum. The nebular hypothesis of solar system formation describes how accretion discs are thought to evolve into planetary systems. The formation of planets within this disc is the reason why the planets in our solar system are arranged in an ecliptic plane.
The interested user may enjoy a detailed description of the algorithm that is used in this application.