Since the PSN is rotating, centrifugal force prevents some gas from reaching the forming star. This gas forms a flattened disk around the protostar. Click to enlarge images. As PNS collapses, it heats up enough for the dust to vaporize. Initial collapse takes less than 100,000 years.
Disk radiates away energy and cools off.
Instabilities in the collapsing, rotating cloud cause local regions to begin to contract gravitationally. Large concentrations of gas orbiting the protostar may be unstable and gravitationally collapse to form a double star. Smaller local regions of condensation form proto-planets by accretion of planetesimals. Accretion continues until the particles get to the size of boulders or small asteroids. Click on the images below to enlarge them.