The hot, dense center becomes a protostar. Something is missing in the theory. Dust helps collect enough matter to form planets. Planet Formation Planets form in 3 stages dust grains form condensation nuclei that begin to collect matter the larger clumps of matter begin to stick together and continue to grow until approximately 200 km across. At this stage, the objects are called planetesimals and their own gravity is big enough to attract other matter.
Planetesimals are about the size of small moons.
Gravitational forces cause the planetesimals to collide and merge until all planetesimal material is swept up into a few large protoplanets. Protoplanets continue to grow and evolve. The key is heat and chemistry - condensation of different chemicals in the dust As the nebula flattens, the center is very hot and the edges are cooler In hot regions, dust grains get split into component molecules and elements. In cold outer regions, dust remains intact The types of condensates at a given location determined what was available to the forming protoplanets. Cores were initially cold, low density, icy material Accretion began sooner because of the cooler temperatures.