SOLAR SYSTEM

Detailed explanation-1: -A protostar becomes a star when nuclear fusion begins. Most likely the next step was that the nebula flattened into a disk called the Protoplanetary Disk; planets eventually formed from and in this disk. Three processes occurred with the nebular collapse: Temperatures continued to increase.

Detailed explanation-2: -Summary: Stars form in cold, dense regions of space called molecular clouds. When the force of gravity pulling in on the cloud is greater than the strength of internal pressure pushing out, the cloud collapses into a protostar.

Detailed explanation-3: -A shock wave from a nearby supernova explosion probably initiated the collapse of the solar nebula.

Detailed explanation-4: -The nebular hypothesis is the idea that a spinning cloud of dust made of mostly light elements, called a nebula, flattened into a protoplanetary disk, and became a solar system consisting of a star with orbiting planets [12].