1. Initial Collapse:
* Trigger: The collapse was likely triggered by a nearby supernova explosion, a shock wave from a passing star, or even the gravitational pull of a giant molecular cloud.
* Gravitational Instability: As the nebula began to collapse, gravity pulled the material inward. The cloud started to rotate faster due to conservation of angular momentum.
* Heating: The gravitational potential energy converted into heat, causing the nebula to warm up.
2. Formation of the Protosun:
* Central Concentration: The majority of the nebula's mass concentrated at the center, forming a protostar.
* Nuclear Fusion: The protostar continued to grow and heat up until the core became hot and dense enough to initiate nuclear fusion, where hydrogen atoms fused to form helium, releasing vast amounts of energy. This marked the birth of the Sun.
3. Formation of the Protoplanetary Disk:
* Planetesimals: The remaining dust and gas flattened into a rotating disk around the young Sun. Gravitational forces caused particles to clump together, forming larger bodies called planetesimals.
* Accretion: These planetesimals continued to collide and merge, growing in size. This process of accretion is how the planets, moons, and other objects in the solar system formed.
4. Differentiation and Evolution:
* Planetary Differentiation: As planets grew, heavier elements like iron and nickel sank to their cores, while lighter materials like rock and ice floated to the surface. This process, called differentiation, created the layered structure of planets.
* Early Atmospheres: Some planets acquired atmospheres from the gas and dust of the protoplanetary disk or through volcanic activity.
5. Clearing of the Nebula:
* Solar Wind: The powerful solar wind from the Sun eventually swept away the remaining gas and dust, leaving behind the planets and other objects we see today.
In Summary: The collapse of the solar nebula led to a cascade of events, resulting in the formation of our Sun, the planets, and the entire solar system. This process was driven by gravity and the conservation of energy and angular momentum, and continues to shape the evolution of the solar system even today.
