1. Gravitational Collapse: The nebula was pulled together by its own gravity, causing it to shrink. As the cloud collapsed, the particles within it collided, generating heat.
2. Protostar Formation: Eventually, the center of the collapsing cloud became so hot and dense that it formed a protostar. This protostar continued to grow as it attracted more material from the surrounding nebula.
3. Nuclear Fusion Ignition: At the core of the protostar, the temperature and pressure became so extreme that nuclear fusion ignited. This is the process where hydrogen atoms fuse together to form helium, releasing immense amounts of energy. This energy is what powers the Sun and gives it its light and heat.
4. Main Sequence Star: Once nuclear fusion began, the protostar became a main sequence star, which is what the Sun is today. The Sun is currently in the middle of its main sequence lifetime, where it will continue to burn hydrogen for billions of years.
So, in short, the Sun formed from a giant cloud of gas and dust that collapsed under its own gravity, igniting nuclear fusion in its core and becoming a star.
