How Stars are Formed

Stars form through a complex process that begins with the fragmentation and contraction of large molecular clouds. These clouds are composed primarily of hydrogen and helium gas, along with traces of heavier elements and dust particles. As a cloud contracts under its own gravity, it breaks apart into smaller fragments due to increasing gravitational forces within the denser regions of the cloud. Each of these fragments may go on to form a star.

As a cloud fragment continues to contract, the molecules and dust particles become more tightly packed, making it harder for infrared and radio photons to escape. This trapping of thermal energy causes the internal pressure and temperature to increase, slowing down the contraction. The center of the cloud fragment becomes a protostar at this stage, although nuclear fusion has not yet begun. Matter from the surrounding cloud continues to fall onto the protostar, causing it to grow until either the protostar itself or a neighboring star blows away the remaining gas.

The rotation of the contracting cloud plays a crucial role in the formation process. As the cloud contracts, its rotation speed increases, causing the cloud to flatten into a disk. This rotation also leads to the formation of jets of matter that shoot out along the rotation axis, which can ram into interstellar gas and cause it to glow. The protostar continues to contract until its core becomes hot enough for nuclear fusion to begin. Once the energy released by core fusion balances the energy radiated from the surface, the protostar becomes a main-sequence star.