1. How do stars begin? Stars usually form in groups from gas clouds known as nebulæ. The process begins when the mutual gravitational attraction between all a rotating nebula's particles forces the nebula to contract. This contraction leads to acceleration of the particles and heating of the cloud. Once the contraction has proceeded far enough so that the temperature has risen to that required for nuclear fusion, the star begins to radiate solar energy. The long term stability of a star is a result of the balance between the gravitational attraction of the sun and the outward gas pressure caused by the nuclear reactions occurring at its core. |