A star is formed out of cloud of cool, dense molecular gas that collapses and increases in density. This can happen when the cloud collides with another dense molecular cloud or it is near enough to another cloud to encounter the pressure caused by a giant supernova. Multiple stars can be formed at once with the collision of two galaxies. In both instances, heat from the mutual gravity pulling all the material inward is required in order to fuel the reaction. The newborn star is called a protostar.
Next, the protostar can become a brown dwarf (a sub-stellar object that cannot maintain high enough temperatures to perpetuate hydrogen fusion to helium) if it's a small star. If it's a medium or large protostar, it can either undergo a proton-proton chain reaction to convert hydrogen to helium, or a carbon-nitrogen-oxygen cycle to convert hydrogen to helium. The difference is that the carbon-nitrogen-oxygen cycle occurs at much higher temperatures. After any of these processes, a new star is formed.
From there, the life cycle depends on how quickly the star consumes hydrogen. Once it has consumed most of its hydrogen, it is considered to be mature.
No comments:
Post a Comment