Here is simple illustration of stars life cycle
Now, lets discuss every stage:
Before I start to
explain all stars' life cycles, I have to give credit to Fred Hoyle. From his
ideas and theories, I get my explanation of the cycles.
As space expands there are many more gaps forming and they need to be filled by stars and energy. So stars need to have a dynamic life cycle. Moments of birth and death, right?
Stars form when hydrogen atoms in space are pulled together in bigger and bigger spheres. As the atoms are crushed together they start to fuse and form helium (the next heaviest element). That process of atomic fusion involves huge amounts of energy! The reactions on the sun are like atomic bomb going off on Earth. Except the atomic bomb would be like a balloon popping compared to the entire Earth exploding. The release of this energy does two things.
A lot of it provides an outward explosive pressure to counterbalance the inward pressure of gravity in the emerging star. This allows the star to remain stable for billions of years. Despite all the reactions going on the stat doesn't explode nor implode.
Secondly, the other energy is released as heat or light. Hoyle's theory explained why stars shine. The hydrogen eventually starts to run out leaving the predominate chemical as helium. With less hydrogen to fuel the fusion reactions there will be less outward pressure, and the balance will be interrupted. As the pressure builds up the inward gravitational forces will increase and become powerful enough to press all the newly created helium atoms tighter and tighter. They will start to fuse forming the next heaviest elements. This process will continue. When all the elements up to iron have been produced by fusion, it would take tremendous heat to produce the next heaviest elements.
Smaller stars can't provide that heat. They begin to die. All the other lighter elements are shed into space and it starts to cool down. It leaves a hot iron core known as a white dwarf, then a brown dwarf, and then a cold iron core waiting it's fate of being annexed by larger objects or just remaining static.
Larger stars, though they can produced elements heavier than iron, have so much inward gravitational force, they began to crush the iron core until it implodes. As the star dies in a dramatic explosion (supernova) a great cloud of hot shining brown dust is thrown into space and astronomer's have seen it!
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