The Life Cycle Of A Star

• Stars initialy form from clouds of dust and gas.
• The force of gravity makes them spiral together to form a protostar.
• Gravitational energy is converted into heat energy - temperature rises.
• When the temperature gets high enough hydrogen nuclei undergo nuclear fusion to form helium nuclei and give out massive amounts of heat and light.    A star is born. 
• Smaller masses of gas and dust may pull together to make planets that orbit the star. The star immediately enters a long stable period.
•  The heat created by the nuclear fusion provides an outward pressure which balances the inward force of gravity.
• The star maintains its energy output for millions of years due to massive amounts of hydrogen it consumes.
• In its stable period it is called a main sequence star.  This lasts for several(10) billion years
• Eventually hydrogen begins to run out. Heavier elements like iron are made by by nuclear fusion of helium. Small stars become a Red Giant and big stars become Red Super Giant if big. It becomes red because the surface cools.

Red giant

• A small star like our sun will then begin to cool and contract into a white dwarf.
• As light fades completely it becomes a black dwarf.

Super Red Giants

• Big stars however start to glow brighty again and undergo more fusion and expand and contract forming elements as heavy as iron.
• Eventually they expload in a supernova.
• This throws our layers of dust and gas into space leaving a very dense core called a neautron star.
• If the star is big enough it will become a black hole.
• The dust and gas thrown off by the Supernova will form a Second Generation Star

The heavier elements are only made in the final stages of a big star just before the final supernova. The presence of heavier elements in the Sun and inner planets is clear evidence our world was formed this way.