life cycle of a star

life cycle of a star

1. Formation

   • when enough dust and gas clump together
     • gravitational forces
     • nuclear reactions produce energy to keep the star hot
   • planets formed when smaller amounts of dust and gas clump
   • gravity pulls gas and dust together
   • As the gas falls together, it gets hot. A star forms when it is hot enough for nuclear reactions to start. This releases energy, and keeps the star hot.

2. some stable stars change in their lifetime to form other types of stars

   • E.g sun is a stable star
   • forms many different types
     • red giant
     • white dwarf
     • neutron stars
     • black holes

3. during a stars main sequence period of life it is stable

   • forces are balanced
     • outward pressure from expanding hot gases is balanced by the force of the stars gravity
   • our sun is currently in its stable phase

4. stages of lifecycle determined by size

   • life cycle of a star:
   • stars the same size as our sun
     • follow the left hand path
       • main sequence> red giant>white dwarf> black dwarf
   • stars much bigger than our sun
     • follow the right hand path
       • main sequence>super red giant>supernova>neutron star or blackhole

5. nuclear fusion in a star

   • stars are so hot nuclear fusion can take place
     • stars have enough hydrogen to maintain energy output for millions of years
   • used in order to release energy
   • hydrogen nuclei fuse together to form helium nuclei
     • as the star runs out of hydrogen other fusion reactions take place and start to form other element nuclei
       • heavier elements than hydrogen (<Fe) are formed
         • elements >Fe are formed in supernovas
           • heavy elements are found in the sun and planets, suggesting that they were formed from the remains of earlier stars that exploded as supernovas

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