1. Star Life Cycles

2. Stellar Nebula  Stars begin life as cloud of gas + dust  Cloud condenses and becomes more massive  Nuclear fusion begins (the power source of stars)  H + H -> He  Stars begin life as cloud of gas + dust  Cloud condenses and becomes more massive  Nuclear fusion begins (the power source of stars)  H + H -> He

3. Proto-star (Embryonic star)  Stellar Nebula continues to collapse under its own weight  star grows more massive

4. Main Sequence Star  In this stage, the outward pressure of fusion (energy) and inward pressure of gravity are balanced  Star spends more than 90% of its life  Our sun is in this stage  In this stage, the outward pressure of fusion (energy) and inward pressure of gravity are balanced  Star spends more than 90% of its life  Our sun is in this stage

5. Variable Star  Star undergoes variations in luminosity (brightness) because the forces are becoming unbalanced

6. Red Giant  As core runs out of H, nuclear fusion stops  Outer shell of star pushes outward, H gas cools and glows red  Core condenses due to gravity and He fuses into C

7. If Star is Small…  Core continues to collapse  Outer portions of star are expelled, forming a planetary nebula  Core continues to collapse  Outer portions of star are expelled, forming a planetary nebula

8. Small star, continued  As planetary nebula expands, remaining core glows white, but is much smaller than original star  White Dwarf  (Becomes black dwarf once core cools)  As planetary nebula expands, remaining core glows white, but is much smaller than original star  White Dwarf  (Becomes black dwarf once core cools)

9. Supernova  Star runs out of fuel, and force of gravity starts to condense remaining material  Incredible inward force restarts nuclear fusion, causing an incredible explosion  Star runs out of fuel, and force of gravity starts to condense remaining material  Incredible inward force restarts nuclear fusion, causing an incredible explosion

10. Supernova Remnant  After explosion, an ever-expanding shock wave spreads out.  Cloud of debris and other stellar material is seen expanding from explosion

11. Black Hole…  After explosion, star material can become so dense that all material, even light, can collapse into an infinitely small space

12. …or, a Neutron Star  If not as much mass remains, the left- over material can re-condense and become a star again  Much smaller and less bright than parent star

13. The Cycle

14. Another View of the Cycle

15. Annndd…..yet one more