Hydrogen Burning Protonproton chain 1 H 1 H

Hydrogen Burning (Protonproton chain) 1 H + 1 H → 2 H • 2 H + 1 H → 3 He • 1 1 1 2 + 3 He → 4 He 2 2 This process is the longest stage in a star’s life!

Hydrogen Burning • The most essential nuclear fusion process in stars • The result is the formation of a Helium-4 atom • In stars with a low mass, similar to our Sun, hydrogen burning occurs through the proton-proton chain

Nuclear Fusion Step 1 Proton - Proton Fusion • • •

Nuclear Fusion Step 1 Proton - Proton Fusion • Start with 2 Hydrogen atoms • • • Hydrogen has only 1 proton

Nuclear Fusion Step 1 Proton - Proton Fusion • Start with 2 Hydrogen atoms • • Hydrogen has only 1 proton As the Hydrogen atoms fuse • 1 of the protons becomes a neutron

Nuclear Fusion Step 1 Proton - Proton Fusion • Start with 2 Hydrogen atoms • • Hydrogen has only 1 proton As the Hydrogen atoms fuse • 1 of the protons becomes a neutron • Finish with 1 Hydrogen atom • With a nucleus that has 1 proton and 1 neutron

Nuclear Fusion Step 2 Deuterium - Proton fusion • Start with Hydrogen -1 and a Hydrogen - 2 – Hydrogen -1 is 1 proton nucleus – Hydrogen -2 is 1 proton, 1 neutron nucleus •

Nuclear Fusion Step 2 Deuterium - Proton fusion • Start with Hydrogen -1 and a Hydrogen - 2 – Hydrogen -1 is 1 proton nucleus – Hydrogen -2 is 1 proton, 1 neutron nucleus • Finished with a Helium - 3 – Helium -3 is 2 protons and 1 neutron nucleus

• Start with Hydrogen -1 and a Hydrogen - 2 – Hydrogen -1 is 1 proton nucleus – Hydrogen -2 is 1 proton, 1 neutron nucleus • Finished with a Helium - 3 – Helium -3 is 2 protons and 1 neutron nucleus

Nuclear Fusion Step 3 Helium - 3 fusion

• Start with 2 Helium - 3 atoms – Helium -3 is 2 protons and 1 neutron nucleus

• Start with 2 Helium - 3 atoms – Helium -3 is 2 protons and 1 neutron nucleus • Finished with a Helium - 4 atom – Helium -4 is 2 protons and 2 neutrons – And 2 free protons

Hydrogen Burning 1 H + 1 H → 2 H • 2 H + 1 H → 3 He • 1 1 1 2 + 3 He → 4 He 2 2 This process is the longest stage in a star’s life!

Hydrogen Burning (Large Stars) • In stars much more massive than our Sun, the Hydrogen-1 and deuterium get used up very fast • Hydrogen burning occurs through the Carbon-Nitrogen-Oxygen Cycle in these stars

Hydrogen Burning (CNO Cycle)

Fusion of Heavier Elements • Once stars burn through all of their “fuel”, heavier elements begin to be fused in the core • This is how elements as heavy as iron are formed • The fusion of iron takes energy (endothermic) instead of giving off energy (exothermic). Therefore, stars begin to “die” once iron is created.

Carbon Burning 12 C 6 + + + 12 C + + + + + 12 C 6 + + + + + + → 16 O 8 + → 20 Ne 10 + ++++ + + ++ 23 Na 2 + + → 4 He + 11 + + + 4 He 2 + 2 H 1 + +

Neon Burning 20 Ne → 20 + 8 16 10 + 20 Ne 1 0 20 10 16 O + 8 + 4 He 2 4 2 + → 4 He 2 4 + 2 24 Mg 1 2 24 12 + +

Oxygen Burning 16 O + + 16 O + → + 16 O + 28 Si + 4 He + → 31 P + + + 1 H +

Silicon Burning A chain of alpha processes 28 Si + 4 He → + + 32 S + 4 He + + 28 S + → 36 Ar +

Silicon Burning (cont) 36 Si + 40 Ca + + 4 He → + + 4 He + 40 Ca + → 44 Ti +

Silicon Burning (cont) 44 Ti + 4 He + + 48 Cr + → + 4 He + 48 Cr + → 52 Fe +