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Home , Stellar nucleosynthesis

Lesson 4: Stellar Explosions and

Reading Assignment

• Chapter 21.2: The End of a High-Mass • Chapter 21.1: after Death for White Dwarfs • Chapter 21.3: Supernovae • Discovery 21-1: 1987A • Chapter 21.4: The Formation of the Elements • Chapter 21.5: The Cycle of Stellar • Chapter 22.1: Neutron Stars • Chapter 22.2: • Chapter 22.3: Neutron-Star Binaries

Summary of Stellar

• Read Chapter 20.2, Chapter 20.3, and Chapter 21.4. • : 1H • neutron: n • (2 + 2 ): 4He • beryllium-8 (4 protons + 4 neutrons): 8Be • -12 (6 protons + 6 neutrons): 12 C • -16 (8 protons + 8 neutrons): 16 O • -20 (10 protons + 10 neutrons): 20 Ne • magnesium-24 (12 protons + 12 neutrons): 24 Mg • -28 (14 protons + 14 neutrons): 28 Si • sulfer-32 (16 protons + 16 neutrons): 32 S • -36 (18 protons + 18 neutrons): 36 Ar • calcium-40 (20 protons + 20 neutrons): 40 Ca • titanium-44 (22 protons + 22 neutrons): 44 Ti • chromium-48 (24 protons + 24 neutrons): 48 Cr • -52 (26 protons + 26 neutrons): 52 Fe • iron-56 (26 protons + 30 neutrons): 56 Fe • iron-57 (26 protons + 31 neutrons): 57 Fe • iron-58 (26 protons + 32 neutrons): 58 Fe • iron-59 (26 protons + 33 neutrons): 59 Fe • cobalt-56 (27 protons + 29 neutrons): 56 Co • cobalt-59 (27 protons + 32 neutrons): 59 Co • cobalt-60 (27 protons + 33 neutrons): 60 Co • nickel-56 (28 protons + 28 neutrons): 56 Ni • nickel-60 (28 protons + 32 neutrons): 60 Ni • : e - • positron (antimatter electron): e + • electron : νe • antimatter electron neutrino: < νe> • photon (): γ • Hydogen burning • Proton-proton chain reaction: 1 4 1 + • 6( H) → He + 2( H) + 2e + 2 νννe + 2 γγγ • CNO cycle: 12 1 12 4 + • C + 4( H) → C + He + 2e + 2 νννe + 3 γγγ • For a 20-solar mass star, this continues for about 10 million years. • Carbon formation • Triple-alpha reaction: • 1. 4He + 4He → 8Be + γγγ • 2. 8Be + 4He → 12 C + γγγ • So ovarall: • 3( 4He) → 12 C + 2 γγγ • For a 20-solar mass star, this continues for about 1 million years. • You are carbon based – this is where you come from! • Carbon burning • Major reaction: 12 C + 4He → 16 O + γ • Minor reaction: 12 C + 12 C → 24 Mg + γ • For a 20-solar mass star, this continues for about 1 thousand years. • This is where the oxygen that you breathe comes from. • Oxygen burning • Major reaction: 16 O + 4He → 20 Ne + γγγ • Minor reaction: 16 O + 16 O → 32 S + γ • For a 20-solar mass star, this continues for about 1 year. • This is where the neon in neon signs comes from – Viva Las Vegas! • Helium capture • The triple-alpha reaction and the major carbon and oxygen burning reactions are helium capture reactions. The capture of helium nuclei continues until silicon is created, at which point the supply of helium nuclei in the star’s core is depleted: • 20 Ne + 4He → 24 Mg + γγγ • 24 Mg + 4He → 28 Si + γγγ • For a 20-solar mass star, this continues for about 1 month. • This is where the primary ingredient for silicone comes from. • Iron formation • : • Fortunately, by the time that silicon is created the star’s core has grown hot enough to make blackbody photons of high-enough energy to break up some of the silicon. This is called : • 28 Si + γγγ → 7( 4He) • Consequently, helium capture can again proceed: • 28 Si + 4He → 32 S + γγγ • 32 S + 4He → 36 Ar + γγγ • 36 Ar + 4He → 40 Ca + γγγ • 40 Ca + 4He → 44 Ti + γγγ • 44 Ti + 4He → 48 Cr + γγγ • 48 Cr + 4He → 52 Fe + γγγ • 52 Fe + 4He → 56 Ni + γγγ • For a 20-solar mass star, this continues for about 1 week. • This is where the primary ingredients for gun powder, your bones, Lieutenant Dan’s magic legs, chrome plating, etc., come from. • : • 56 Ni has too many protons to be stable and radioactively decays: 56 56 + • Ni → Co + e + νννe + γγγ • 56 Co has too many protons to be stable and radioactively decays: 56 56 + • Co → Fe + e + νννe + γγγ • For a 20-solar mass star, this continues for about 1 day. • This is where the primary ingredient for steel comes from. • Heavy element formation • Slow (s-process): • 56 Fe + n → 57 Fe • 57 Fe + n → 58 Fe • 58 Fe + n → 59 Fe • 59 Fe has too many neutrons to be stable and radioactively decays: 59 59 - • Fe → Co + e + < νννe> + γγγ • 60 Co + n → 61 Co • 61 Co has too many neutrons to be stable and radioactively decays: 61 61 - • Co → Ni + e + < νννe> + γγγ • This continues, making the rest of the elements through bismuth-209 (83 protons + 126 neutrons), including such famous elements as copper, silver, lead, gold, etc. • Rapid neutron capture (r-process): • To make elements heavier than bismuth-209, neutron capture must proceed more rapidly than it takes for the newly formed elements to radioactively decay back to where they started. This is possible only for about 15 minutes, during the supernova explosion itself. This is how such famous radioactive elements as uranium and plutonium are produced.

Homework 4

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