Download Lecture Notes on the Sun: Structure, Interior, and Thermonuclear Reactions in Astronomy II and more Study notes Astronomy in PDF only on Docsity! ASTR-1020: Astronomy II Course Lecture Notes Section II Dr. Donald G. Luttermoser East Tennessee State University Edition 4.0 Abstract These class notes are designed for use of the instructor and students of the course ASTR-1020: Astronomy II at East Tennessee State University. Donald G. Luttermoser, ETSU II–3 takes approximately 1 million years for these photons to escape the solar interior. 3. Heat energy can be transported by one of 3 mechanisms: a) Radiation transport: Photon flow (e.g., sunlight). b) Convection: Blobs of hot gas rise from hotter regions to cooler regions (e.g., boiling water). c) Conduction: Atom and molecule collisions in a mate- rial (e.g., an iron rod in a fire). 4. The energy transport mechanism that nature will use in a given situation is the one that is most efficient in transporting the energy. 5. In the Sun’s interior, the core and much of its interior is radiative =⇒ energy flows via photons =⇒ radiative zone. 6. Convection is the most efficient means of energy transport in the outer layers of the interior =⇒ convection zone. We see the top of this zone in the photosphere as granulation (as discussed in Astronomy I). II–4 ASTR-1020: Astronomy II Core (radiative, with nuclear reactions)Radiative Zone Convective Zone Solar Interior 1 Rsun 0.3 Rsun 0.75 Rsun C. Thermonuclear Reactions 1. The Sun’s energy is produced by thermonuclear reactions in the core of the Sun. a) Temperatures are high enough for 4 hydrogen (H) atoms to fuse into 1 helium (He) atom continuously at a very high rate. b) The mass difference between 4 H atoms and 1 He atom is converted into energy via Einstein’s famous equation E = mc2, where E is the energy liberated, m is the mass difference, and c is the speed of light: 4 H atoms mass = 6.693 × 10−27 kg – 1 He atom mass = −6.645 × 10−27 kg Mass Difference = 0.048 × 10−27 kg c) The Sun produces 9.0×1037 of these reactions per second releasing 3.9 × 1026 Joules of energy per second. Donald G. Luttermoser, ETSU II–5 2. There are two different reaction chains that occur when hy- drogen is being fused into helium: the proton-proton chain, which occurs in low mass stars like the Sun, and the carbon- nitrogen-oxygen (CNO) cycle, which occurs in high mass stars. a) The proton-proton chain is as follows: 1H + 1H −→ 2H + e+ + ν (occurs twice) 1H + 2H −→ 3He + γ (occurs twice) 3He + 3He −→ 4He + 1H + 1H (for each time this occurs) i) 1H = hydrogen atom (1 proton). ii) 2H = heavy hydrogen (1 proton + 1 neutron) = deuterium. iii) 3He = light helium (2 protons + 1 neutron). iv) 4He = helium (2 protons + 2 neutron) = alpha particle (normal helium). v) γ = gamma ray photon. vi) e+ = positron (positive charge) = anti-electron (antimatter). vii) ν = neutrino (neutral particle). b) The CNO cycle: 12C + 1H −→ 13N + γ 13N −→ 13C + e+ + ν 13C + 1H −→ 14N + γ 14N + 1H −→ 15O + γ 15O −→ 15N + e+ + ν 15N + 1H −→ 12C + 4He
