Lesson 2

• Isotope


  Species of an atom of the same element with the same number of protons but different number of neutrons
• Arthur Eddington proposed in the 1920s that atoms of light elements fuse together within stars to form heavier atoms
• Hydrogen Fusion


  Nuclear fusion of four protons to form a helium-4 nucleus, dominant reaction in main sequence stars' cores
• Horizontal branch stars


  • Use helium as fuel
• Photons emitted through decoupling during the Recombination period comprise the cosmic microwave background (CMB)
• Most abundant elements in the universe

  • Hydrogen
  • Helium
• Photon decoupling


  Interaction of electrons and photons decreases as electrons become bound to nuclei, emitting photons
• The energy lost in the chain reaction through neutrino and gamma ray emission fuels the stars
• Triple Alpha Process

  Formation of Carbon from three Helium-4 (alpha particles) through Beryllium-8
• Atomic number


  Corresponds to the number of protons in an atom
• Stars are formed after 150 million years as gravity causes gases and dust to collapse
• Alpha Ladder is a series of nuclear fusion by adding alpha particles
• Big Bang Nucleosynthesis


  Production of light elements during the expansion of the universe, including Hydrogen, Helium, Lithium, and Beryllium
• Recombination happens when charged electrons and protons become bound to form electrically neutral atoms
• Light is also called electromagnetic (EM) radiation. An example of EM radiation is microwave radiation
• Stellar Nucleosynthesis


  Formation of elements through nuclear fusion inside stars
• Atoms


  Building blocks of matter, composed of subatomic particles, differ in the number of protons in their nucleus
• Main Sequence Stars

  • Use hydrogen as fuel (e.g., Sun, Sirius, Alpha Centauri A and B)
• Nucleosynthesis


  Formation of elements by creating new atomic nuclei from pre-existing nucleons and nuclei
• Other heavier elements like carbon, nitrogen, and oxygen are formed by nuclear fusion
• Hydrogen Fusion


  The energy lost in the chain reaction through neutrino and gamma ray emission fuels the stars
• CNO Process (Carbon-Nitrogen-Oxygen Process)


  The 'CNO cycle' refers to the Carbon-Nitrogen-Oxygen cycle, a process of stellar nucleosynthesis in which stars on the Main Sequence fuse hydrogen into helium via a six-stage sequence of reactions. A carbon-12 nucleus captures a proton and emits a gamma ray, producing nitrogen-13
• Alpha Ladder


  • Carbon + Helium = Oxygen
  • Oxygen + Helium = Neon
  • Neon + Helium = Magnesium
  • Magnesium + Helium = Silicon
  • Silicon + Helium = Sulfur
  • Sulfur + Helium = Argon
  • Argon + Helium = Calcium
  • Calcium + Helium = Titanium
  • Titanium + Helium = Chromium
  • Chromium + Helium = Iron
• Neutron Capture


  The rapid neutron-capture process, also known as the r-process, is responsible for the creation of approximately half of the atomic nuclei heavier than iron
• Triple Alpha Process

  The formation of Carbon from three Helium-4 (alpha particles) through Beryllium-8
• When the star reaches iron, stellar nucleosynthesis comes to a halt because the nucleus of iron is tightly bound
• Types of Supernova Nucleosynthesis

  • Neutron
  • Slow Neutron Capture
  • Rapid Neutron Capture
  • Proton Capture
• Supernova is a powerful stellar explosion marking a star’s end of its evolutionary stage
• After 150 years, stars are formed as gravity causes gases and dusts to collapse
• Isotope


  An Isotope is a species of an atom of the same element with the same number of protons but different number of neutrons
• Essential elements to life formation

  • Carbon
  • Nitrogen
  • Oxygen
• Supernova Nucleosynthesis


  When a star runs out of nuclear fuel and can no longer undergo fusion reactions, gravity causes the star to collapse. The explosion of the star momentarily generates high enough temperatures and pressures to cause nuclear fusion reactions that make elements with atomic numbers 27-92 (Cobalt to Uranium)
• Since only the largest stars can explode in supernovae events, elements with atomic numbers 27-92 are rarer than elements with atomic numbers 1-26
• Alpha Ladder


  A series of nuclear fusion by adding alpha particles to form heavier nuclei
• Once a star runs out of fuel, it collapses and explodes