Physci

• Stellar nucleosynthesis


  The formation of elements in the center of a star
• Life cycle of stars

  1. Nebula

  2. Protostar

  3. Main sequence star

  4. Red giant

  5. White dwarf

  6. Black dwarf
• Elements formed in different stages of star cycle

  • Hydrogen and Helium (Big Bang nucleosynthesis)
  • Carbon, Oxygen, Neon, Magnesium (Helium burning reactions)
  • Elements heavier than iron (Supernova nucleosynthesis)
• How heavier elements are formed during stellar nucleosynthesis and evolution

  1. Proton-Proton Chain reaction

  2. CNO cycle

  3. Tri-alpha process

  4. Alpha ladder process

  5. Neutron capture (S-process and R-process)
• The world where we live today is just a small part of our universe
• The formation of the universe began through the Big Bang explosion 13 billion years ago
• Right after the Big Bang, protons and neutrons combined to form light elements like Hydrogen and Helium
• Other light elements like Lithium and Beryllium were also formed during Big Bang nucleosynthesis
• The other 86 elements found in nature were created in nuclear reactions in stars and in supernova explosions
• Red giant


  A dying star that has expanded and cooled down, fusing Helium into Carbon
• White dwarf


  The remnant of a red giant star, with the outer material blown off into space
• Nebula


  A giant cloud of gas and dust
• Protostar


  A star formed from a nebula due to gravity pulling Hydrogen gas together
• Main sequence star


  A star where nuclear fusion occurs at the core, converting Hydrogen into Helium
• Black dwarf


  The hypothetical remnant of a white dwarf that has cooled down and no longer emits light and heat
• Neutron star


  A star formed from a supernova explosion, the smallest known star
• Supernova


  A huge stellar explosion that releases large amounts of energy and disperses elements into space
• Black hole


  A region in space where gravity is too strong for anything to escape
• Red super giant


  A more massive main sequence star that evolves, cools, and expands faster, turning into the largest known star
• Proton-Proton Chain reaction


  The process in a main sequence star to convert Hydrogen into Helium
• CNO (Carbon, Nitrogen, Oxygen) cycle


  The process in a massive star to convert Hydrogen into Helium
• Tri-alpha process


  The process in a red giant star to convert three Helium-4 atoms into Carbon
• Alpha ladder process


  The process in a red super giant star to fuse Alpha particles and create heavier elements up to Iron
• Neutron capture


  The process where a neutron is added to a seed nucleus, forming a heavier nucleus
• 1. process (Slow process)


  Neutron capture with a slow rate, leading to radioactive decay and an increase in protons
• 1. process (Rapid process)


  Neutron capture with a faster rate, leading to the formation of heavier elements than Iron in a supernova
• Stellar nucleosynthesis


  The formation of elements in the center of a star
• Life cycle of stars

  1. Nebula

  2. Protostar

  3. Main sequence star

  4. Red giant

  5. White dwarf

  6. Black dwarf
• Heavy elements formed in different stages of star cycle

  • Carbon
  • Oxygen
  • Neon
  • Magnesium
  • Elements heavier than iron (e.g. uranium, gold)
• How heavier elements are formed during stellar nucleosynthesis and evolution

  1. Helium burning reactions (e.g. 3 helium atoms fusing to form carbon)

  2. Alpha ladder process (fusion of alpha particles to form heavier elements up to iron)

  3. Neutron capture (slow s-process, rapid r-process)

  4. Supernova nucleosynthesis (formation of elements heavier than iron)
• The world we live in today is just a small part of the universe
• The formation of the universe began through the Big Bang explosion 13 billion years ago
• Big Bang nucleosynthesis


  Formation of light elements like hydrogen, helium, lithium, beryllium
• Big Bang


  The primordial explosion that led to the formation of the universe
• The other 86 elements found in nature were created in nuclear reactions in stars and in supernovae
• Life cycle of an average star

  1. Runs out of hydrogen in core, contracts and expands into a red giant

  2. Helium fused into carbon

  3. Outer material blown off, leaving a white dwarf

  4. White dwarf cools down into a black dwarf
• Life cycle of a massive star

  1. Evolves, cools and expands into a red supergiant

  2. Carbon fusion, oxygen formed

  3. Supernova explosion, neutron star or black hole formed
• Nuclear reactions in stars

  • Proton-proton chain reaction (in main sequence stars)
  • CNO cycle (in massive stars)
  • Tri-alpha process (in red giants)
  • Alpha ladder process (in red supergiants)
• Neutron capture


  Addition of a neutron to a seed nucleus, leading to formation of heavier elements
• Types of neutron capture


  • S-process (slow, with faster radioactive decay)
  • R-process (rapid, before radioactive decay)