8.1.3 Fusion in Stars

• What is the fundamental process that powers stars, including our Sun?

  Fusion
• What is nuclear fusion?

  Nuclear fusion is a process where atomic nuclei combine to form a heavier nucleus, releasing energy.
• What happens when light nuclei collide with sufficient force during fusion?

  They overcome their electrostatic repulsion and fuse to form a heavier nucleus.
• Where does fusion occur in stars?

  In the cores of stars.
• What are the core conditions necessary for fusion in stars?

  Extremely high temperature, pressure, and density.
• What is the primary fusion reaction in the cores of most stars?

  Hydrogen nuclei fuse to form helium.
• What are the stages of the proton-proton chain reaction?

  1. Two protons fuse to form deuterium, a positron, and a neutrino.

  2. Deuterium fuses with another proton to form helium-3 and release a gamma ray.

  3. Two helium-3 nuclei fuse to form helium-4 and release two protons.
• How is energy released during fusion reactions?

  The mass of the final helium nucleus is less than the total mass of the original hydrogen nuclei, and this mass difference is converted into energy.
• What is the CNO cycle in stars?

  It is a fusion process where carbon, nitrogen, and oxygen act as catalysts to convert hydrogen into helium in more massive stars.
• What are the steps of the CNO cycle?

  1. Carbon-12 captures a proton to form nitrogen-13.

  2. Nitrogen-13 undergoes beta decay to form carbon-13.

  3. Carbon-13 captures another proton to form nitrogen-14.

  4. Nitrogen-14 captures another proton to form oxygen-15.

  5. Oxygen-15 undergoes beta decay to form nitrogen-15.

  6. Nitrogen-15 fuses with a proton to form helium-4 and carbon-12, repeating the cycle.
• What happens to stars when hydrogen in the core is exhausted?

  The core contracts and heats up, causing the outer layers to expand and cool.
• What are red giants and supergiants?

  They are stars that have exhausted hydrogen in their cores and have started helium fusion.
• How are heavy elements formed in stars?

  Heavy elements are formed during supernova explosions and through fusion processes in massive stars.
• What are white dwarfs?

  They are remnants of low-to-medium mass stars where fusion has ceased, leaving a dense, cooling core.
• What forms from the remnants of massive stars after supernova explosions?

  Neutron stars and black holes.
• What is the role of solar fusion in the Sun?

  Solar fusion in the Sun's core converts hydrogen nuclei into helium, releasing energy that radiates outward as sunlight.
• What supports the Sun against gravitational collapse?

  The energy released from fusion reactions in the Sun's core.
• What are the current challenges in fusion research?

  • Achieving and maintaining extreme conditions for fusion on Earth.
  • Ensuring energy output exceeds energy input for sustainability.
• What is the purpose of fusion reactors being researched by scientists?

  To create a clean and virtually limitless energy source.
• What is ITER?

  ITER is an international project aiming to demonstrate the feasibility of fusion power.
• What are the key points about nuclear fusion in stars?

  • Fusion combines lighter atomic nuclei to form heavier nuclei, releasing energy.
  • Occurs in the core, primarily converting hydrogen into helium.
  • Includes the proton-proton chain and CNO cycle.
  • Drives the life cycle of stars and the formation of heavier elements.
  • Scientists are exploring controlled fusion for sustainable energy production.