Star Formation

• What is required for nuclear fusion to occur?

  High kinetic energy to overcome repulsion
• What are the conditions required for nuclear fusion?

  Very high temperature, pressure, and density
• How many hydrogen nuclei are fused to form one helium nucleus?

  Four hydrogen nuclei
• What particles are produced during the fusion of hydrogen into helium?

  Two gamma-ray photons, two neutrinos, two positrons

  
• What is the result of nuclear fusion in terms of energy?

  Massive amounts of energy are released
• What is radiation pressure in stars?

  Outward acting pressure from gamma-ray photons
• What initiates the fusion of hydrogen nuclei in a star?

  Core temperature reaching millions of degrees Kelvin
• What happens to a protostar's gravitational field as it attracts more gas and dust?

  It increases the temperature and pressure of the core
• How does the kinetic energy of particles change as fusion occurs?

  Kinetic energy increases with more frequent collisions
• What occurs when fusion reactions begin in a star's core?

  They produce outward radiation pressure
• What is equilibrium in stars?

  Balance between inward gravitational force and outward radiation pressure
• What happens to gas pressure as a star's temperature increases?

  Gas pressure increases due to gravitational collapse
• What forces act outward to balance gravitational force in a star?

  Gas pressure and radiation pressure
• What happens if the temperature of a star increases?

  Outward pressure will also increase
• What occurs if outward pressure exceeds gravitational force?

  The star will expand
• What happens if the temperature of a star drops?

  Outward pressure will also decrease
• What occurs if outward pressure is less than gravitational force?

  The star will contract
• What is necessary for a star to remain stable?

  Outward and inward forces must be balanced