Cycle of stars-science

• Nebula


  Consists of hydrogen and helium
• Nebula reaches a certain density

  Gravitational forces pull the gas together causing clumps to form
• This process takes about 1 million years, eventually forming a protostar
• As the mass and gravity of the protostar increases


  The core temperature increases
• The core temperature has to reach 15 million degrees for nuclear fusion to begin
• Nuclear fusion


  Hydrogen atoms fusing into helium atoms
• The star is powered by the nuclear fusion of hydrogen into helium
• The star will continue to burn hydrogen into helium for as long as its mass will allow
• All stars begin the same way, but the life of a star is determined by its mass
• The more massive a star, the faster its rate of fusion, and the shorter its life cycle
• Hertzsprung-Russell (HR) diagram


  • Shows the relationship between a star's temperature and its brightness
  • Most stars fall into a band called the main sequence
  • For stars on the main sequence, the hotter a star is, the brighter it is
• Star types on the HR diagram

  • Blue giants
  • Main sequence stars
  • Red supergiants
  • Red giants