Sections Review

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black hole event horizon giant molecular cloud
helium flash main sequence neutron star
planetary nebula protostar red giant
shell burning stellar nucleosynthesis subgiant
supergiant supernova T-Tauri
white dwarf


  1. Star main sequence lifetime = [star's mass / star's luminosity] × 1010 years.
  2. Star main sequence lifetime = 1010 / (star's mass)(p - 1), where p = 3 for stars more massive than 30 solar masses and p = 4 for stars less massive than 10 solar masses.

Review Questions

  1. What fundamental property of stars determines their evolution?
  2. Why do massive stars last for a short time as main sequence stars but low-mass stars last a long time in the main sequence stage?
  3. How can you detect protostars if the surrounding gas and dust blocks visible light?
  4. How do T-Tauri stars get rid of the surrounding gas and dust from which they formed?
  5. What is happening in the core of a main sequence star and why is it so stable?
  6. What happens to a main sequence star that has stopped fusing hydrogen in its core?
  7. Are all red giants or supergiants very massive stars? Why are red giants so big and red? What is going on inside the giants?
  8. What is the evolution sequence for stars around the mass of our Sun? How long is the Sun's main sequence lifetime?
  9. What will happen to a hot, blue star (> 10 solar masses) during its entire lifetime?
  10. What will happen to a cool, red star (< 0.5 solar masses) during its entire lifetime?
  11. In which stage is most of a star's mass lost?
  12. How is a planetary nebula formed? What is formed at the center of the planetary nebula? Which main sequence stars will eventually form planetary nebulae?
  13. What happens in a supernova explosion? Which main sequence stars will eventually go supernova?
  14. How can you distinguish planetary nebulae and supernovae from each other and from ordinary H II regions?
  15. About how often does a supernova occur in a typical galaxy? Why is it better to look for supernovae in other galaxies?
  16. How does the concept of stellar nucleosynthesis explain where all of the elements on the Earth came from?
  17. Why is iron the limit for stellar nucleosynthesis in red giants? Where did heavier elements than iron come from?

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last updated: 25 May 2001

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Author of original content: Nick Strobel