Lecture 14
March 27, 2008
Stellar Life Cycle

Key Concepts:

  1. How are stars formed?
  2. What is the solar nebular hypothesis?
  3. What powers the luminosity of a protostar?
  4. What determines the finite range of the stellar mass?
  5. How do stars evolve during their "main sequence" phase?
  6. How do stars meet their ends?
  7. What is the ultimate fate of our Sun and the Solar System?

Sunwheel and Observatory reports due Wednesday April 1.

Stellar Birth

Astronomy Picture of the Day (2003 October 19)


Main Sequence

Low Mass Star Evolution

(watch the animation from the U. Oregon Electronic Universe Project)

Death of Stars like the Sun: Planetary Nebula

Some more examples of pretty planetary nebulae

Quiz 14C: Death of the Solar System

Evolution of a Massive (>8 solar mass) Star: Supernova

  • "Nuclear synthesis" -- formation of heavier atoms like carbon or oxygen by fusion (Carl Sagan: "we are all star stuff")
  • Fusion of heavier elements
    • electric force stronger for heavier atoms, and higher temperature is needed to overcome Coulomb barrier (100 million K to fuse helium)
    • 3 helium atoms form a carbon atom ("triple alpha process")
  • fusing heavier atoms require higher T but less energy comes out
  • core collapse: iron cannot burn and release energy, no more source of heat and pressure to counter gravity --> supernova
  • either a neutron star or a black hole is formed.


Reading assignment for next lecture: Unit 64-67