The Universe & Stellar Evolution

II.   Evolution of Stars

Star types & Fate 

HR Diagram

Life Cycles
Gravity pulls together clouds of dust.  Intense pressure raises the temperature until it is hot enough for fusion to occur.

Two atoms of Hydrogen fuse to make an atom of Helium and transform some matter into huge amount of energy.

The star burns Hydrogen and gives off light.

 The HR Diagram show what kinds of stars are in the Universe.  Most stars are in- and hence astronomer think spend most  of their lifetimes in- the Main Sequence across the middle of the chart. 

 

 

 

 

 

 

 

 

 

 

 

Mass determines a star's fate:

  1. When Hydrogen fuel get used up stars swell to red giant or red supergiant.  
  2. If the star has >10 solar masses it becomes a black hole.  
  3. If the star has >1.4 solar masses it becomes a neutron star. 
  4. If the star has <1.4 solar masses it becomes a white dwarf before dying to a dark ash - a black dwarf.
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