Stars

Key Points
Hydrostatic Equilibrium

Photons through radiative diffusion release energy

Nuclear Fusion: 4 Hydrogen-> 1 Helium, small change of atomic mass converted to energy

Collapsing increases heat and burns fuel faster

High mass stars burn quickly, short lived, bigger radius, bluer, and hotter
Low mass stars live long, are dim, redder, and colloer

A star’s life:

• Main Sequence on HR Diagram: Indicates Hydrogen burning in the core.
  
• Stars leave main sequence as they begin to burn heavier elements
  
• Red Giants are brighter because they swell and increase in surface area
  
• Chandrasekhar Mass ~ 1.4 solar masses is upper limit to white dwarf mass because electron degeneracy pressure breaks down there and star would become black hole. If this happens as a star accretes mass from a binary companion, you get a Type I Supernova. The result is probably a black hole.
  
• If star fuses all the elements and has created a Iron core, the collapse of stuff around the core bounces and creates a Type II Supernova. The result is often a neutron star.
  
  

1. What affects the properties (mass, pressure, rate of fusion) of a star? How so?
   
2. What are the properties of a black hole versus a white dwarf?
   
3. What does a spectra tell you about a star?
   
4. Draw a main sequence on an HR diagram. Be sure to label the axes.
   
   1. Why do stars leave the main sequences?
      
   2. Where do they go?
      
   3. What are they called?
      
5. Compare and contrast low and high mass stars.
   
6. What elements are low mass and high mass stars able to fuse for energy?
   
7. Why are red giants giant?
   
8. Why are white dwarves dwarfs?
   
9. How do black holes form?
   
10. Why do black holes emit x-rays?
    
11. Explain the redshift of light as it leaves a black hole.
    
12. How does energy get from the inside to the outside of a star?
    
13. What are the 3 ways that energy can be transferred?
    
    1. Which two apply to stars?