Today we discussed X-rays in more detail. Here are the notes that I took.
Vikram Dwarkadas
What are X-rays 
-Highly energetic form of light, not visible to human eyes
-Emitted by objects at temperatures&gt;1 million degrees
Energetic phenomena temperatures of million degrees(very large gravitational potentials:BH, clusters of galaxies)
Wein's law
Looking for the source of X-rays 
X-rays are absorbed more by bone than skin, so the bone seems lighter 
Intervening objects (like gas, interstellar medium, etc.) may absorb some of the X-rays 
Low energy photons combined with high energy electrons can make X-rays 
(Charge exchange)
Gas origin:
-Mass ejected by old stars 
-Gas falling back on the galaxy 
Gas heating mechanism:
-Shock heating
-Supernovae 
-AGN feedback?
Bremsstrahlung (braking radiation) 
X-rays do not reflect off mirrors like optical light 
Absorption 
X-rays absorbed by the atmosphere:
-X-ray astronomy only began in 1960s
-Can only observe using balloons, satellites


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