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courses:phy100:9 [2023/08/12 21:42] – asadcourses:phy100:9 [2023/12/08 08:04] (current) – asad
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-====== 11. Galaxies ======+====== 9. Galaxies and Black Holes ======
  
 ===== - Galaxy types ===== ===== - Galaxy types =====
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 Look carefully toward the center of the diagram and you will notice a gap near the center where we do not see any quasar. Most inactive galaxies are actually located within that gap, meaning most of them are very close to us. Inactive galaxies are closer and more recent whereas active galaxies are distant and ancient. This immediately tells us that the ancient universe was much more violent, turbulent and chaotic than our current local universe. You need a lot of chaos and violence for getting so many active galaxies as you see around 12 billion years ago in the diagram. And this will nicely lead us to the next section where the formation and evolution of galaxies are discussed. Look carefully toward the center of the diagram and you will notice a gap near the center where we do not see any quasar. Most inactive galaxies are actually located within that gap, meaning most of them are very close to us. Inactive galaxies are closer and more recent whereas active galaxies are distant and ancient. This immediately tells us that the ancient universe was much more violent, turbulent and chaotic than our current local universe. You need a lot of chaos and violence for getting so many active galaxies as you see around 12 billion years ago in the diagram. And this will nicely lead us to the next section where the formation and evolution of galaxies are discussed.
  
-===== - Birth =====+===== - Birth in the cosmic web =====
 How did the galaxies form in the first few billion years of our history? The answer lies in the image of the universe around a million years after the big bang as shown below. During that time the universe was nothing but a homogeneous and almost isotropic conglomeration of hydrogen and helium gas. But if it was completely isotropic (the same in all directions), its picture would not look like what you see below. How did the galaxies form in the first few billion years of our history? The answer lies in the image of the universe around a million years after the big bang as shown below. During that time the universe was nothing but a homogeneous and almost isotropic conglomeration of hydrogen and helium gas. But if it was completely isotropic (the same in all directions), its picture would not look like what you see below.
  
-{{ https://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Planck_satellite_cmb.jpg/1024px-Planck_satellite_cmb.jpg }}+{{https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2013/03/planck_cmb/12583930-4-eng-GB/Planck_CMB_pillars.jpg}}
  
 You see a lot anisotropies, differences in density and temperature. Here the color indicates temperature, bluer regions are colder and denser whereas the redder ones are more hot and dilute. Pay attention to the blue dots because these tiny temperature anisotropies or overdensities gave rise to all the galaxies we know. But exactly, how? You see a lot anisotropies, differences in density and temperature. Here the color indicates temperature, bluer regions are colder and denser whereas the redder ones are more hot and dilute. Pay attention to the blue dots because these tiny temperature anisotropies or overdensities gave rise to all the galaxies we know. But exactly, how?
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 And, even more interesting, we see that an elliptical galaxy can turn into a spiral because of its interaction with a dwarf galaxy that is passing it by. The dwarf displaces some gas from the center of the elliptical and this displaced gas spirals toward the galactic center. In a few billion years this process could convert the elliptical into a spiral. And, even more interesting, we see that an elliptical galaxy can turn into a spiral because of its interaction with a dwarf galaxy that is passing it by. The dwarf displaces some gas from the center of the elliptical and this displaced gas spirals toward the galactic center. In a few billion years this process could convert the elliptical into a spiral.
 +
 +===== - Galaxy clusters and dark matter =====
 +{{https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2007/07/the_bullet_cluster2/10084622-2-eng-GB/The_Bullet_Cluster_pillars.jpg?nolink}}
  
courses/phy100/9.1691898151.txt.gz · Last modified: 2023/08/12 21:42 by asad
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