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UA - PH/AY 101 - Class Notes - Week 12

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UA - PH/AY 101 - Class Notes - Week 12

School: University of Alabama - Tuscaloosa
Department: Astronomy
Course: AY 101 - Intro to Astronomy - Jeremy Bailin
Professor: Jeremy Bailin
Term: Spring 2015
Tags:
Name: AY 101 - Nov 15 Lecture Notes
Description: Lecture Notes from Tuesday, November 15th
Uploaded: 11/15/2016
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background image AY 101 – NOV 15  Galactic Recycling    Heavy elements form inside stars, get injected into interstellar gas, where they form into new  stars    Discuss: which had a higher a fraction of heavy elements—stars that formed early in the galaxy  or more recently?  o  later    Consider: what impact might that have on whether those stars have parents?  The Mass of the Milky Way    Enclosed Mass – how much mass is there in total inside of that ‘point’?  o  Enclosed Mass Diagram  Dark Matter    There is about 10x more matter in the milky way than we can account for by adding up  everything we see    Also true of other galaxies (Rubin) and clusters of galaxies (Zwicky) 
  It has mass—that is how we know it’s there 
  It does not interact with light.. it doesn’t emit or absorb it (invisible matter would be a better 
name)    Dark matter is an extended halo that dominates beyond 30,000 light years   
What is it? 
  Things that have been ruled out:  o  Faint white dwarfs 
o  Faint brown dwarfs 
o  Free-floating planets 
o  Cold molecular gas 
o  Miniature black holes 
o  Neutrinos 
o  Anything made out of normal matter (protons, electrons, neutrons) 
  Must be some type of new particle that we haven’t been able to detect yet  Dark Matter v. Modified Gravity    Scientific Theory: gravity 
  Model: motions caused by gravitational forces from the visible mass 
  Observations: motions are too fast 
Other Galaxies    3 major types  1.  “Spiral” or “Disc” Galaxies    Examples: Milky Way, Andromeda  
background image   Mainly disk, plus some center bulge 
  Spiral arms in the disc 
  Some have “bars” in the middle 
  Contain stars, gas, dust, and active star formation 
2.  “Elliptical” or “Spheroidal” Galaxies    Example: M87 
  Entirely bulge 
  Only old stars plus some very hot gas 
  Most massive galaxies are all ellipticals 
3.  “Irregular” Galaxies    Example: Large Magellanic Cloud 
  Don’t have a symmetrical pattern 
  Some are interacting galaxies, some are low-mass irregular discs 
The Galactic Center    4 million Mass of Sun 
  Smaller than the solar system 
  Doesn’t shine 
  What is it? 
1.  Black Hole    Milky Way mass: 10^12 MSun 
  Milky Way’s black hole mass: 4x10^6 MSun 
  Almost 1 million times smaller  Quasars and Active Galactic Nuclei    All galaxies have a supermassive black hole at their center 
  Unlike the Milky Way, some of them have a lot of gas falling into the black hole in an accretion 
disk    Seen as:  o  Optical jet 
o  Radio jets/lobes 
o  Optical/X-ray bright points at the centers of galaxies 
  Nucleus can be 1000x brighter than the rest of the galaxy 
  Quasars: active galaxies that are so far away, and whose nucleus is so much brighter that all you 
can see is the nucleus  o  Not until Hubble Space Telescope were the host galaxies of quasars directly seen 
o  Gas in a hot accretion disk around a supermassive black hole at the center of a galaxy 
that outshines the entire galaxy  Star Formation Rates    How fast is a galaxy currently turning gas into stars? 
  Some ways of measuring: 
o  Counting young stars 

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School: University of Alabama - Tuscaloosa
Department: Astronomy
Course: AY 101 - Intro to Astronomy - Jeremy Bailin
Professor: Jeremy Bailin
Term: Spring 2015
Tags:
Name: AY 101 - Nov 15 Lecture Notes
Description: Lecture Notes from Tuesday, November 15th
Uploaded: 11/15/2016
3 Pages 12 Views 9 Unlocks
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  • 24/7 Homework help
  • Notes, Study Guides, Flashcards + More!
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