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GenGeoAstroII Cosmology

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GenGeoAstroII Cosmology Powered By Docstoc
					Other galaxies

   Stars rarely collide…

   But galaxies do…




                 (observations !)
Other Galaxies

   galaxy mergers




    (computer simulation !)
Other galaxies

   Do other galaxies also contain supermassive
    black holes ?            YES !




Similar to accretion
disk-jet connection in
young stellar objects
 Going to larger scales:
•Many galaxies are in clusters (“group”= small cluster)
• Local group:
           - small cluster containing the milky way
            - about 20 galaxies within a cubic parsec
            - 3 spirals: Milky Way, Andromeda (“M31”),
                         M33
            - 4 irregulars: MW-satellites Small and Large
                            Magellanic Clouds
            - several dwarf ellipticals

•Virgo Cluster: - nearest rich cluster
                 - about 2500 galaxies
                 - distance about 15 Mpc
Virgo Cluster
Midterm exam:
  astrophysics
• date: May 11, 2005, 8:15 a.m.
• location: Conrad Naber Hall
• bring pocket calculator
• NO text books, notes laptops etc.
• do NOT bring your own paper
• write on exam sheets directly

 Spacephysics: see web site
Cosmology

        Mythology and Modern
 Ancient
 Cosmology:

 Is there a/Where is the difference ?
Example of a creation Story:
The Christian/Jewish View

 Genesis: In the beginning God created the heavens
 and the earth. And the earth was waste and void;
 and darkness was upon the face of the deep …
Common Concepts:

 Action of a supreme craftsman
 Generation from a seedling/egg
 Imposition of order over “chaos”
 Life cycle dominates over
  eternal/unchanging: there is a beginning
 Hybrid schemes: act of creation, but
  supreme being/chaos existed forever
Scientific “Creation” Story 2005:
 In the beginning there was neither space nor time
 as we know them, but a shifting foam of strings
 and loops, as small as anything can be. Within the
 foam, all of space, time and energy mingled in a
 grand unification. But the foam expanded and
 cooled. And then there was gravity, and space and
 time, and a universe formed. …


 Is there a difference ?
   The Scientific Method
                      general principle



              induction            deduction



       observations                        prediction
                                revision


specific instances                            individual events
Sir Isaac Newton:
(1643-1727)
Cosmology as a
Science


• Mathematical description
  of the Universe

• The same physical laws
  apply to earth and Universe
Newton: Fundamental contributions

•Mathematics: - series expansions
              - differential calculus
              - approximation methods
              -…
• Optics:     - spectral analysis of white light
• Physics:    - ‘Principia mathematica…’
• Astronomy: - derive Kepler’s laws from
                gravitational forces
• …..
A toy universe

                           constant density
                           (homogeneous)


                          boundary

According to Newton, what is going to happen ?
 The model Universe is going to collapse under
  its own gravity
Newton’s Conclusion:
 In order to avoid collapse
    homogeneous

    isotropic

    infinite size

    no center

 infinite in time
    has always been

    will always be

       perfect cosmological principle
The perfect cosmological principle
 homogeneous: the universe looks the same
                   everywhere on large scales
           there is no special place (center)
 isotropic: the universe looks the same in all
            directions on the sky
          there is no special direction (axis)
 unchanging: The universe looks the same at
                all times
                there is no special epoch
Olber’s Paradox
• If the universe is i) eternal
                     ii) (more or less) uniformly filled
                        with stars
                     iii) infinite


• then there is a star along each line of sight

so:      Why is the night sky dark ?
Problems with an infinite universe
   Olber’s Paradox: Why is the night sky dark?


                       Shell of radius r1:= 2r1 :
                                          3 4r
                                          2
                       Surface: S1=4 r12 1)2
                                    3
                                    2       (4r
                                            (2r
                       Volume: V1=4 r12x x
                                    3
                                    2       (2r1)2
                                            (4r
                       # of stars: N1= 4  r12x x
                                      3
                                      2         (2r1)2
                                                (4r
                       luminosity per star: l*/4 /16
                       luminosity of shell:
                         L1 = 4  r12x x l*/4
                           3
                           2          (2r1)2 l* /16
                                      (4r
                             = 4  r12x l* = L1
 Olber’s Paradox:

                     Each shell contributes

                       L1 = 4  r12x l*

                     infinite number of shells
                      infinite luminosity


(at least) one of the assumptions must be wrong !
How to solve Olber’s paradox ?
 Universe is finite
 Universe has finite age
 The distribution of stars throughout space is
  not uniform
 The wavelength of radiation increases with
  time

Note: for the big bang model, all these
     conditions are satisfied
Einstein:
• speed of light = const
        relativity of
        simultaneity,
     special relativity

• general relativity:
  space-time is curved

• prediction of black holes
• prediction of gravitational waves
 Einstein
• Universe has to be static!
• only possible if extra-term is included in
  equations to counter-balance attraction
           cosmological constant

• Einstein’s “biggest blunder”
Edwin Hubble
(1889-1953)
Four major accomplishments
in extragalactic astronomy
 The establishment of the
   Hubble classification
   scheme of galaxies
 The convincing proof that galaxies are island
   “universes”
 The distribution of galaxies in space
 The discovery that the universe is expanding
Doppler effect (for light)
 The light of an approaching source is shifted to the
 blue, the light of a receding source is shifted to the
 red
Doppler effect
The light of an approaching source is shifted to the blue,
the light of a receding source is shifted to the red.




       blue shift                  red shift
 Doppler effect


redshift:

    obsem
 z
       em
z=0: not moving
z=2: v=0.8c
z=: v=c
The redshift-distance relation
Key results
 Most galaxies are moving away from us
 The recession speed v is larger for more
  distant galaxies. The relation between recess
  velocity v and distance d fulfills a linear
  relation:
              v = H0  d
 Hubble’s measurement of the constant H0:
          H0 = 500 km/s/Mpc
 today’s best fit value of the constant:
          H0 = 71 km/s/Mpc (WMAP)
Question:
If all galaxies are moving away from us,
does this imply that we are at the center?

Answer:
Not necessarily, it also can indicate that the
universe is expanding and that we are at no
special place.
Einstein’s General Relativity +
observation of expanding Universe:



 Universe started from a point:



          “Big Bang Model”
Big Bang Model
Big Bang in a nutshell:
Cosmological redshift
   While a photon travels from a distant source
    to an observer on Earth, the Universe
    expands in size from Rthen to Rnow.

   Not only the Universe itself expands, but
    also the wavelength of the photon .
                         Rnow
           received          emitted
                         Rthen
Cosmological redshift
   General definition of redshift:
             received  emitted
          z
                   emitted

     for cosmological redshift:

                     received     Rnow
          1 z                  
                      emitted     Rthen
A large redshift z implies ...
 The spectrum is strongly shifted toward red
  or even infrared colors
 The object is very far away
 We see the object at an epoch when the
  universe was much younger than the present
  day universe
 most distant astrophysical object discovered
  so far: z=5.8
 z>5.8: “dark ages”
Are there any indications that this
picture is correct?

   Yes !

       Primordial Nucleosynthesis

       Cosmic Microwave background
     Primordial Nucleosynthesis
       Georgy Gamov (1904-1968)
   If the universe is expanding, then
    there has been a big bang
   Therefore, the early universe must
    have been very dense and hot
   Optimum environment to breed the elements by
    nuclear fusion (Alpher, Bethe & Gamow, 1948)
      success: predicted that helium abundance is 25%

      failure: could not reproduce elements more massive

        than lithium and beryllium ( formed in stars)
The Cosmic Microwave
Background (CMB)
Last scattering surface   transparent




                             opaque
Penzias and Wilson 1965
 Working at Bell labs
 Used a satellite dish to measure radio
  emission of the Milky Way
 They found some extra noise in the receiver,
  but couldn’t explain it
   discovery of the background radiation
 Most significant cosmological observation
  since Hubble
 Nobel prize for physics 1978
The cosmic microwave
background radiation (CMB)
 Temperature of
  2.728±0.004 K
 isotropic to
  1 part in 100 000
 perfect black body
 1990ies: CMB is
  one of the major tools to study cosmology
 Note: ~1% of the noise in your TV is from
  the big bang
More results from the CMB
                  The Earth is moving
                   with respect to the
                   CMB  Doppler shift

                  The emission of the
                   Galaxy


                  Fluctuations in the
                   CMB
•Fluctuations in CMB responsible for
structure formation in the universe
Cosmic Structure formation
           New developments:
          Science discovery of the year 1998
                                         q0 = 0
                                         q0 = 0.5

                                      Data indicates:
                                      q0 < 0
                                       Expansion
fainter




                                      is accelerating


                                      more distant
From Supernova observations:

 The expansion of the universe is
  accelerating !!!
 But gravity is always attractive, so it only
  can decelerate

   Revival of the cosmological constant 
The fate of the Universe for >0

k=+1
                              >0




                              =0
   Wilkinson Microwave
   Anisotropy Probe (WMAP) (2003)




COBE (1992)       WMAP (2003)
Summary of most important results of
            WMAP

• Age of the Universe: 13.7 billion years
• First stars:         200 million years
                       after Big Bang
• CMB:                 decoupled 379 000 years
                       after Big Bang
• Hubble constant:     H0= 71 (km/s)/Mpc
• Content of the Universe:
                        - 4% Atoms
                        - 23 % cold, dark matter
                        - 73 % ‘Dark Energy’

				
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posted:12/9/2012
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