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GenGeoAstroII Cosmology


									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”),
            - 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:
• 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

        Mythology and Modern
 Ancient

 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

specific instances                            individual events
Sir Isaac Newton:
Cosmology as a

• 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


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

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

• general relativity:
  space-time is curved

• prediction of black holes
• prediction of gravitational waves
• 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
Four major accomplishments
in extragalactic astronomy
 The establishment of the
   Hubble classification
   scheme of galaxies
 The convincing proof that galaxies are island
 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
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


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
              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)
If all galaxies are moving away from us,
does this imply that we are at the center?

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 .
           received          emitted
Cosmological redshift
   General definition of redshift:
             received  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

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

                  Fluctuations in the
•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

                                      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


   Wilkinson Microwave
   Anisotropy Probe (WMAP) (2003)

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

• 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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