current by liwenting


									final exam!!!
 Today we will discuss Cosmology and the Big
 Wednesday we will finish the Big Bang, have a
  short discussion of Life in the Universe, and
  review for the final exam
 Remember:
AST 1002
      Planets, Stars and Galaxies
      Expanding Universe
                                                   “the Great Wall”
Today‟s Lecture: purpose & goals
1)   Hubble‟s Law                                           Virgo
2)   Expanding Universe
3)   Cosmology Assumptions
                                    Looking at an „empty patch of sky
4)   The Origin of the Universe
     “the Big Bang”
5)   Fate of the Universe
        Galactic Clusters – II
   SuperClusters
       On even greater scales the galaxy clusters themselves form
        clusters called superclusters that can be tens to hundreds
        of millions of light years across.
       These superclusters resemble
          “…the froth on soap bubbles…”       Virgo III
        in space.
                                                             10 million ly
       Between them lie great voids
          containing relatively few galaxies.

                                  Local   Canes
                       Sculptor           group

                                                          Ursa Major
                                              Leo I         group

             Fornax                                                 Leo II
             Cluster                                                group
            Galaxy Collisions
   Occasionally galaxies collide
       Happens most often in centers of rich
        galactic clusters
       Stars that make up the galaxies don‟t
        actually slam into each other
   Passage of one galaxy through/near
    another causes major “stirring”
       due to gravitational interaction
   Causes new activity such as               Think of walking around
                                           before or after a football game
       huge burst of
        star formation,
       creation of

                          slow rotation
         Pop II           very little gas and dust
                          no new star formation!!

         Pop II       fast rotation

         Pop I
                      significant gas and dust – in arms
                      significant new star formation!!
                        (in the spiral arms, spherical
                        component older!!)

                  small, irregular, no rotation
                  some gas and dust
                  some new star formation (randomly
                   throughout galaxy)
             Measuring Distances
   Stereoscopic viewing (Parallax)
       only “small” distances
            nearest few thousand stars in our galaxy
   “Standard candles”
       objects which have „known‟ luminosities
       Cepheid variables
          variation tells luminosity – good to 65-100 million LY
       brightest stars in galaxy, size of HII regions, overall brightness of
        galaxy – good in steps out to 1-2 billion LY
       Type Ia supernova
            all have same luminosity
            good to 8-10 billion LY (a few measured
             as far away as 12-13 billion LY)

       Relies on Comparison to examples of the
        same type objects in nearby galaxies
                              History reminder
                              – “Island Universes”
                                       Andromeda galaxy

   1924 – Edwin Hubble                                   size of the Moon

       Measured the distances to
        several galaxies using the
        relationship of Cepheid
        variables, discovered by
        Henrietta Leavitt (1912).
        (Cepheid variables)
       This was conclusive
        proof that the galaxy
        lay well beyond the
        Milky Way.  2 million l.y.
       The universe was much larger
        than previously thought.
                                                    Andromeda galaxy

           Distance Modulus

   Calculate the distance to the Andromeda
    Galaxy using Hubble‟s method.
       m - Mv = -5 + 5log10(d(parsecs))

                                    Luminosity-Period Relation of Cepheid Variables
           Galactic Redshifts
     Edwin Hubble (1889-1953) and colleagues
          measured the spectra (light) of many galaxies
          found nearly all galaxies are red-shifted
     Redshift (Z)
              lobserved - lrest                            Andromeda galaxy
     From Ch. 2,
      (Doppler effect) Z = v/c
      (for speeds approaching c,
      we‟ll need a relativistic version
      of this equation.)
Z = [(1+ v/c)/(1+ v/c)]1/2 - 1
                           Hubble‟s Law
   Hubble found the amount of redshift depended upon
    the distance
                          the farther away, the greater the redshift
    Recessional velocity

                                                    v = H0 x d

                              Hubble’s data         What is H0?
                               distance to galaxy
    Bigger Structure
   Structure bigger than galaxies
   Galaxy groups
       2-30 galaxies
       Local Group – contains the
        Milky Way
   Galaxy clusters                                     Earth
       100s of galaxies – Virgo                                      Cluster

        Cluster (rich cluster)
   Superclusters
       groups and clusters combined
   The Universe is filled with
    large scale structure
       “walls” and “filaments”
        separated by great voids – (like
        froth on soap bubbles)        First detailed study done by Margaret Geller & John Hucra,
                                               Harvard-Smithsonian Center for Astrophysics
         Hubble‟s Law
   Holds for essentially all galaxies with measured redshift
    and distance
   THEREFORE, measuring the redshift tells us the distance
       redshifts up to 95% of the speed of light have been measured!!
          ultraviolet wavelengths can be shifted into the visible, or infrared

   H0 is Hubble‟s constant = 70 km/(s Mpc)
       Mpc = megaparsec
   If everything is moving away from us and things farther are
    moving faster
   Then the Universe is expanding!
    This doesn‟t mean what you are probably
      thinking . . . .
                Expanding Universe
           Space itself is expanding, not matter flying
            apart within space.
           Examples:
               dots
               rubber band
               raisin bread
               ants on a balloon

   It does not mean we are at the center
    of the Universe
            every part of the Universe sees everything
             moving away from it
        Cosmological Redshift

   We now know 3 kinds of
   Doppler shift
       due to motion
   Gravitational shift
       due to distortion of space-time by mass
   Cosmological shift                                       lobserved - lrest
        due to stretching of space                        Z=
          not due to relative motion

       as space stretches, the wavelength stretches
        and becomes longer
        Relativistic (near speed of light):   Non-relativistic (<0.05c):

        Z = [(1+ v/c)/(1+ v/c)]1/2 - 1        Z = v/c
        Looking Back in Time
   Remember it takes time for light to
    reach us
       travels at 300,000 km/s
       So we see things “as they were” some time
   The farther away, the further back in
    time we are looking
       1 billion LY means looking 1 billion years
        back in time
   So the greater the redshift, the further
    back in time
       redshift of 0.1 is 1.4 billion lightyears which
        means we are looking 1.4 billion years into
        the past
        Thinking Back in Time
   If all galaxies are moving away from
    each, then in the past all galaxies were
    closer to each other.
   Going all the way back, it would mean
    that everything started out at the
    same point
       then began expanding
   This starting point is called the Big Bang
   We can calculate the age of the
    Universe using Hubble‟s Law
    v = H0 x d             d = v/H0               thubble = 1/H0
           But     distance = rate x time
           (the time here is how long the expansion has been
           going on  The Age of the Universe)
         Big Bang
   At the beginning of our Universe,
    all matter was together in a very
    compact form
       matter was nothing like it is now
       very “hot”
   Then space started expanding
       things “cooled”
       eventually it was possible for normal
        matter to “condense” out of the hooter
   Big Bang model makes a number of
    testable predictions….
   …continued!
        At the Beginning

   Originally all the energy (and
    matter) of the Universe was
    condensed into an incredibly small region
       MUCH smaller than the size of a proton
   Energy, matter, space and time were all very different
    than today
       need a new “theory of everything” to understand
          not yet possible

          11-dimensional space??? (models are very weird)

   During early expansion, space-time and gravity became
    separate from energy and mass
       particles and antiparticles were being created from energy and
        annihilating into energy all the time
        Glow of the Universe

   The early Universe was very
    hot and dense
       glowed with blackbody
       but so dense the light kept
         getting absorbed (opaque)
   Eventually the Universe
    cooled enough to form hydrogen atoms
       blackbody radiation could now travel freely
       That time called “recombination of the Universe”
   Light from that time should be all around us
    and be detectable.
       3K background radiation
                 Cosmic Microwave Background
   This light should be cosmologically
       Mostly into microwave region
   CMB was first seen in 1960s
       Pensias & Wilson
        (Bell Labs)
          – won Nobel prize
            in physics for this

       twenty years after prediction
   COBE satellite mapped the CMB
       measured the spectrum
       wonderful match between theory and data
         Temperature = 2.73K
       cooled glow from recombination era.
       Incredibly uniform across sky.
        Composition of Light Elements
   Big Bang model predicts the percentage of light
       Hydrogen (1H), deuterium (heavy hydrogen, 2H), helium
        (4He), lithium (7Li), beryllium (9Be), boron (10B and 11B),…
       elements formed before recombination (created out of
       percentages depend upon density and temperature of
        early Universe, and how fast it cooled.
   Observed percentages agree with Big Bang model
       Almost all was created as hydrogen (1H) and helium
        (4He), with only trace amounts of anything else.
           must have cooled from                               Helium

            something very hot.
          Fate of the Universe
   The Universe is expanding
   But gravity should be pulling it back in
   So what should the Universe‟s fate be:
       Continue expanding forever
       Have expansion keep getting slower forever and stop at infinite
       Expansion stops and eventually Universe collapses upon itself
   These possibilities are called
       open universe
       flat universe
       closed universe
          Enough Matter?
   The amount of matter in the Universe helps determine its
       if there is enough mass, gravity wins
       given H0 = 70 km/(s Mpc), critical mass density is 8x10-27 kg/m3
   define MASS as the actual density of mass in the Universe
    divided by the critical density
       MASS < 1 is an open universe
       MASS = 1 is a flat universe
       MASS > 1 is a closed universe
         Enough Matter?
   Visible matter (stars in galaxies, & hot gas)
       only 2% of critical density; MASS = 0.02
   Dark matter in galaxies
       (measured by galaxy rotation curves)
       about 10 times as much; MASS = 0.2
   Dark matter between galaxies
     (measured by watching galaxies fall
        inward in galactic clusters and
        from gravitational lensing)
     raises total to 30% of critical density

     MASS = 0.3

   We do not observe enough matter to cause
        the Universe to be closed
   But it‟s not the end of the story…
               Is the Expansion Slowing Down?
       Use Type 1a supernovae
           a standard candle
           use brightness to determine
           use redshift to determine speed
           compare them
           data lies below prediction (galaxies
            are speeding up!!)

       Answer: Strangely enough…
        the rate of expansion is speeding up!
         Formation of Structure
   (early in the Universe)
   Normal matter was spread fairly
       due to interactions and radiation
   Dark matter was not distributed
       clumps remained
   Expansion spread things out
       but gravity held large clumps of dark matter
   Dark matter attracted normal matter
       source of galaxies and structure

To top