Structure of the Universe

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Structure of the Universe
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Learning GoalsWhat We Should Know

• Distance and Velocity of Galaxies
• Hubbles law
• Evidence for the Expanding Universe
• Mass of the Universe, Open vs Closed, Dark Matter
• Theories for the Origin of the Universe
• Age fo the Universe

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19 Cosmology the Universe

• Reading Assignments
• Pathways to Astronomy, Schneider Arny
• Units 79 -82
• Online Resources Course Website

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Cosmology

• Olbers Paradox
• Why is the sky dark
• Brightness decreases at 1/d2
• Area (? Number of stars) should increase as d2
• Sky should be bright
• Assumptions
• Universe is infinite
• Universe is infinite in age
• Universe is static

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Red Shift Velocity of Galaxies
Object Distance (Mpc) Redshift Velocity (km/s)
Cepheids 15 0.003 1,070
Blue Giants 60 0.014 4,290
Globular Clusters 60 0.014 4,290
H II Regions 150 0.035 10,740
Galactic Clusters 1200 0.28 85,890
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Distance to Galaxies
Object M Maximum Distance (Mpc)
Cepheid Variables -5 15
Blue Giants -9 60
Globular Clusters -9 60
H II Regions -11 150
Cluster Method (galactic clusters) 1200
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Recession of GalaxiesHubbles Law

• Edwin Hubble (1920s)
• Relationship between distance and recession
  velocity of galaxies
• V H D
• H is Hubbles Constant
• H V/D ( km s-1 Mpc-1)

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Hubbles Constant
Distance (Mpc) Velocity (km/s) H (km s-1/Mpc)
15 1,070 70
60 4,290 70
150 10,740 70
600 42,945 70
1200 85,890 70
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Expanding Universe

• Cosmological Principle
• Universe should look the same from any
  observation point
• Distribution of objects (galaxies, clusters of
  galaxies, etc. should be the same)
• Perfect Cosmological Principle
• Universe should appear the same no matter when it
  is observed (now or 5 billion years ago)

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Expanding Universe

• Redshift (recession velocity) increases with
  increasing distance
• Observation is the same in all directions from
  the earth
• Observations at greater distance are observations
  at earlier times (look back time)

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Theories of the Universe

• Steady State
• Universe always looks the same
• As galaxies spread out, new galaxies are formed
  in the vacant regions
• Universe has no beginning or end

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The Big Bang

• Universe originates from a singularity
• Rapid release of energy (explosion)
• 3 possible universes
• Open, expansion slows down but will continue
  forever, gas and dust is used up, universe burns
  out
• Closed, expansion slows, stops and contraction
  begins, Universe collapses
• Flat, expansion slows so it is essentially zero
  when the age of the universe is infinite

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Rejection of the Steady State Model

• 3oK background radiation
• Quasars
• 3oK background radiation
• Radio telescope observations of the universe
• A persistent level of background radiation
• Level of radiation was same in all directions
• Background radiation could be explained as the
  remnant from the big bang cooled due to
  expansion 3oK
• Steady state universe cannot explain this

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Quasars

• Quasi-Stellar Objects
• Strong radio emissions
• Revealed by moon occultation of source
• Stars - not normally strong radio sources
• Object with size of star and strong radio
  emissions
• Spectral observations showed bright emission
  lines in visible

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Quasars

• Red shifted lines of hydrogen
• Red shift is 0.156
• Formation of black hole at center of galaxies
• About 6.5 billion light years away
• Dont exist closer or further away
• Universe in not uniform, i.e. steady state is not
  valid

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Open Versus Closed Universe

• Examine 4 different areas to answer this question
• Mass of the Universe
• Amount of deuterium
• Age of the Universe
• Recession rate versus distance

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Mass of the Universe

• Mass is the crucial factor in determining state
  of the Universe
• Critical Density ?c
• ? lt ?c open universe
• ? gt ?c closed universe
• ? ?c flat universe
• ?c 4 x 10-30 g/cc (grain of sand in volume of
  earth)

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O

• O is ratio of observed density to critical
  density,
• O ?/?c
• O lt 1.0 open universe
• O gt 1.0 closed universe
• O 1.0 flat universe
• 1980s estimate of density of universe
• ? 4 x 10-31 g/cc, O 0.1 (open universe)

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Dark Matter

• Non-luminous matter in the Universe
• Suggested by rotation of galaxies and excess
  rotation in galactic clusters
• Gravitational Lensing
• Massive objects can bend light that passes near
  them
• Lensing effect displacement of images
• Proved in solar eclipse of 1919

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Sources of Dark Matter

• Earth like objects
• Required number of objects two great
• Massive Compact Halo Objects (MACHOS)
• Black hole type objects in galactic halos
• Some observations of gravitational lensing, rate
  to small to account for dark matter
• Weakly Interacting Massive Particles (WIMPS)
• Predicted nuclear particle, not yet detected
• Neutrinos massless nuclear particles
• Might have very small mass?

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Deuterium

• Form of hydrogen with 1 proton and 1 neutron in
  nucleus
• Fate of deuterium
• 1H1 1H1 1H2
• 1H2 1H1 2He3
• 2He3 2He3 2(1H2) 2He4
• 1St reaction is very slow (probability is once
  per 14 billion years in a star)
• Second reaction very fast (once per 6 seconds)

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Deuterium

• Hence deuterium does not build up in stars
• Present ratio of deuterium to hydrogen is about 1
  per 100,000
• This deuterium was produced in the big bang
  (origin of the universe)
• The existence of this high ratio suggests a low
  density of normal mass as the universe formed
• Supports an open universe (doesnt account for
  dark matter)

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Age of the Universe

• Oldest Globular Clusters have ages of 12-13
  billion years
• Estimates of age of universe depend on history of
  expansion
• Use Hubbles constant to estimate age of
  universe
• age 1/H
• Age 1/( 70 km s-1/Mpc) 13 billion years

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Age of Universe

• Flat Universe expansion rate is constant, age
  estimate is OK
• Open Universe expansion rate is slowing
  slightly age is a little over estimated
• Closed Universe expansion rate has decreased
  significantly age is over estimated
• Using age of oldest Globular Clusters
• Universe is open
• Or Hubbles constant less that 70 km s-1/Mpc

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Recession Rates

• History of recession velocities
• Highest in past for closed universe
• Intermediate for open universe
• Constant for flat universe
• How to connect recession velocities with distance
  or time for earliest universe
• Use Type 1a supernova to get distances
• Type 1a binary system with white dwarf drawing
  mass from companion and brightening

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Type 1a Supernova

• Type 1a supernova does not have hydrogen in its
  spectra
• All Type 1a supernova has about the same
  brightness since the white dwarf is about 1.4 Ms
• Results for Type 1a supernova show the recession
  rate in the past is actually less than now
  suggesting open or flat universe

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What is the BB

• Origin of the Universe from a singularity
• All matter, energy, time and space created from
  the singularity
• Universe evolves from the singularity event (i.e.
  the Big Bang)
• Observational Evidence
• Recession of galaxies
• Helium abundance
• Background Radiation

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• Helium abundance
• Only abut 10 from stellar fusion
• 25 in universe
• Helium formed in the big bang
• Background Radiation
• Red shift of radiation from the big bang due to
  expansion
• Predict a uniform background of radiation at a
  temperature of about 3K

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Synthesis of Elements

• Initial state of Big Bang temperature of
  several billion degrees
• To hot for nuclei to form
• Universe made up of photons, protons, neutrons,
  electrons, and neutrinos
• Mostly photons (109 to 1) , radiation dominated
• Small volume (size of sun)
• Expansion and cooling (T 109 K)
• Nuclei can begin to form

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Nucleosysthesis

• Deuterium (pn) 2H
• Tritium (p2n) 3H
• Helium 3 (2pn) 3He
• Finally 4He
• 4 minutes to convert particle in to He (25)
• Over next 30 minutes synthesis of lithium and
  beryllium
• No further synthesis (density and temperature too
  low)

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Radiation Dominated Phase

• Expansion
• Hot, electrons are free
• Density and temperature decrease
• T in range of 106 K after 1 year, x-rays
• T 105 K after 1000 years, UV photons appear
• Expansion, redshifting of radiation

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Matter Dominated Universe

• At 104 years universe becomes matter dominated
• Radiation matter density decrease, radiation
  density decreases faster due to redshifting
• Decoupling of matter and radiation
• 300,00 years, T3000 K
• radiation redshifted to visible light
• Atoms can form (hydrogen)
• Radiation is largely free to travel without
  interaction
• Universe becomes transparent

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3K Background Radiation

• COBE Cosmic Background Explorer
• WMAP (Wilkerson Microwave Anisotropy Probe)
• Small variations in microwave background
• ( 7 x 10-6 K) starting point for galactic
  formation
• Gravitational forces begin to act after
  decoupling
• Galaxies form in about 300 to 500 million years
  after decoupling

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Big Bang The Very Beginning

• Inflation
• In the time frame of 10-35 to 10-33 seconds after
  big bang
• Rapid expansion of the universe by a factor of
  1040
• Inflation from smaller than a proton to larger
  than the observed universe would produce
  isotropic condition, i.e. smooth universe,
  isotropic microwave background

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Inflation

• Curvature of Space
• Inflation accounts for flatness of space and the
  flat universe

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Curvature of Space

• If we observe that the universe looks the same in
  all directions it must have a constant curvature
• 3 possibilities
• Positive curvature, look like a sphere,
  corresponds to a closed universe
• Zero curvature a plane expanding forever, flat
  or open universe
• Negative surface turns away from itself, open
  universe

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Questions