The Structure of the Universe

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The Structure of the Universe

• What is out there?

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A false color image of the universe Color coding
is related to how far away the galaxies
are blue is closest red is most distant 1.5
million galaxies observed in the infrared at
1-2.2 ?m 500 million stars from the Milky Way
http//spider.ipac.caltech.edu/staff/jarrett/index
-3.html
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Where Does the Structure Come From?

• The early universe was lumpy (inhomogeneous)
• Gravity caused the more dense regions to attract
  more matter from the less dense regions
• Also see structure in the microwave cosmic
  background radiation from the Big Bang

1992
2003
http//pancake.uchicago.edu/carroll/cfcp/primer/w
map-cobe.html
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Views from Hubble Deep Field

• Area of sky the size of a grain of sand at arms
  length
• Fuzzy stars are galaxies with hundreds of
  millions of stars
• Some of most distant objects seen in space

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Objects in the Universe

• Superclusters (clusters of clusters of galaxies)
• Clusters of galaxies
• Galaxies
• Stars (with or without planetary systems)
• Planets
• Moons
• Minor Planets (Pluto!)
• Asteroids
• Comets

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Whats In Between the Stars and Galaxies

• Hydrogen and Helium gas
• Leftovers from the Big Bang
• Dust
• Remnants of stars that exploded
• Contains heavier elements
• All the matter in the universe recycles to form
  new galaxies and stars!

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Measuring Distances in the Universe

• Distances are enormous!
• Unit of length is the light year
• Distance light travels in one year
• Speed of light 3.00 X 108 m/s
• 1 ly 9,500,000,000,000,000 m9.5 X 1015 m

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Looking Into the Past

• It takes time for light to travel from the most
  distance objects to reach us
• If a star is 1 light year away in distance, it
  took 1 year for the light to travel that
  distance.
• The light we see from stars 200,000 light years
  away was emitted 200,000 years ago

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Irregular Galaxies

• No well defined shape or structure
• May be all dust and gas, and has not yet formed
  many stars
• Some have little or no dust or gas

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Elliptical galaxies

• Egg shaped
• Older than spirals
• Contain little gas and dust
• Stars are redder

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Spiral Galaxies

• Arms have gas and dust
• New stars form in the arms
• Young stars are hotter and bluer

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Our Galaxy The Milky Way
As seen from Earth
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Our Galaxy The Milky Way
Side View Simulation
Top View Simulation
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Life Cycle of Galaxies

• 1.5 Billion Years ABB
• Matter clumps into strands
• Protogalaxies form
• 2.6 Billion Years ABB
• Strands are more defined
• Irregular galaxies form
• 5.0 Billion years ABB
• Strands become chains of galaxies
• Ellipticals form from irregulars
• Collisions of galaxies

http//antwrp.gsfc.nasa.gov/apod/ap951108.html
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Life Cycle of Galaxies

• 7.4 Billion Years ABB
• More matter falls into strands
• Giant elliptical galaxies form from collisions
• As galaxies grow, they develop more structure
• Spirals form
• Spirals collide
• Form bigger ellipticals, arms are stripped off
• If enough gas is around, new arms form
• Eventually all gas is used up, left with
  ellipticals

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The Galaxies in the Local Group
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Super Clusters

• Largest objects in the universe
• Groups of galaxies are drawn together by gravity

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The Big Problem

• Galaxies in clusters are moving faster than they
  should given the amount of mass in the stars and
  other visible objects
• There has to be more mass out there than what we
  can see

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Possible Answers

• Dark Matter
• MACHOS-massive compact halo objects
• WIMPSweakly interacting massive particles
• Neutrinostiny almost massless subatomic
  particles (only 1-2 of missing matter
• Dark Energy
• Force that counteracts gravity allowing universe
  to expand faster

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Experimental Observations Supporting the Big Bang
Theory

• Hubble
• The universe is expanding.
• On average all galaxies are moving away from each
  other.
• The ones furthest away are moving faster.
• Penzias and Wilson
• Cosmic background radiation left over from the
  big bang.

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Light Emitted from Stars

• Sharp peaks in spectrum due to emission by
  excited atoms
• Electrons drop to lower energy orbitals and emit
  photons at specific energies (frequencies)

Photons emitted at different distinct energies
Energy Levels in Hydrogen Atoms
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Doppler Shift

• Train whistle changes pitch as it moves past you
• Wave crests seem to bunch up when moving towards
  you (wavelength decreases)
• Wave crests spread out as train moves away from
  you (wavelength increases)
• The same thing happens with light!

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Hubble and the Redshift

• Galaxies that are further away are moving faster
  away from us!
• The faster they move the bigger the Doppler shift

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Velocity versus Distance
Farthest Stars move fastest!
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Cosmic Background Radiation

• As universe expands, wavelength of radiation gets
  bigger
• Visible light (nm) from early soup has been
  stretched to mm

http//background.uchicago.edu/whu/intermediate/i
ntermediate.html
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Cosmic Background Radiation

• Colors represent changes of 1/100,000 of
  background temperature
• Represent clumping in the early inflation of the
  universe

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Other Theories for the Universe

• Steady State Theory
• The universe is expanding but we can only see an
  observable part.
• Galaxies that move outside the observable
  universe are replaced by new galaxies formed
  inside
• The mass of the observable universe stays the same

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Other Theories for the Universe

• Pulsating Universe Theory
• The universe is currently expanding
• Gravity will eventually slow the expansion and it
  will reverse
• Everything will collapse back down to early Big
  Bang conditions
• The process will reverse because of the heating
  during collapse
• The universe will expand again
• Keep expanding and contracting