P1246990942YRJqK

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Exploring the Universe withGEMS Digital
AstronomySession V Cosmology
Sponsored by the Department of Astronomy The
National Center for Supercomputing
Applications University of Illinois at
Urbana-Champaign With funding provided by NASA
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Recall from last time

• We can spread out the light from an object and
  see its spectrum

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Different elements produce unique emission lines!
Neon
Mercury
Sodium
Image Credit scifun.chem.wisc.edu/chemweek/gasemi
t/gasemit.html
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• Different kinds of spectra

Absorption line spectrum
Emission line spectrum
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Recall from last time

• We can plot the spectrum like this

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Types of Spectra
Stellar (Star) Spectrum
Continuum Emission
Image credit Sloan Digital Sky Survey
Collaboration
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Types of Spectra
Galaxy Spectrum
Narrow emission lines
Image credit Sloan Digital Sky Survey
Collaboration
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Types of Spectra
Quasar Spectrum
Broad Emission Lines
Image credit Sloan Digital Sky Survey
Collaboration
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Hubbles Discovery
Edwin Hubble (1889-1953)
Hubble noticed something odd about the absorption
lines in galaxy spectra he observed The calcium
absorption lines seemed to shift!!
Five spectra adapted from Hale Observatory
originals
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Redshifting

• Objects moving toward us appear more blue, while
  objects moving away from us appear more red!

Image Credit www.cnrt.scsu.edu
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Redshifting of Spectra
Image Credit http//www.sdsu-physics.org
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Redshifting of Galaxies
Light from a galaxy moving slowly away from Earth
Light from a galaxy moving faster away from Earth
Image Credit herschel.jpl.nasa.gov
www.cnrt.scsu.edu
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Redshifted Spectra
Wavelength (nm)
Very Distant Galaxy
Distant Galaxy
Nearby Galaxy
Nearby Star
Image Credit www.cnrt.scsu.edu
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Redshifted Spectra
Three of the most distant quasars discovered by
the Sloan Digital Sky Survey
RED
BLUE
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Hubbles Law

• All galaxies move away from us!
• The farther away, the faster they move!
• So, are we at the center
• of the universe???

Edwin Hubble (1889-1953)
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Hubbles Law

• All galaxies move away from us!
• The farther away, the faster they move!
• So, are we at the center
• of the universe???

Edwin Hubble (1889-1953)
Animation credit www.einstein-online.info
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How can we measure the expansion of the universe?

• Well need measurements of distance and velocity
  for a number of galaxies.
• Lets start by finding distances to galaxies we
  see

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Measuring Distances

• Nearby galaxies appear large and
  bright
• While distant galaxies appear small
• and faint

Image Credit Sloan Digital Sky Survey
Collaboration
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Measuring Distances

• If distant galaxies appear more faint then we
  can estimate the distances to galaxies by
  measuring their brightness!
• But careful!
• This is not quite right since we have assumed
  all galaxies are equally bright to begin with.
• For our purposes today.. This will be close
  enough.

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Measuring Brightness

• Remember from earlier
• We measure brightness in units called
  magnitudes

Recall. this is basically a measurement of how
many photons from the star or galaxy that we
capture with our camera.
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Magnitudes

• Backwards-scaling measurement (opposite what you
  would guess!!)
• BRIGHT objects large NEGATIVE magnitudes
• Suns magnitude -26.0
• Brightest star in night sky -1.5
• FAINT objects large POSITIVE magnitudes
• Faintest objects seen with your eye 6.0
• Faintest objects in our digital survey 23.0

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How can we measure the expansion of the universe?

• Next we need a way to measure the velocity of
  these galaxies.
• Recall from earlier.

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The Power of Redshift!

• Redshift gives us a measurement of the galaxys
  velocity!
• Now we have everything we need to measure the
  expansion of the universe!

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So we can make a diagram like Hubbles!
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Cosmology!

• So weve convinced ourselves that the universe
  is expanding
• What does that mean???

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Einsteins View

• The Universe has no center..
• It looks the same in each direction from
  anywhere.
• The Universe is expanding!

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Penzias Wilson

• 1964 Arno Penzias Robert Wilson, working to
  improve radio detectors, find a peculiar kind of
  noise in microwave radiation coming from all
  directions on the sky
• Explanation Pigeon droppings on the antenna? Or
  REAL radiation??

http//www.bell-labs.com/project/feature/archives/
cosmology/
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Cosmic Microwave Background Radiation!
Shows that the universe is nearly the same
temperature in every direction. Indicates a
massive explosion-like event occurred in the
universe about 13.7 Billion years ago!
http//www.astro.cornell.edu/rbean/images/cmb_pop
up.jpg
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The BIG BANG!

• Evidence
• The universe is expanding.
• The amount of gas in the universe matches with
  what should have been created by a big bang.
• We see dim microwave radiation coming from every
  direction an afterglow!

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The Big Bang Expansion
Credit NASA/STScI/G. Bacon
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So, where did the Big Bang happen??

• Everywhere!!
• We know because the Universe is
• Homogeneous (same composition everywhere)
• Isotropic (looks the same in all directions)

Homogeneous
Isotropic
Image Credit www.astro.ucla.edu/wright/cosmo_01.
htm
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Formation of Structure!

• The Universe began very hot dense following the
  Big Bang.
• As it expanded and cooled, large clouds of gas
  could be compressed by gravity, forming stars and
  galaxies..

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Theoretical Models

• With the help of supercomputers, astronomers can
  apply our knowledge of physics to create models
  of how large-scale structure formed in the
  universe.

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Credit http//qso.lanl.gov
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Credit http//qso.lanl.gov
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Credit http//qso.lanl.gov
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Large-Scale Structure
So, thats the theory.. But what does it really
look like??
Data from the Sloan Digital Sky Survey allow us
to make a detailed 3D map of the universe!
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SDSS video
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Fate of the Universe

• Three Suggested Possibilities
• 1. Continued expansion Big Freeze
• 2. Expansion accelerates.. Big Rip!
• 3. Gravity overcomes the expansion.. Big
  Crunch!

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Continued expansion comes from Dark Energy!
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Credit NASA/CXC?M.Weiss
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Big Freeze?
Credit NASA/STScI/G. Bacon
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Big Rip?
Credit NASA/STScI/G. Bacon
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Big Crunch?
Credit NASA/STScI/G. Bacon
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What do you think??

• Intuitively, you might guess

Gravity might cause the universe to slow in its
expansion and eventually reverse in direction to
collapse back down So, a Big Crunch??
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Current Data Suggests

• The Universe is actually ACCELERATING!!
• Big surprise to everyone!
• How do we explain this??
• Dark Energy a theoretical repulsive force that
  seems to counter-act gravity on large scales

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Fate of the Universe

• Not enough matter in the Universe to cause a Big
  Crunch
• Dark Energy is not really understood but its
  existence implies
• Stronger repulsion as things get farther away
• At present, the Universe looks like it will
  expand forever!

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The Big Freeze!
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The Big Freeze

• The Universe continues to expand and cool until
• Everything becomes very dark and cold
• Eventually there will be no more galaxies or
  stars in the night sky! (

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The Big Freeze