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Cosmology

Cosmology. That part of astronomy which deals with the nature of the universe as a whole. Olber’s Paradox (1826). Why is the night sky dark?. Olber’s Paradox (1926). Why is the night sky dark?. Olber’s Paradox. Why is the night sky dark?. The universe has an edge

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Cosmology

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  1. Cosmology That part of astronomy which deals with the nature of the universe as a whole

  2. Olber’s Paradox (1826) Why is the night sky dark?

  3. Olber’s Paradox (1926) Why is the night sky dark?

  4. Olber’s Paradox Why is the night sky dark? • The universe has an edge • The stars and galaxies ‘run out’ at some distance from us • The universe has a beginning • ...but the universe would be brighter earlier on.... • Light is redshifted (‘cooled’) by the expansion of the universe First suggested by Edgar Alllen Poe in 1848

  5. Hubble’s Law • Galaxies are moving away from us at a speed • proportional to their distance • V = H × d • H is called Hubble’s constant

  6. Hubble’s Law • Best estimate of H so far puts the age • of the universe at 13.6 billion years

  7. The Big Bang • Hypothesis: throughout the history of the universe, the galaxies have been moving away from each other . • - There was a time in the past where the universe was extremely dense and hot: the universe today evolved from this initial state, which we refer to as the ‘Big Bang’ • - The Big Bang does not occur in one place in the universe – it occured everywhere

  8. The Big Bang • Prediction 1: Until about 300,000 years after the big bang, the universe was hotter than the surface of the Sun (5800K) • - As the universe cooled below this temperature, it should have released black body radiation (a spectrum like the one we get from the surface of the Sun) everywhere in the universe • - As the universe aged, this radiation will have been redshifted • - This radiation should still be here today, everywhere we look at microwave frequencies • - Calculations show that it should correspond to a temperature of 2.73 K (-270 degrees celsius).

  9. Penzias and Wilson (1960s, won 1978 Nobel Prize)

  10. COBE (1989)

  11. The Big Bang • Prediction 2: Using what we know about nuclear physics, we can predict what elements were created during the first thousands of years after the Big Bang, and in what proportion

  12. Initially, universe is a plasma

  13. … a cosmic ‘soup’ of charged particles

  14. PROTON NEUTRON ELECTRON

  15. 300,000 Years Later….. • Universe much cooler, atoms start to form….. • Hydrogen, Helium, normal ‘stuff’

  16. Universe is now a GAS

  17. Universe is now a GAS HELIUM HYDROGEN

  18. 75% H 25% He 0.01% Deuterium (Hydrogen with one neutron) 0.0000000001% Lithium, Beryllium How do we observe the amounts of different elements in the early Universe?

  19. Look-Back Time The further away we look, the further back in time we are seeing

  20. Globular clusters

  21. WMAP and Structure Formation (2002)

  22. GRAVITY!

  23. Gravitational Collapse • We started with a uniform gas • Some regions were slightly denser (hotter) • The denser regions had larger gravity and started to pull other particles towards them • The gaseous Universe began to look ‘clumpy’

  24. History (Figure from Wayne Hu) (Figure from WMAP team)

  25. History

  26. History CMB Foreground-cleaned WMAP map from Tegmark, de Oliveira-Costa & Hamilton, astro-ph/0302496

  27. Using CMB blobs as a standardizable ruler: Boomzoom 3 Open universe Inflation with  Guth & Kaiser 2005 (Science) + WMAP3 Inflation without  Cosmic strings

  28. History CMB Foreground-cleaned WMAP map from Tegmark, de Oliveira-Costa & Hamilton, astro-ph/0302496

  29. z = 1000 Boomzoom

  30. z = 2.4 Boomzoom Mathis, Lemson, Springel, Kauffmann, White & Dekel 2001

  31. z = 0 Boomzoom Mathis, Lemson, Springel, Kauffmann, White & Dekel 2001

  32. Dark Matter: Primary evidence Mass of the Milky Way • From Kepler’s third law, mass of galaxy is about 400,000,000,000 MSun

  33. We seem to be missing about 90% of the mass of the galaxy! • Most of it cannot be emitting or absorbing light • Astronomers name it Dark Matter

  34. Dark Energy and the Shape of the Universe • Type Ia supernovae always have the same brightness – if we know that brightness, • We can accurately measure the distance to them

  35. The Shape of the universe depends on what is in it... “Normal Matter” 4% Dark Energy 73% Dark Matter 23% ... Currently, it appears that the universe is close to flat

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