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Starry Monday at Otterbein

Welcome to. Starry Monday at Otterbein. Astronomy Lecture Series -every first Monday of the month- May 1, 2006 Dr. Uwe Trittmann. Today’s Topics. Introduction to Cosmology The Night Sky in May. On the Web. To learn more about astronomy and physics at Otterbein, please visit

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Starry Monday at Otterbein

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  1. Welcome to Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the month- May 1, 2006 Dr. Uwe Trittmann

  2. Today’s Topics • Introduction to Cosmology • The Night Sky in May

  3. On the Web • To learn more about astronomy and physics at Otterbein, please visit • http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Observatory) • http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)

  4. Cosmology • The part of astronomy (and astrophysics) that deals with the greatest structures in the universe – and the evolution of the universe itself! • The “start” of the universe, a primordial fireball  the early universe was very hot and dense  intimate connection between cosmology and nuclear/particle physics  “To understand the very big we have to understand the very small” Big Bang

  5. Questions, Questions, Questions • Scientists want to know, so they ask questions: • What is in the universe? • How do these things interact? • How does the universe change in time? • Is there a beginning? • Is there an end?

  6. What’s in the Universe? • Answers come from observations  Let’s observe:

  7. The Earth

  8. Planets Mercury Venus Mars Jupiter Saturn

  9. The Sun (a typical star)

  10. Stars

  11. Galaxies

  12. Clusters of Galaxies

  13. Stars nebulae molecular clouds star clusters Solar System black holes pulsars Sun planets moons comets meteors asteroids dust terrestrial jovian clusters and superclusters voids galaxies like the Milky Way quasars THE UNIVERSE What’s in the Universe? Big……………………………………..small

  14. What’s in the Universe? Alotof stuff !!! Scientific term: Mass

  15. Observation II: It is dark at night! • Big deal! • Indeed: it has cosmological consequences! • Let’s find out why!

  16. Night sky: No sun – just stars

  17. Look closer and find more dimmer stars

  18. If the Universe is infinite… There’s more and more… dimmer and dimmer stars

  19. Until finally…

  20. …the view fills up completely …and it’s as bright as the day!

  21. So, why is the night sky dark?(Olbers’ Paradox) • Conclusion: either • Universe isnot infinite or • Universe changesin time

  22. Observation III: Everything is moving away from us! • Measure spectrum of galaxies and compare to laboratory measurement • lines are shifted towards red • This is the Doppler effect: Red-shifted objects are moving away from us

  23. The Universe expands! • Where was the origin of the expansion? Everywhere! • Every galaxy sees the others receding from it – there is no center

  24. Conclusions from our Observations • The Universe has a finite age, so light from very distant galaxies has not had time to reach us, therefore the night sky is dark. • The universe expandsnow, so looking back in time it actually shrinks until…? Big Bang model: The universe is born out of a hot dense medium 13.7 billion years ago.

  25. How does the expansion work? • Like an explosion (hot, dense matter in the beginning), but space itselfexpands! • Slowed down by gravitational attraction • Attraction is the stronger, the more mass there is in the universe • Scientifically described by Einstein’s General theory of Relativity (1915)

  26. General Relativity ?! That’s easy! (Actually, it took Prof. Einstein 10 years to come up with that!) Rμν -1/2 gμνR = 8πG/c4 Tμν OK, fine, but what does that mean?

  27. The Idea behind General Relativity • In modern physics, we view space and time as a whole, we call it four-dimensional space-time. • Space-time is warped by the presence of masses like the sun, so “Mass tells space how to bend” • Objects (like planets) travel in “straight” lines through this curved space (we see this as orbits), so “Space tells matter how to move”

  28. Still too complicated? • Here is a picture: Sun Planet’s orbit

  29. Effects of General Relativity • Bending of starlight by the Sun's gravitational field (and other gravitational lensing effects)

  30. What General Relativity tells us • The more mass there is in the universe, the more “braking” of expansion there is • So the game is: Mass vs. Expansion And we can even calculate who wins!

  31. The Fate of the Universe – determined by a single number! • Critical density is the density required to just barely stop the expansion • We’ll use 0 = actual density/critical density: • 0 = 1 means it’s a tie • 0 > 1means the universe will recollapse (Big Crunch) Mass wins! • 0 < 1means gravity not strong enough to halt the expansion Expansion wins! • And the number is: 0 = 1

  32. The Shape of the Universe • In the basic scenario there is a simple relation between the density and the shape of space-time: DensityCurvature2-D exampleUniverseTime & Space 0>1 positive sphere closed, bound finite 0=1 zero (flat) plane open, marginal infinite 0<1 negative saddle open, unbound infinite

  33. The “size” of the Universe – depends on time! Expansion wins! It’s a tie! Mass wins! Time

  34. So, how much mass is in the Universe? • Can count all stars, galaxies etc. •  this gives the mass of all “bright” objects • But: there is also DARK MATTER

  35. “Bright” Matter • All normal or “bright” matter can be “seen” in some way • Stars emit light, or other forms of electromagnetic radiation • All macroscopic matter emits EM radiation characteristic for its temperature • Microscopic matter (particles) interact via the Standard Model forces and can be detected this way

  36. First evidence for dark matter: The missing mass problem • Showed up when measuring rotation curves of galaxies

  37. Is Dark Matter real? • It is real in the sense that it has specific properties • The universe as a whole and its parts behave differently when different amounts of the “dark stuff” is in it • Good news: it still behaves like mass, so Einstein’s cosmology still works!

  38. Properties of Dark Matter • Dark Matter is dark at all wavelengths, not just visible light • We can’t see it (can’t detect it) • Only effect is has: it acts gravitationally like an additional mass • Found in galaxies, galaxies clusters, large scale structure of the universe • Necessary to explain structure formation in the universe at large scales

  39. What is Dark Matter? • More precise: What does Dark matter consist of? • Brown dwarfs? • Black dwarfs? • Black holes? • Neutrinos? • Other exotic subatomic particles?

  40. Back to: Expansion of the Universe • Either it grows forever • Or it comes to a standstill • Or it falls back and collapses (“Big crunch”) • In any case: Expansion slows down! Surprise of the year 1998 (Birthday of Dark Energy): All wrong! It accelerates!

  41. Enter: The Cosmological Constant • Usually denoted 0, it represents a uniform pressure which either helps or retards the expansion (depending on its sign) • Physical origin of 0is unclear • Einstein’s biggest blunder – or not ! • Appears to be small but not quite zero! • Particle Physics’ biggest failure

  42. Effects of the “Cosmological Constant” • Introduced by Einstein, not necessary • Repulsive  accelerates expansion of universe Hard to distinguish today

  43. Triple evidence for Dark Energy • Supernova data • Large scale structure of the cosmos • Microwave background

  44. Microwave Background:Signal from the Big Bang • Heat from the Big Bang should still be around, although red-shifted by the subsequent expansion • Predicted to be a blackbody spectrum with a characteristic temperature of 2.725 Kelvin by George Gamow (1948) Cosmic Microwave Background Radiation (CMB)

  45. Discovery of Cosmic Microwave Background Radiation (CMB) • Penzias and Wilson (1964) • Tried to “debug” their horn antenna • Couldn’t get rid of “background noise”  Signal from Big Bang • Very, very isotropic (1 part in 100,000)

  46. CMB: Here’s how it looks like! Peak as expected from 3 Kelvin warm object Shape as expected from black body

  47. Latest Results: WMAP(Wilkinson Microwave Anisotropy Probe) • Measure fluctuations in microwave background • Expect typical size of fluctuation of one degree if universe is flat • Result: Universe is flat !

  48. Experiment and Theory Expect “accoustic peak” at l=200  There it is!

  49. Supernova Data • Type Ia Supernovae are • standard candles • Can calculate distance • from brightness • Can measure redshift • General relativity gives us distance as a • function of redshift for a given universe • Supernovae are further away than expected for any decelerating (“standard”) universe

  50. Supernova Data magnitude redshift

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