The Incredible Expanding Universe 8/6/09. Astronomy 101

Transcription

1 The Incredible Expanding Universe 8/6/09

2 Astronomy Picture of the Day

3 Outline for Today Astronomy Picture of the Day Return Lab 11 Q&A Session Distance Ladder Hubble's Law Dark Energy Minute Writing Break Lab 12 Hubble's Law

4 Questions for Today How are distances found in astronomy? What is the connection between distance and redshift? How is the size of the Universe changing over time? What is dark energy?

5 Distance Ladder Radar Ranging Redshift Supernova/Tully Fisher Cepheids Main Sequence Fitting Parallax Radar Ranging

6 Distance Ladder Parallax Redshift Supernova/Tully Fisher Cepheids Main Sequence Fitting Parallax Radar Ranging

7 Standard Candles Distance Ladder Main Sequence Fitting Redshift Supernova/Tully Fisher Cepheids Main Sequence Fitting Parallax Radar Ranging

8 Distance Ladder Standard Candles Cepheids Redshift Supernova/Tully Fisher Cepheids Main Sequence Fitting Parallax Radar Ranging

9 Distance Ladder Cepheids

10 Standard Candles Distance Ladder Supernova/Tully Fisher Redshift Supernova/Tully Fisher Cepheids Main Sequence Fitting Parallax Radar Ranging

11 Distance Ladder White Dwarf Supernova

12 Distance Ladder Tully Fisher Relationship

13 Distance Ladder Redshift Redshift Supernova/Tully Fisher Cepheids Main Sequence Fitting Parallax Radar Ranging

14 Suppose our estimates of distances of nearby Cepheids found through Main Sequence fitting are uncertain by 30%. Much more distant Cepheids measure in othe galaxies will have distance uncertainties that A) Increase with distance B) are at most 30% C) are at least 30% D) depend on the galaxy

15 Suppose our estimates of distances of nearby Cepheids found through Main Sequence fitting are uncertain by 30%. Much more distant Cepheids measure in othe galaxies will have distance uncertainties that A) Increase with distance B) are at most 30% C) are at least 30% D) depend on the galaxy

16 Almost All Galaxies are Moving Away From Us; Galaxies Far Away From Us Are Moving Faster Measure the redshift z -> derive the recessional velocity

17 Hubble s Original Data Velocity Distance

18 A More Recent Hubble Diagram Recessional velocity is proportional to distance. v = H D 0 H 0 is the Hubble Constant, units are km/s/mpc H 0 is the slope of this line

19 A galaxy s recessional velocity lets Measure v = c! you estimate its distance. z Then use: D = v/h 0

20 A galaxy appears to be receding at The galaxy s distance is probably closest to 7500 km/s A) 10 Mpc B) 50 Mpc C) 100 Mpc D) 1000 Mpc v = H D 0 H 0 = km/s/mpc

21 A galaxy appears to be receding at The galaxy s distance is probably closest to 7500 km/s A) 10 Mpc B) 50 Mpc C) 100 Mpc D) 1000 Mpc v = H D 0 H 0 = km/s/mpc

22 Redshifts Give Us Distances -> A 3-D Map Angular distribution of bright galaxies on the sky

23 The First Redshift Map Velocity (distance) You are here

24 Full Circle Redshift Map Fingers of God What could cause redshifts of galaxies? What sort of situation would cause this to happen?

25 Full Circle Redshift Map Fingers of God Fingers of God are artifacts. Produced by random motion of galaxies in clusters

26 The Sloan Digital Sky Survey (SDSS) -- has spectra for 675,000 galaxies!

27 What does the Hubble Law mean? v = H D 0

28 Cosmological Principal The universe looks about the same no matter where you are within it Matter is evenly distributed on very large scales in the universe No center & no edges Not proved but consistent with all observations to date (i.e. You are not special)

29 The Hubble Law implies that the entire Universe is expanding! v = H D 0 Occurs in every direction!

30 Velocity Away From Us Distance

31 The Cosmological Redshift Photons that travel for longer (from further away have experienced more expansion. Bigger Distance = Bigger Redshift Further seems Faster!

32 But if the Universe is expanding, won t the Solar System eventually expand apart? A) The Solar System may actually be shrinking now, which makes the Universe LOOK like it s expanding B) No, its gravity holds it together C) No, because there is no planetary redshift D) Eventually, but only after a very long time

33 But if the Universe is expanding, won t the Solar System eventually expand apart? It s not hard for other forces to be stronger than the push of expansion. None of these are expanding! They are bound together by electricity and/or gravity!

34 How does the expansion of the Universe effect our understanding of distance? Distances between faraway galaxies change while light travels distance? Astronomers think in terms of lookback time

35 Not An Explosion No Center No Edge Not Expanding Into Anything

36 Not An Explosion No Center No Edge Not Expanding Into Anything There was a beginning...

37 Your friend leaves your house. She later calls you on her cell phone, saying that she s been driving at 60 miles an hour directly away from you the whole time and is now 60 miles away. How long has A. 1 minute B. 30 minutes C. 60 minutes D. 120 minutes she been gone?

38 Your friend leaves your house. She later calls you on her cell phone, saying that she s been driving at 60 miles an hour directly away from you the whole time and is now 60 miles away. How long has A. 1 minute B. 30 minutes C. 60 minutes D. 120 minutes she been gone?

39 Your friend leaves your house. She later calls you on her cell phone, saying that she s been driving at 60 miles an hour directly away from you the whole time and is now 60 miles away. Distance from Your Home Time

40 Your friend leaves your house. She later calls you on her cell phone, saying that she s now driving at 60 miles an hour and was driving more slowly directly away from you the and is now 60 miles away. Distance from Your Home Time

41 Your friend leaves your house. She later calls you on her cell phone, saying that she s now driving at 60 miles an hour and was driving faster directly away from you the and is now 60 miles away. Distance from Your Home Time

42 You see a galaxy some distance away tha is retreating from you. When was the distance between it and you zero? Distance to the galaxy Time H 0 = km/s/mpc

43 You see a galaxy some distance away tha is retreating from you. When was the distance between it and you zero? Inverse of Hubble s Constant ~ Age of the Universe 1/H 0 ~ 14 Billion Years Distance to the galaxy Time H 0 = km/s/mpc

44 You see a galaxy some distance away tha is retreating from you. When was the distance between it and you zero? What if the Hubble constant was smaller i the past? Distance to the galaxy Time H 0 = km/s/mpc

45 You see a galaxy some distance away tha is retreating from you. When was the distance between it and you zero? What if the Hubble constant was greater in the past? Distance to the galaxy Time H 0 = km/s/mpc

46 What Force Could Slow the V Expansion? V Gravity Gravity Gravity Gravity

47 The exact age depends upon density Age of critical universe Age of closed universe

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49 If the Hubble Constant, H, is larger a great distances, then the A) Universe must be older than we suspect B) Matter in the Universe is not important to its motion C) Expansion is slowing D) All of the above

50 If the Hubble Constant, H, is larger a great distances, then the A) Universe must be older than we suspect B) Matter in the Universe is not important to its motion C) Expansion is slowing D) All of the above

51 The Problem... There are globular clusters older than the calculated age of the Universe

52 Type of universe determines distances to galaxies at a given redshift The point where any of the models intersects the pink line occurs at the same redshift Open universe Longer distance Dimmer! Closed universe Shorter distance Brighter!

53 Use Supernovas to Figure Out What Distance Equals What Redshift-> Find How H has Changed

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56 To Sum Up: A) The Universe is big B) The Universe is getting bigger C) The Universe is getting bigger faster

57 Minute Writing What are two questions you have on this lecture?

58 Assignments Read Chapter 23 Read Lab 13 News Article due next Tuesday Lab 12 due next Tuesday -- Reserve Time for This