A100 Exploring the Universe: Measuring the Universe. Martin D. Weinberg UMass Astronomy

Transcription

1 A100 Exploring the : Measuring the Martin D. Weinberg UMass Astronomy weinberg@astro.umass.edu November 18, 2014 Read: Chaps 20, 21 11/18/14 slide 1

2 Age of the in an Exam #2 scores posted in Mastering. See class web site for answer key. See TAs after class today for exams Read: Chaps 20, 21 11/18/14 slide 2

3 Age of the in an Exam #2 scores posted in Mastering. See class web site for answer key. See TAs after class today for exams Galaxies How did Hubble prove that galaxies lie far beyond the Milky Way? What is Law? How do distance measurements tell us the age of the? How does the universe s expansion affect our distance measurements? Read: Chaps 20, 21 11/18/14 slide 2

4 Age of the in an Exam #2 scores posted in Mastering. See class web site for answer key. See TAs after class today for exams Galaxies How did Hubble prove that galaxies lie far beyond the Milky Way? What is Law? How do distance measurements tell us the age of the? How does the universe s expansion affect our distance measurements? Your questions? Read: Chaps 20, 21 11/18/14 slide 2

5 to galaxies Read: Chaps 20, 21 11/18/14 slide 3

6 to galaxies The Distance Ladder Read: Chaps 20, 21 11/18/14 slide 3

7 relation Age of the in an Entire galaxies can also be used as standard candles because galaxy luminosity is related to rotation speed Read: Chaps 20, 21 11/18/14 slide 4

8 of astronomical distance measurements Age of the in an 1. Direct mesurements: Measuring the distance directly. Example: Radar Time of flight 2. Standard rulers: Size = Distance θ (angle on the sky). Need to know the true size of the object. Expanding supernova remnants 3. Standard candles: L apparent = L true /D 2. Need to know the true luminosity of an object. Main-sequence fitting Cepheid variables Read: Chaps 20, 21 11/18/14 slide 5

9 The Distance Ladder: Age of the in an We measure galaxy distances using a chain of interdependent techniques Read: Chaps 20, 21 11/18/14 slide 6

10 The Distance Ladder: Age of the in an The distance-measurement chain begins with parallax measurements that build on radar ranging in our solar system Using parallax and the relationship between luminosity, distance, and brightness, we can calibrate a series of standard candles We can measure distances greater than 10 billion light years using white dwarf supernovae as standard candles Read: Chaps 20, 21 11/18/14 slide 7

11 The Distance Ladder: Age of the in an The distance-measurement chain begins with parallax measurements that build on radar ranging in our solar system Using parallax and the relationship between luminosity, distance, and brightness, we can calibrate a series of standard candles We can measure distances greater than 10 billion light years using white dwarf supernovae as standard candles Read: Chaps 20, 21 11/18/14 slide 8

12 The Puzzle of Before Hubble, some scientists argued that spiral nebulae were entire galaxies like our Milky Way, while others maintained they were smaller collections of stars within the Milky Way The debate remained unsettled until someone finally measured their distances Read: Chaps 20, 21 11/18/14 slide 9

13 Physical nature of cloudy objects debated Rosse s sketch Lord Rosse (Irish nobleman) observed M51 with 72 inch mirror Read: Chaps 20, 21 11/18/14 slide 10

14 Physical nature of cloudy objects debated Artist s conception Lord Rosse (Irish nobleman) observed M51 with 72 inch mirror How it appeared to naked eye in early telescopes Read: Chaps 20, 21 11/18/14 slide 10

15 Physical nature of cloudy objects debated Hubble Space Telecope Lord Rosse (Irish nobleman) observed M51 with 72 inch mirror How it appeared to naked eye in early telescopes How it appears with the Hubble Space Telescope Read: Chaps 20, 21 11/18/14 slide 10

16 The Puzzle of Age of the in an Hubble settled the debate by measuring the distance to the Andromeda Galaxy using Cepheid variables as standard candles (late 1920 s... ) Read: Chaps 20, 21 11/18/14 slide 11

17 Law Age of the in an The spectral features of virtually all galaxies are redshifted... they are all moving away from us! Read: Chaps 20, 21 11/18/14 slide 12

18 Law Age of the in an The spectral features of virtually all galaxies are redshifted... they are all moving away from us! By measuring distances to galaxies, Hubble found that redshift and distance are related in a special way Read: Chaps 20, 21 11/18/14 slide 12

19 Age of the in an Edwin Hubble (1929) measured distances to 25 galaxies Distances from Cepheid variables Velocities from redshift of spectral lines: v = c z = cz z = v c = λ λ 0 λ 0 = λ λ 0 He found: recession velocity increases linearly with distance! Read: Chaps 20, 21 11/18/14 slide 13

20 Age of the in an How to really do it... Read: Chaps 20, 21 11/18/14 slide 14

21 Age of the in an How to really do it... Spectra of cooler stars show very strong absorption lines due to singly-ionized calcium: Read: Chaps 20, 21 11/18/14 slide 14

22 Age of the in an How to really do it... Spectra of cooler stars show very strong absorption lines due to singly-ionized calcium: These strong absoption line stand out in the spectrum! H K Read: Chaps 20, 21 11/18/14 slide 14

23 Age of the in an Read: Chaps 20, 21 11/18/14 slide 15

24 Age of the in an Read: Chaps 20, 21 11/18/14 slide 15

25 Age of the in an Example: v = H o d H o = 70 km/s/mpc New distance indicator: d = zc/h o Redshift of a galaxy is z = 0.1 Recession velocity: v = zc = 30,000 km/s Distance: d = zc H o = 30,000 km/s 70 km/s/mpc = 429 Mpc Read: Chaps 20, 21 11/18/14 slide 15

26 Law Age of the in an Law: velocity = H 0 distance Read: Chaps 20, 21 11/18/14 slide 16

27 Law Redshift of a galaxy tells us its distance through Law: distance = velocity H 0 = zc H 0 Read: Chaps 20, 21 11/18/14 slide 17

28 Law Age of the in an Hubble Ultra Deep Field Distances of farthest galaxies are measured from redshifts Read: Chaps 20, 21 11/18/14 slide 18

29 Age of the Age of the in an How do distance measurements tell us the age of the? Read: Chaps 20, 21 11/18/14 slide 19

30 Age of the in an 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 she been gone? (A) 1 minute (B) 30 minutes (C) 60 minutes (D) 120 minutes Read: Chaps 20, 21 11/18/14 slide 20

31 Age of the in an 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 she been gone? (A) 1 minute (B) 30 minutes (C) 60 minutes (D) 120 minutes Read: Chaps 20, 21 11/18/14 slide 20

32 Age of the in an Observations suggest: 1. The expansion rate appears to be the same everywhere! 2. The has no center and no boundary! (as far as we can tell) Read: Chaps 20, 21 11/18/14 slide 21

33 Age of the in an One example of something that expands but has no center or edge is the surface of a balloon Read: Chaps 20, 21 11/18/14 slide 22

34 The Age of the in an The looks about the same no matter where you are within it Matter is evenly distributed on very large scales in the There is NO center and no edges Not proved but consistent with all observations to date Read: Chaps 20, 21 11/18/14 slide 23

35 Age of the in an Philosphically consistent with the lessons learned from Ptolemy to Copernicus We don t want to make the same mistake again! Read: Chaps 20, 21 11/18/14 slide 24

36 Age of the in an Philosphically consistent with the lessons learned from Ptolemy to Copernicus We don t want to make the same mistake again! Copernican view: nothing special about Earth s position in the Read: Chaps 20, 21 11/18/14 slide 24

37 Age of the in an Philosphically consistent with the lessons learned from Ptolemy to Copernicus We don t want to make the same mistake again! Copernican view: nothing special about Earth s position in the This is often called the Copernican Read: Chaps 20, 21 11/18/14 slide 24

38 The Age of the in an Observations support the idea that the is both isotropic and homogeneous Homogeneous: At large scales, the looks the same everywhere There is no preferred location I.e. no center Isotropic: At large scales, the looks the same in all directions on the sky There is no special direction I.e. no axis Read: Chaps 20, 21 11/18/14 slide 25

39 The Age of the in an Homogeneous looks the same independent of location Isotropic looks the same independent of direction In 3 dimensions In 2 dimensions Read: Chaps 20, 21 11/18/14 slide 26

40 The Age of the in an Isotropy and homogeneity are related: Isotropy + Copernican Isotropy + Isotropy around another point = Homogeneity = Homogeneity Read: Chaps 20, 21 11/18/14 slide 27

41 The Age of the in an The universe is homogeneous and isotropic when viewed on a large enough scale. The derives from the Copernican But not demanded by any physical model It can not be proven in a mathematical sense However: Supported by numerous observations Great weight from purely empirical grounds Read: Chaps 20, 21 11/18/14 slide 28

42 The : Newton s version Age of the in an To prevent one part of the from collapsing (i.e. into a black hole) Homogeneous Isotropic Infinite in size No center Infinite in time (i.e. no beginning or end of time) Always has been Always will be Read: Chaps 20, 21 11/18/14 slide 29

43 The : Newton s version Age of the in an To prevent one part of the from collapsing (i.e. into a black hole) Homogeneous Isotropic Infinite in size No center Infinite in time (i.e. no beginning or end of time) Always has been Always will be Known as the Perfect cosmological principle. Inconsistent with expansion! Read: Chaps 20, 21 11/18/14 slide 29

44 Age of the in an What is the expanding into? (A) Nothingness (B) Extra dimensions of space and time (C) The is not really expanding, it is stretching Read: Chaps 20, 21 11/18/14 slide 30

45 Age of the in an What is the expanding into? (A) Nothingness (B) Extra dimensions of space and time (C) The is not really expanding, it is stretching Read: Chaps 20, 21 11/18/14 slide 30

46 Age of the What is expanding? in an The spaces between faraway galaxies stretch What is not expanding or stretching Read: Chaps 20, 21 11/18/14 slide 31

47 Age of the What is expanding? in an The spaces between faraway galaxies stretch What is not expanding or stretching You and I are not expanding The Earth is not expanding The Sun isn t expanding The entire Milky Way galaxy is not expanding Read: Chaps 20, 21 11/18/14 slide 31

48 Age of the What is expanding? in an The spaces between faraway galaxies stretch What is not expanding or stretching On small scales, the effect of the s stretching is completely overwhelmed by other forces Read: Chaps 20, 21 11/18/14 slide 31

49 Age of the What is expanding? in an The spaces between faraway galaxies stretch What is not expanding or stretching On small scales, the effect of the s stretching is completely overwhelmed by other forces The atomic forces which hold people s bodies together The Earth s gravity The Sun s gravity The Galaxy s gravity Read: Chaps 20, 21 11/18/14 slide 31

50 Age of the What is expanding? in an The spaces between faraway galaxies stretch What is not expanding or stretching On small scales, the effect of the s stretching is completely overwhelmed by other forces On very large scales, the effect of the universe s stretching becomes noticeable above the effects of local gravity and other forces which tend to hold things together Read: Chaps 20, 21 11/18/14 slide 31

51 Age of the What is expanding? in an The spaces between faraway galaxies stretch What is not expanding or stretching On small scales, the effect of the s stretching is completely overwhelmed by other forces On very large scales, the effect of the universe s stretching becomes noticeable above the effects of local gravity and other forces which tend to hold things together This is often called the Hubble Flow Read: Chaps 20, 21 11/18/14 slide 31

52 Age of the in an You observe a galaxy moving away from you at 0.1 light-years per year, and it is now 1.4 billion light-years away from you. How long has it taken to get there? (A) 1 million years (B) 14 million years (C) 10 billion years (D) 14 billion years Read: Chaps 20, 21 11/18/14 slide 32

53 Age of the in an You observe a galaxy moving away from you at 0.1 light-years per year, and it is now 1.4 billion light-years away from you. How long has it taken to get there? (A) 1 million years (B) 14 million years (C) 10 billion years (D) 14 billion years Read: Chaps 20, 21 11/18/14 slide 32

54 Age of the in an You observe a galaxy moving away from you at 0.1 light-years per year, and it is now 1.4 billion light-years away from you. How long has it taken to get there? (A) 1 million years (B) 14 million years (C) 10 billion years (D) 14 billion years constant tells us age of universe because it relates velocities and distances of all galaxies: Age = Distance Velocity 1 H 0 Read: Chaps 20, 21 11/18/14 slide 32

55 in an Age of the in an expanding universe How does the s expansion affect our distance measurements? Read: Chaps 20, 21 11/18/14 slide 33

56 in an Age of the in an expanding universe How does the s expansion affect our distance measurements? Distances between faraway galaxies change while light travels Read: Chaps 20, 21 11/18/14 slide 33

57 in an Age of the in an expanding universe How does the s expansion affect our distance measurements? Distances between faraway galaxies change while light travels Astronomers think in terms of lookback time rather than distance Read: Chaps 20, 21 11/18/14 slide 33

58 in an Age of the in an expanding universe Expansion stretches photon wavelengths, causing a cosmological redshift directly related to lookback time Read: Chaps 20, 21 11/18/14 slide 34

59 Age of the in an How did Hubble prove that galaxies lie far beyond the Milky Way? He measured the distance to the Andromeda galaxy using Cepheid variable stars as standard candles What is Law? The faster a galaxy is moving away from us, the greater its distance: velocity = H 0 distance Read: Chaps 20, 21 11/18/14 slide 35

60 How do we observe the life histories of galaxies? Age of the in an Observing galaxies at different distances shows how they age Read: Chaps 20, 21 11/18/14 slide 36

61 Age of the in an Deep observations show us very distant galaxies as they were much earlier in time (Old light from young galaxies) Read: Chaps 20, 21 11/18/14 slide 37