ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies � NNOUNCEMENTS � NNOUNCEMENTS • Alternate final date Alternate final date : Monday, Dec 7, 5:30-8pm. • Next observing night: Mon, Nov. 16, 7pm • Homework #7 due on Tuesday 11/10, by 5pm
Mapping the Universe: We Mapping the Universe: We REVIEW need Distances to Galaxies! need Distances to Galaxies! The problem: or Methods we are familiar with: Radar and Stellar parallax Stellar parallax Radar Only useful inside the Solar System System A few thousand ly ly Only useful inside the Solar A few thousand
DISTANCE DISTANCE REVIEW Main-Sequence Fitting Main-Sequence Fitting ESTIMATE 1 ESTIMATE 1 • Start with cluster Start with cluster A A • (upper) whose whose (upper) distance known via distance known via A A parallax parallax • Compare with other Compare with other • B B cluster B (lower) B (lower) cluster • Get Get distance to B distance to B • from brightness from brightness difference difference Distances up to ~1 million ~1 million light years Distances up to light years
DISTANCE DISTANCE Cepheid variable stars Cepheid variable stars REVIEW ESTIMATE 2 ESTIMATE 2 Period - Period - Luminosity Luminosity relation relation brighter Cepheids Cepheids brighter have longer periods have longer periods
DISTANCE DISTANCE Tully-Fisher Relation Tully-Fisher Relation REVIEW ESTIMATE 3 ESTIMATE 3 • Fast rotation speeds in • Fast rotation speeds in spiral galaxies spiral galaxies � more mass in galaxy more mass in galaxy � � higher luminosity higher luminosity � Measure rotation speeds rotation speeds Measure to infer luminosity luminosity to infer Need bright “ “edge-on edge-on” ” Need bright spirals, estimate tilt spirals, estimate tilt Distances up to ~1 billion ly ly Distances up to ~1 billion
Even brighter: DISTANCE Even brighter: DISTANCE REVIEW ESTIMATE 4 ESTIMATE 4 White dwarf supernovae White dwarf supernovae • Nearly the Nearly the same same • amount of energy of energy amount released every released every time. time. why? why? • “ “Standard Standard • explosion” ” = = explosion fusion of 1.4 solar fusion of 1.4 solar masses of masses of material material
Summary Summary REVIEW “Distance Ladder Distance Ladder” ” to measure universe to measure universe “ Different standard candles are useful Different standard candles are useful for different distances for different distances
Distance measurements allowed to allowed to Distance measurements make a a MAJOR MAJOR discovery about our discovery about our make Universe Universe • Before 1924, “spiral nebulae” were thought to be small and located inside the Milky Way
Andromeda found to be far outside outside Milky Way! Milky Way! Andromeda found to be far • Edwin Hubble Edwin Hubble in 1924 in 1924 • identified Cepheids Cepheids in in identified Andromeda (M33) � Andromeda (M33) � showed they were far far showed they were outside of Milky Way! of Milky Way! outside – “ “Island Universes Island Universes” ” – • His first big discovery! His first big discovery! • • But then he turned his But then he turned his • attention to OTHER OTHER attention to galaxies galaxies Hubble using new Hubble using new 100” ” Hooker telescope Hooker telescope 100 at Mt. Wilson (above LA) at Mt. Wilson (above LA)
Hubble’ ’s s observations showed a observations showed a very very Hubble startling result about the result about the universe. universe. startling • Vesto Slipher Vesto Slipher (1912) reported that most (1912) reported that most • galaxies showed Doppler redshifts redshifts galaxies showed Doppler • Edwin Hubble Edwin Hubble, using new 100 , using new 100” ” telescope, telescope, • started busily measuring galaxy redshifts redshifts started busily measuring galaxy • Hubble Hubble (1929) announced that (1929) announced that redshifts redshifts of of • galaxies appear to appear to increase with distance increase with distance galaxies from us from us • This was startling: Suggested an This was startling: Suggested an • EXPANDING UNIVERSE ! ! EXPANDING UNIVERSE
“Hubble Hubble’ ’s Law s Law” ” “ v = H o � d Velocity of Hubble’s Distance Recession Constant (Doppler Shift) (km/sec) (km/sec/Mpc) (Mpc) velocity velocity Best current Best current values for values for expansion expansion H o = 71 71+ +/- 4 /- 4 H o = distance distance km/s/Mpc km/s/Mpc
Hubble Space Telescope was Hubble Space Telescope was designed to accurately measure accurately measure designed to the Hubble constant the Hubble constant • High resolution images to find faint Cepheid variable stars in very distant galaxies
Clicker Question Clicker Question What is Hubble’ ’s Law? s Law? What is Hubble A. An idea stating that more distant galaxies move move A. An idea stating that more distant galaxies away from us faster than closer ones than closer ones away from us faster B. An equation giving the maximum luminosity for a B. An equation giving the maximum luminosity for a white dwarf supernova white dwarf supernova C. The relationship between the period and The relationship between the period and C. luminosity of a Cepheid luminosity of a Cepheid variable star. variable star. D. The The law giving the maximum speed that a law giving the maximum speed that a D. galaxy can move at. galaxy can move at. E. The idea that there are more galaxies outside E. The idea that there are more galaxies outside our own and that the universe contains immense our own and that the universe contains immense numbers of these “ “island universes. island universes.” ” numbers of these
Clicker Question Clicker Question What is Hubble’ ’s Law? s Law? What is Hubble A. An idea stating that more distant galaxies move move A. An idea stating that more distant galaxies away from us faster than closer ones than closer ones away from us faster B. An equation giving the maximum luminosity for a B. An equation giving the maximum luminosity for a white dwarf supernova white dwarf supernova C. The relationship between the period and The relationship between the period and C. luminosity of a Cepheid luminosity of a Cepheid variable star. variable star. D. The The law giving the maximum speed that a law giving the maximum speed that a D. galaxy can move at. galaxy can move at. E. The idea that there are more galaxies outside E. The idea that there are more galaxies outside our own and that the universe contains immense our own and that the universe contains immense numbers of these “ “island universes. island universes.” ” numbers of these
Balloon analogy for Balloon analogy for expanding universe expanding universe • Each dot on the Each dot on the • balloon can be balloon can be thought of as a thought of as a galaxy. galaxy. As the balloon As the balloon expands, galaxies expands, galaxies move farther away move farther away from each other from each other
Clicker Question Clicker Question What are the velocities of B, C and D What are the velocities of B, C and D as measured by A? as measured by A? A. B: 1 cm/s; C: 2 cm/s; D: 3 B: 1 cm/s; C: 2 cm/s; D: 3 cm/s cm/s A. B. B: 3 cm/s; C: 1cm/s; D: B: 3 cm/s; C: 1cm/s; D: 2 2 cm/s cm/s B. C. B: 2 cm/s; C: 4 cm/s; D: B: 2 cm/s; C: 4 cm/s; D: 6 6 cm/s cm/s C. D. B: 1cm/s; C: 3 cm/s; D: B: 1cm/s; C: 3 cm/s; D: 6 6 cm/s cm/s D.
Clicker Question Clicker Question What are the velocities of B, C and D What are the velocities of B, C and D as measured by A? as measured by A? A. B: 1 cm/s; C: 2 cm/s; D: 3 B: 1 cm/s; C: 2 cm/s; D: 3 cm/s cm/s A. B. B: 3 cm/s; C: 1cm/s; D: B: 3 cm/s; C: 1cm/s; D: 2 2 cm/s cm/s B. C. B: 2 cm/s; C: 4 cm/s; D: B: 2 cm/s; C: 4 cm/s; D: 6 6 cm/s cm/s C. D. B: 1cm/s; C: 3 cm/s; D: B: 1cm/s; C: 3 cm/s; D: 6 6 cm/s cm/s D.
Balloon analogy for Balloon analogy for expanding universe expanding universe • On an expanding On an expanding • balloon, no galaxy is balloon, no galaxy is at the “ “center center” ” of of at the expansion; no edge expansion; no edge • Expansion happens Expansion happens • into a higher into a higher dimension (2-D (2-D dimension surface into a 3-D surface into a 3-D space) space) • Is our 3-D space Is our 3-D space • expanding through a expanding through a 4 th th dimension? dimension? 4
A Better Way To Image the A Better Way To Image the Expanding Universe Expanding Universe • NOT NOT like an explosion of galaxies • THROUGH space from a center place THROUGH • The space BETWEEN BETWEEN galaxies is expanding, carrying the galaxies away expanding from each other – Why don’t galaxies themselves expand? Gravity!
Clicker Question Clicker Question No matter which direction we look, we see No matter which direction we look, we see galaxies moving away from us. Therefore, we galaxies moving away from us. Therefore, we must be at the center of the expansion. must be at the center of the expansion. A. True True A. B. False False B.
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