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Discovering galaxies Bursting through the limits of space and time

Hubble Science Briefing. Discovering galaxies Bursting through the limits of space and time. Jean-René Roy Space Telescope Science Institute. 5 July, 2012. 2. The key ideas. Many people “ discovered ” galaxies Many people found the distances to galaxies

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Discovering galaxies Bursting through the limits of space and time

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  1. Hubble Science Briefing Discovering galaxiesBursting through the limits of space and time • Jean-René Roy • Space Telescope Science Institute 5 July, 2012

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  3. The key ideas • Many people “discovered” galaxies • Many people found the distances to galaxies • A few people found that the universe was expanding and accelerating • Establishing priority is a complex exercise • The discovery of the “sidereal universe” is a fascinating story of humankindcuriosity, astuteness and ingenuity 3

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  6. How were galaxies discovered? 6

  7. Pre-history • Abd al-Rahman ibn Umar al-Sufi (903 - 986) refers to a “small cloud” in Andromeda • Book of the constellations of the fixed stars in year 964 Al-Sufi (903-986) 7

  8. The Herschels - William (1738-1822), Caroline (1750-1848) & John (1792-1871) 8

  9. While William Herschel is surveying the sky for binary stars, his sister searches for new comets. With her comet finder, Caroline discovers several new “nebulae” William switches his program to the “study of the sidereal Universe” 9

  10. .... the naked eye, which, as we have before estimated, can only see the stars of the seventh magnitude so as to distinguish them; but it is nevertheless very evident that the united lustre of millions of stars, such as I suppose the nebula in Andromeda to be, will reach our sight in the shape of a very small, faint nebulosity; since the nebula which I speak may easily be seen in a fine evening. William Herschel, Construction of the Heavens, 1785 10

  11. “Island Universes” Immanuel Kant 1724 - 1804 “I easily persuaded myself that these stars can be nothing else than a mass of many fixed stars... On account of their feeble light, they are removed to an inconceivable distance from us.” (1755) 11

  12. (1800-1867) William Parsons, 3rd Earl of Rosse 72-inch Leviathan Birr Castle, Ireland 12

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  14. HST Leviathan Whirlpool Galaxy (M51 or NGC 5194/95) 14

  15. How far away? How we found out 15

  16. Extragalactic Renaissance • Opinions change dramatically between 1900 and 1920 • Opposing views for “in” (Shapley/van Maanen) and for “out” (Curtis, Lundmark, Öpik, Hubble) • Strong observational evidence builds up quickly for most nebulae to be “extragalactic” • Several new technologies provide the key tools 16

  17. Isaac Roberts introduces astrophotography for nebular work Roberts observatory, Crowborough - Sussex 1829-1904 Roberts took this first photograph of the Andromeda galaxy on December 29, 1888 17

  18. New technologies: sturdy metal mount, precision motor drive, glass mirror 18

  19. Harlow Shapley (1885-1972) Shapley: The Milky Way is big (300,000 l-y) and is everything = the universe, but ... 19

  20. Novae! ~24 novae/yr are observed every year in the Andromeda galaxy 20

  21. Heber Curtis (1872-1942) Knut Lundmark (1889-1958) In 1917, novae in the Andromeda “nebula”: they are located at 650,000 light-years = well outside the Milky Way 21

  22. Vesto Slipher (1875-1969) 22

  23. In 1922, Ernst Öpik uses stellar orbital velocity and starlight density of Andromeda: Distance = 1,440,000 l-y Mass = 4.5 billions “suns” Ernst Öpik (1893-1985) 23

  24. “Cracking the nut”of galaxies 24

  25. Henrietta Leavitt and a new class of variable stars: Cepheids 1868-1921 Text 25

  26. N not a nova it is a variable Cepheid Edwin Hubble (1889-1953) Andromeda Galaxy, M31 by Edwin Hubble “The spiral is 7.25 times as far away as the Cloud, or about 680,000 l-y.” 26

  27. Corcoran Hall, George Washington University, DC American Astronomical Society 1st Jan 1925 “Cepheids in Spiral Nebulae”, Edwin Hubble 27

  28. ... there is the shadow of Adriaan van Maanen 1894-1946 M 33 28

  29. Edwin Hubble 29

  30. How was the expansion of the universe found? 30

  31. The expanding universe Text Albert Einstein (1879-1955) General Relativity: A theory of space-time and gravitation 31

  32. Georges Lemaître (1894-1966) Slipher Humason Hubble Alexander Friedman (1888-1925) 32

  33. 1924: First “distance-velocity diagram” by Knut Lundmark Lundmark (1889-1958) 33

  34. Milton Humason Edwin Hubble 34

  35. The “Hubble law” of 1929 v = H0 d v = recessional velocity H0 = Hubble constant d = distance H0 = 72 km/sec per megaparsec or 20 km/sec per million light-years 35

  36. H. Nussbaumer and L. Bieri (2011) write that Hubble was very dubious that the recessional velocities represented the expansion of the universe: “Actually Hubble never believed in such a thing.” 36

  37. The evolving universe As we go back into the early history of the universe, we see a different universe • Stars are forming at a much higher rate • This rate is changing rapidly over the first Gyrs (1 Gyr = 109 years) • Galaxies are merging at a higher rate • Galaxy morphology is different 37

  38. The universe was condensed in a “fireball” of space-time 13.7 billion years ago 38

  39. Georges Lemaître 40 rue de Namur Louvain 39

  40. Hubble Deep Fields More distant field Galaxy cluster Abell 2744 ~3.5 Giga-ly 40

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  42. The world of galaxies is much more varied and strange than inferred by Hubble’s elegant scheme. 42

  43. “Cosmic Collisions” A Computer Simulation of Galaxies Colliding Download movie here: http://hubblesite.org/newscenter/archive/releases/2008/16/video/d/ 43 Movie Credits: Frank Summers (STScI), Chris Mihos (Case Western Reserve Univ.) & Lars Hernquist (Harvard)

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  45. 2011 Physics Nobel Adam Riess Brian Schmidt Albert Einstein Saul Perlmutter Signatures of dark energy and of dark matter 45

  46. In the last 100 years, the volume of the observed universe has been multiplied by 1015 times, or “one million billion times !” 46

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