Hubble Science Briefing Discovering galaxies Bursting through the

Hubble Science Briefing Discovering galaxies Bursting through the limits of space and time Jean-René Roy Space Telescope Science Institute 5 July, 2012

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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 humankind curiosity, astuteness and ingenuity 3

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How were galaxies discovered? 6

Pre-history Al-Sufi (903 -986) • • 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 7

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

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

. . 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

“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

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

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Leviathan HST Whirlpool Galaxy (M 51 or NGC 5194/95) 14

How far away? How we found out 15

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

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

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

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

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

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

Vesto Slipher (1875 -1969) 22

In 1922, Ernst Öpik uses stellar orbital velocity and starlight density of Andromeda: Ernst Öpik (1893 -1985) Distance = 1, 440, 000 l-y Mass = 4. 5 billions “suns” 23

“Cracking the nut” of galaxies 24

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

N not a nova it is a variable Cepheid Edwin Hubble (1889 -1953) Andromeda Galaxy, M 31 by Edwin Hubble “The spiral is 7. 25 times as far away as the Cloud, or about 680, 000 l-y. ” 26

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

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

Edwin Hubble 29

How was the expansion of the universe found? 30

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

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

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

Milton Humason Edwin Hubble 34

The “Hubble law” of 1929 v = H 0 d v = recessional velocity H 0 = Hubble constant d = distance H 0 = 72 km/sec per megaparsec or 20 km/sec per million light-years 35

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

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

The universe was condensed in a “fireball” of space-time 13. 7 billion years ago 38

Georges Lemaître 40 rue de Namur Louvain 39

Hubble Deep Fields More distant field Galaxy cluster Abell 2744 ~3. 5 Giga-ly 40

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

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

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

In the last 100 years, the volume of the observed universe has been multiplied by 15 10 times, or “one million billion times !” 46

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200 billion galaxies in the observable universe, each with about 100 billion stars like the sun 20, 000, 000, 000 stars 51

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54 The Suomi NPP Blue Marble, Credit: NASA/NOAA

Discovering galaxies: some references • • • The Realm of the Nebulae, Edwin Hubble, Yale University Press, 1936 Man Discovers the Galaxies, R. Berendzen, Richard Hart & Daniel Seeley, Science History Publications, 1976 The Day We Found the Universe, Marcia Bartusiak, Pantheon Books, 2009 Discovering the Expanding Universe, H. Nussbaumer & L. Bieri, Cambridge University Press, 2009 http: //en. wikipedia. org/wiki/Galaxy 55

Images from • • • NASA and ESA Space Telescope Science Institute Gemini Observatory Canada France Hawaii Telescope Peabody Library, Johns Hopkins University Wikipedia Commons 56

Acknowledgments • • Zoltan Levay, STSc. I Carolyn Slivinski, STSc. I Frank Summers, STSc. I Paul Espinoza, JHU Peabody Library 57

Thank you 58