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Discovering galaxies���Bursting through the limits of space and time
Jean-René Roy Space Telescope Science Institute
Hubble Science Briefing
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
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How were galaxies discovered?
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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)
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The Herschels - William (1738-1822), Caroline (1750-1848) & John (1792-1871)
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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”
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.... 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
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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)
“Island Universes”
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William Parsons, 3rd Earl of Rosse (1800-1867)
Birr Castle, Ireland
72-inch Leviathan
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Whirlpool Galaxy (M51 or NGC 5194/95)
Leviathan HST
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How far away? ���How we found out
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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
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Isaac Roberts introduces astrophotography for nebular work
1829-1904
Roberts took this first photograph of the Andromeda galaxy on December 29, 1888
Roberts observatory, Crowborough - Sussex
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New technologies: sturdy metal mount, precision motor drive, glass mirror 18
Shapley: The Milky Way is big (300,000 l-y) and is everything = the universe, but ...
Harlow Shapley (1885-1972)
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Novae!
~24 novae/yr are observed every year in the Andromeda galaxy
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Knut Lundmark (1889-1958) Heber Curtis (1872-1942)
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)
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Ernst Öpik (1893-1985) In 1922, Ernst Öpik uses stellar orbital velocity and starlight density
of Andromeda:
Distance = 1,440,000 l-y Mass = 4.5 billions “suns”
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“Cracking the nut” ���of galaxies
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Text
Henrietta Leavitt and a new class of
variable stars: Cepheids
1868-1921
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N not a nova it is a
variable Cepheid
Andromeda Galaxy, M31 by Edwin Hubble
Edwin Hubble (1889-1953)
“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 1st Jan 1925 “Cepheids in Spiral Nebulae”, Edwin Hubble
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... there is the shadow of ���Adriaan van Maanen
1894-1946
M 33 28
Edwin Hubble
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How was the expansion of the universe found?
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The expanding universe
Albert Einstein (1879-1955)
Text
General Relativity: A theory of space-time and gravitation 31
Alexander Friedman (1888-1925)
Georges Lemaître (1894-1966)
Slipher Humason Hubble
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Lundmark (1889-1958)
1924: First “distance-velocity diagram” by Knut Lundmark
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Edwin Hubble
Milton Humason
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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
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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.”
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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
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The universe was condensed in a “fireball” of space-time 13.7 billion years ago
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Georges Lemaître
40 rue de Namur Louvain
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Hubble Deep Fields
Galaxy cluster Abell 2744 ~3.5 Giga-ly
More distant field
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The world of galaxies is much more varied and strange than inferred by Hubble’s elegant scheme.
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Movie Credits: Frank Summers (STScI), Chris Mihos (Case Western Reserve Univ.) & Lars Hernquist (Harvard) �
Download movie here: http://hubblesite.org/newscenter/archive/releases/2008/16/
video/d/
“Cosmic Collisions” A Computer Simulation of Galaxies Colliding
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Adam Riess
Brian Schmidt
Albert Einstein Saul Perlmutter
Signatures of dark energy and of dark matter
2011 Physics Nobel
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In the last 100 years, ���the volume of the observed universe has been multiplied
by ���1015 times, or ���
“one million billion times !”
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200 billion galaxies in the observable universe, each with
about 100 billion stars like the sun
20,000,000,000,000,000,000,000 stars
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The Suomi NPP Blue Marble, Credit:NASA/NOAA
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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
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Acknowledgments
• Zoltan Levay, STScI
• Carolyn Slivinski, STScI
• Frank Summers, STScI
• Paul Espinoza, JHU Peabody Library
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Thank you 58
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