Editing Dark matter (section)

=== Early history ===
The hypothesis of dark matter has an elaborate history.<ref name=GianfracoHooperHistory/><ref>{{cite journal |last1=de Swart |first1=J.G. |last2=Bertone |first2=G. |last3=van Dongen |first3=J. |year=2017 |title=How dark matter came to matter |journal=[[Nature Astronomy]] |volume=1 |issue=59 |page=59 |arxiv=1703.00013 |bibcode=2017NatAs...1E..59D |doi=10.1038/s41550-017-0059 |s2cid=119092226 }}</ref>
[[William Thomson, 1st Baron Kelvin|Wm. Thomson, Lord Kelvin]], discussed the potential number of stars around the Sun in the appendices of a book based on a series of lectures given in 1884 in Baltimore.<ref name=Kelvin-1904/><ref name=GianfracoHooperHistory/> He inferred their density using the observed velocity dispersion of the stars near the Sun, assuming that the Sun was 20–100&nbsp;million years old. He posed what would happen if there were a thousand million stars within 1&nbsp;[[parsec|kiloparsec]] of the Sun (at which distance their parallax would be 1&nbsp;[[minute and second of arc|milli-arcsecond]]). Kelvin concluded
<blockquote>Many of our supposed thousand million stars – perhaps a great majority of them – may be dark bodies.<ref name=Kelvin-1904>{{cite book |last=Thompson |first=((W., Lord Kelvin)) |author-link=William Thomson, 1st Baron Kelvin |year=1904 |title=Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light |publisher=C.J. Clay and Sons |place=London, UK |page=274 |url=https://babel.hathitrust.org/cgi/pt?id=ien.35556038198842&view=1up&seq=304 |via=hathitrust.org }}</ref><ref name=ArsTech-2017-02-03>{{cite magazine |title=A history of dark matter  |date=2017-02-03 |df=dmy-all |magazine=[[Ars Technica]] |url=https://arstechnica.com/science/2017/02/a-history-of-dark-matter/ |access-date=8 February 2017 |lang=en-us}}</ref></blockquote>

In 1906, [[Henri Poincaré]]<ref name=Poincaré-1906/> used the [[French language|French]] term [{{Lang|fr|matière obscure}}] ("dark matter") in discussing Kelvin's work.<ref name=Poincaré-1906>{{cite journal |last1=Poincaré |first1=H. |author-link=Henri Poincaré |year=1906 |title=La Voie lactée et la théorie des gaz |journal=Bulletin de la Société astronomique de France |volume=20 |pages=153–165 |url=https://babel.hathitrust.org/cgi/pt?id=uiug.30112110949630&view=1up&seq=171 |trans-title=The Milky Way and the theory of gases |language=fr}}</ref><ref name=ArsTech-2017-02-03/> He found that the amount of dark matter would need to be less than that of visible matter, incorrectly, it turns out.<ref name=ArsTech-2017-02-03/><ref name=GianfracoHooperHistory/>

The second to suggest the existence of dark matter using stellar velocities was Dutch astronomer [[Jacobus Kapteyn]] in 1922.<ref>{{cite journal |first=J.C. |last=Kapteyn |author-link=Jacobus Kapteyn |year=1922 |title=First attempt at a theory of the arrangement and motion of the sidereal system |journal=Astrophysical Journal |volume=55 |pages=302–327 |bibcode=1922ApJ....55..302K |doi=10.1086/142670 |quote=It is incidentally suggested when the theory is perfected it may be possible to determine ''the amount of dark matter'' from its gravitational effect. {{grey|[''emphasis in original'']}} }}</ref><ref name=Patras2014>{{cite conference |last=Rosenberg |first=Leslie J. |date=30 June 2014 |title=Status of the Axion Dark-Matter Experiment (ADMX) |conference=10th PATRAS Workshop on Axions, WIMPs and WISPs |page=2 |url=http://indico.cern.ch/event/300768/session/0/contribution/30/attachments/566901/780884/Rosenberg-Patras_30jun14.pdf |url-status=live |archive-url=https://web.archive.org/web/20160205163816/http://indico.cern.ch/event/300768/session/0/contribution/30/attachments/566901/780884/Rosenberg-Patras_30jun14.pdf |archive-date=2016-02-05 |conference-url=http://axion-wimp2014.desy.de }}</ref>

A publication from 1930 by Swedish astronomer [[Knut Lundmark]] points to him being the first to realise that the universe must contain much more mass than can be observed.<ref>{{cite journal |last=Lundmark |first=K. |author-link=Knut Lundmark |date=1930-01-01 |title=Über die Bestimmung der Entfernungen, Dimensionen, Massen, und Dichtigkeit fur die nächstgelegenen anagalacktischen Sternsysteme |lang=de |trans-title=On determination of distances, dimensions, masses, and densities for the nearest non-galactic star systems |journal=Meddelanden Fran Lunds Astronomiska Observatorium |volume=125 |pages=1–13 |bibcode=1930MeLuF.125....1L  |url=https://ui.adsabs.harvard.edu/abs/1930MeLuF.125....1L }}</ref> Dutch radio astronomy pioneer [[Jan Oort]] also hypothesized the existence of dark matter in 1932.<ref name=Patras2014/><ref>{{cite journal |last=Oort |first=J.H. |author-link=Jan Oort |year=1932 |title=The force exerted by the stellar system in the direction perpendicular to the galactic plane and some related problems |journal=Bulletin of the Astronomical Institutes of the Netherlands |volume=6 |pages=249–287 |bibcode=1932BAN.....6..249O }}</ref><ref>{{cite web |title=The hidden lives of galaxies: Hidden mass |website=Imagine the Universe |publisher=[[NASA]] / [[GSFC]] |place=Greenbelt, MD |url=http://imagine.gsfc.nasa.gov/teachers/galaxies/imagine/hidden_mass.html }}</ref> Oort was studying stellar motions in [[Local Group|the galactic neighborhood]] and found the mass in the galactic plane must be greater than what was observed, but this measurement was later determined to be incorrect.<ref>{{cite journal |last1=Kuijken |first1=K. |last2=Gilmore |first2=G. |date=July 1989 |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=239 |issue=2 |pages=651–664 |bibcode=1989MNRAS.239..651K |title=The Mass Distribution in the Galactic Disc – Part III – the Local Volume Mass Density |doi=10.1093/mnras/239.2.651 |doi-access=free }}</ref>

In 1933, Swiss astrophysicist [[Fritz Zwicky]] studied [[galaxy cluster]]s while working at [[California Institute of Technology|Caltech]] and made a similar inference.<ref name=zwicky1933>{{cite journal |last=Zwicky |first=F. |author-link=Fritz Zwicky |date=1933 |title=Die Rotverschiebung von extragalaktischen Nebeln |trans-title=The red shift of extragalactic nebulae |journal=[[Helvetica Physica Acta]] |volume=6 |pages=110–127 |bibcode=1933AcHPh...6..110Z }}</ref>{{efn|
''"Um, wie beobachtet, einen mittleren Dopplereffekt von 1000&nbsp;km/sek oder mehr zu erhalten, müsste also die mittlere Dichte im Comasystem mindestens 400&nbsp;mal grösser sein als die auf Grund von Beobachtungen an leuchtender Materie abgeleitete. Falls sich dies bewahrheiten sollte, würde sich also das überraschende Resultat ergeben, dass dunkle Materie in sehr viel grösserer Dichte vorhanden ist als leuchtende Materie."''<ref name=zwicky1933/>{{rp|style=ama|p=125}}
: [In order to obtain an average Doppler effect of 1000&nbsp;km/s or more, as observed, the average density in the Coma system would thus have to be at least 400&nbsp;times greater than that derived on the basis of observations of luminous matter. If this were to be confirmed, the surprising result would then follow that dark matter is present in very much greater density than luminous matter.]
}}<ref name="zwicky1937">{{cite journal |last=Zwicky |first=Fritz |author-link=Fritz Zwicky |date=1937 |title=On the Masses of Nebulae and of Clusters of Nebulae |journal=[[The Astrophysical Journal]] |volume=86 |pages=217–246 |bibcode=1937ApJ....86..217Z |doi=10.1086/143864 |doi-access=free}}</ref> Zwicky applied the [[virial theorem]] to the [[Coma Cluster]] and obtained evidence of unseen mass he called {{Lang|de|dunkle Materie}} ('dark matter'). Zwicky estimated its mass based on the motions of galaxies near its edge and compared that to an estimate based on its brightness and number of galaxies. He estimated the cluster had about 400&nbsp;times more mass than was visually observable. The gravity effect of the visible galaxies was far too small for such fast orbits, thus mass must be hidden from view. Based on these conclusions, Zwicky inferred some unseen matter provided the mass and associated gravitational attraction to hold the cluster together.<ref>Some details of Zwicky's calculation and of more modern values are given in {{cite report |first=M. |last=Richmond |date=c. 1999 |title=Using the virial theorem: The mass of a cluster of galaxies |type=lecture notes |series=Physics&nbsp;440 |publisher=[[Rochester Institute of Technology]] |place=Rochester, NY |url=http://spiff.rit.edu/classes/phys440/lectures/gal_clus/gal_clus.html |via=spiff.rit.edu |access-date=10 July 2007}}</ref> Zwicky's estimates were off by more than an order of magnitude, mainly due to an obsolete value of the [[Hubble constant]];<ref>{{cite book |first=Katherine |last=Freese |year=2014 |title=The Cosmic Cocktail: Three parts dark matter |publisher=Princeton University Press |isbn=978-1-4008-5007-5 |url={{google books |plainurl=y |id=c2B8AgAAQBAJ}} }}</ref> the same calculation today shows a smaller fraction, using greater values for luminous mass. Nonetheless, Zwicky did correctly conclude from his calculation that most of the gravitational matter present was dark.<ref name=ArsTech-2017-02-03/> However unlike modern theories, Zwicky considered "dark matter" to be non-luminous ordinary matter.<ref name=GianfracoHooperHistory/>{{rp|III.A}}

Further indications of [[mass-to-light ratio]] anomalies came from measurements of [[galaxy rotation curve]]s. In 1939, [[Horace W. Babcock|H.W. Babcock]] reported the rotation curve for the [[Andromeda Galaxy|Andromeda nebula]] (now called ''the Andromeda Galaxy''), which suggested the mass-to-luminosity ratio increases radially.<ref name=Babcock-1939>{{cite journal |last=Babcock |first=H.W. |author-link=Horace W. Babcock |year=1939 |title=The rotation of the Andromeda Nebula |journal=[[Lick Observatory Bulletin]] |volume=19 |pages=41–51 |bibcode=1939LicOB..19...41B |doi=10.5479/ADS/bib/1939LicOB.19.41B |doi-access=free }}</ref> He attributed it to either light absorption within the galaxy or modified dynamics in the outer portions of the spiral, rather than to unseen matter. Following [[Horace W. Babcock|Babcock's]] 1939 report of unexpectedly rapid rotation in the outskirts of the Andromeda Galaxy and a mass-to-light ratio of 50; in 1940, [[Jan Oort|Oort]] discovered and wrote about the large non-visible halo of [[NGC 3115|NGC&nbsp;3115]].<ref>{{cite journal |last=Oort |first=J.H. |author-link=Jan Oort |date=April 1940 |title=Some problems concerning the structure and dynamics of the galactic system and the elliptical nebulae NGC&nbsp;3115 and 4494 |journal=[[The Astrophysical Journal]] |volume=91 |issue=3 |pages=273–306 |bibcode=1940ApJ....91..273O |doi=10.1086/144167 |hdl=1887/8533 |hdl-access=free |url=https://openaccess.leidenuniv.nl/bitstream/handle/1887/8533/008_653_032.pdf?sequence=1 |via=leidenuniv.nl }}</ref>