Editing Dark matter (section)

== History ==

=== 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>

=== 1970s ===
The hypothesis of dark matter largely took root in the 1970s. Several different observations were synthesized to argue that galaxies should be surrounded by halos of unseen matter. In two papers that appeared in 1974, this conclusion was drawn in tandem by independent groups: in [[Princeton, New Jersey]], by [[Jeremiah Ostriker]], [[Jim Peebles]], and [[Amos Yahil]], and in Tartu, Estonia, by [[Jaan Einasto]], [[Enn Saar]], and [[Ants Kaasik]].<ref name=DeSwart2024>{{cite journal |last1=de Swart |first1=Jaco |date=1 August 2024 |title=Five decades of missing mass |journal=[[Physics Today]] |volume=77 |pages=34–43 | doi=10.1063/pt.ozhk.lfeb |doi-access=free }}</ref>

One of the observations that served as evidence for the existence of galactic halos of dark matter was the shape of [[galaxy rotation curve]]s. These observations were done in optical and radio astronomy. In optical astronomy, [[Vera Rubin]] and [[Kent Ford (astronomer)|Kent Ford]] worked with a new [[spectrograph]] to measure the [[galaxy rotation curve|velocity curve]] of edge-on [[spiral galaxy|spiral galaxies]] with greater accuracy.<ref name=NYT-20161227>{{cite news |last=Overbye |first=D. |author-link=Dennis Overbye |date=27 December 2016 |title=Vera Rubin, 88, dies; opened doors in astronomy, and for women |type=obituary |newspaper=[[The New York Times]] |url=https://www.nytimes.com/2016/12/27/science/vera-rubin-astronomist-who-made-the-case-for-dark-matter-dies-at-88.html |access-date=27 December 2016 }}</ref><ref>{{cite web |title=First observational evidence of dark matter |website=Darkmatterphysics.com |url=http://www.darkmatterphysics.com/Galactic-rotation-curves-of-spiral-galaxies.htm |access-date=6 August 2013 |archive-url=https://web.archive.org/web/20130625183052/http://www.darkmatterphysics.com/Galactic-rotation-curves-of-spiral-galaxies.htm |archive-date=25 June 2013}}</ref><ref name=Rubin1970>{{cite journal |last1=Rubin |first1=V.C. |author1-link=Vera Rubin |last2=Ford |first2=W.K. Jr. |author2-link=Kent Ford (astronomer) |date=February 1970 |title=Rotation of the Andromeda nebula from a spectroscopic survey of emission regions |journal=[[The Astrophysical Journal]] |volume=159 |pages=379–403 |bibcode=1970ApJ...159..379R |doi=10.1086/150317 |s2cid=122756867 }}</ref>

At the same time, radio astronomers were making use of new [[Radio telescope|radio telescopes]] to map the [[21 cm line|21&nbsp;cm line]] of [[atomic hydrogen]] in nearby galaxies. The radial distribution of interstellar atomic hydrogen ([[H I region|H{{sup|{{math|I}}}}]]) often extends to much greater galactic distances than can be observed as collective starlight, expanding the sampled distances for rotation curves – and thus of the total mass distribution – to a new dynamical regime. Early mapping of [[Andromeda galaxy|Andromeda]] with the {{convert|300|ft|m|adj=mid}} telescope at [[Green Bank Observatory|Green Bank]]<ref name=Roberts1966>{{cite journal |last1=Roberts |first1=Morton S. <!-- |author-link1=Morton S. Roberts (astronomer) --> |date=May 1966 |title=A high-resolution 21&nbsp;cm hydrogen-line survey of the Andromeda nebula |journal=[[The Astrophysical Journal]] |volume=159 |pages=639–656 |bibcode=1966ApJ...144..639R |doi=10.1086/148645}}</ref> and the {{convert|250|ft|m|adj=mid}} dish at [[Jodrell Bank Observatory|Jodrell Bank]]<ref name="Gottesman1966">{{cite journal |last1=Gottesman |first1=S. T. <!-- |author-link1=S. T. Gottesman (astronomer) --> |last2=Davies |first2=Rod D. |author-link2=Rod Davies |last3=Reddish |first3=Vincent Cartledge |author-link3=Vincent Cartledge Reddish |date=1966 |title=A neutral hydrogen survey of the southern regions of the Andromeda nebula |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=133 |issue=4 |pages=359–387 |bibcode=1966MNRAS.133..359G |doi=10.1093/mnras/133.4.359 |doi-access=free}}</ref> already showed the H{{sup|{{math|I}}}} rotation curve did not trace the decline expected from Keplerian orbits.

As more sensitive receivers became available, <!-- [[Morton S. Roberts|-->Roberts<!--]]--> & <!-- [[Robert N. Whitehurst (astronomer) --- not the Olympic sailor --- |-->Whitehurst<!--]]--> (1975)<ref name=Roberts1975>{{cite journal |last1=Roberts |first1=Morton S.  <!-- |author-link1=Morton S. Roberts |last2=Whitehurst |first2=Robert N.  |author-link2=Robert N. Whitehurst (astronomer) --> |date=October 1975 |title=The rotation curve and geometry of M&nbsp;31 at large galactocentric distances |journal=[[The Astrophysical Journal]] |volume=201 |pages=327–346 |bibcode=1975ApJ...201..327R |doi=10.1086/153889}}</ref> were able to trace the rotational velocity of Andromeda to 30&nbsp;kpc, much beyond the optical measurements. Illustrating the advantage of tracing the gas disk at large radii; that paper's ''Figure&nbsp;16''<ref name=Roberts1975/> combines the optical data<ref name=Rubin1970/> (the cluster of points at radii of less than 15&nbsp;kpc with a single point further out) with the H{{sup|{{math|I}}}} data between 20 and 30&nbsp;kpc, exhibiting the flatness of the outer galaxy rotation curve; the solid curve peaking at the center is the optical surface density, while the other curve shows the cumulative mass, still rising linearly at the outermost measurement. In parallel, the use of interferometric arrays for extragalactic H{{sup|{{math|I}}}} spectroscopy was being developed. <!-- [[David H. Rogstad (astronomer)| -->Rogstad<!-- ]] --> & [[Seth Shostak|Shostak]] (1972)<ref name=Rogstad1972/> published H{{sup|{{math|I}}}} rotation curves of five spirals mapped with the Owens Valley interferometer; the rotation curves of all five were very flat, suggesting very large values of mass-to-light ratio in the outer parts of their extended H{{sup|{{math|I}}}}&nbsp;disks.<ref name="Rogstad1972">{{cite journal |last1=Rogstad |first1=David H. <!-- |author-link1=David H. Rogstad (astronomer) --> |last2=Shostak |first2=G. Seth |author-link2=Seth Shostak |date=September 1972 |title=Gross properties of five Scd galaxies as determined from 21&nbsp;centimeter observations |journal=[[The Astrophysical Journal]] |volume=176 |pages=315–321 |bibcode=1972ApJ...176..315R |doi=10.1086/151636}}</ref> In 1978, Albert Bosma showed further evidence of flat rotation curves using data from the [[Westerbork Synthesis Radio Telescope]].<ref>{{cite thesis |last=Bosma |first=A. |date=1978 |title=The distribution and kinematics of neutral hydrogen in spiral galaxies of various morphological types |degree=Ph.D. |publisher=[[Rijksuniversiteit Groningen]] |url=http://nedwww.ipac.caltech.edu/level5/March05/Bosma/frames.html}}</ref>

In 1978, [[Gary Steigman|Steigman]] et al.<ref>{{cite journal |last=Gunn |first=J. E. |last2=Lee |first2=B. W. |last3=Lerche |first3=I. |last4=Schramm |first4=D. N. |last5=Steigman |first5=G. |date=Aug 1978 |title=Some astrophysical consequences of the existence of a heavy stable neutral lepton. |url=https://ui.adsabs.harvard.edu/abs/1978ApJ...223.1015G/abstract |journal=The Astrophysical Journal |language=en |volume=223 |pages=1015–1031 |doi=10.1086/156335 |issn=0004-637X}}</ref> presented a study that extended earlier cosmological relic-density calculations to any hypothetical stable, electrically neutral, weak-scale lepton, showing how such a particle's abundance would "freeze out" in the [[Early universe|early Universe]] and providing analytic expressions that linked its mass and weak interaction cross-section to the present-day matter density. By decoupling the analysis from specific [[neutrino]] properties and treating the candidate generically, the authors set out a framework that later became the standard template for [[weakly interacting massive particle]]s (WIMPs)<ref>{{cite book |last=Tan |first=Chung-i |url=https://www.google.com.br/books/edition/Particles_Strings_And_Supernovae_Proceed/CtBKDwAAQBAJ |title=Particles, Strings And Supernovae - Proceedings Of Theoretical Advanced Study Institute In Elementary Particle Physics (In 2 Volumes) |last2=Jevicki |first2=Antal |date=1989-05-01 |publisher=World Scientific |isbn=978-981-4590-77-8 |pages=191 |language=en}}</ref> and for comparing [[Particle physics|particle-physics]] models with cosmological constraints. Though subsequent work has refined the methodology and explored many alternative candidates, this paper marked the first explicit, systematic treatment of dark matter as a new particle species beyond the [[Standard Model]].<ref>{{citation |last=Mambrini |first=Yann |title=Introduction |date=2021 |work=Particles in the Dark Universe: A Student’s Guide to Particle Physics and Cosmology |pages=1–22 |editor-last=Mambrini |editor-first=Yann |url=https://link.springer.com/chapter/10.1007/978-3-030-78139-2_1 |access-date=2025-04-26 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-78139-2_1 |isbn=978-3-030-78139-2}}</ref> 

By the late 1970s the existence of dark matter halos around galaxies was widely recognized as real, and became a major unsolved problem in astronomy.<ref name=DeSwart2024/>

=== 1980–1990s ===
A stream of observations in the 1980–1990s supported the presence of dark matter. {{harvp|Persic|Salucci|Stel|1996}} is notable for the investigation of 967&nbsp;spirals.<ref>{{cite journal |first1=Massimo |last1=Persic |first2=Paolo |last2=Salucci |first3=Fulvio |last3=Stel |year=1996 |title=The universal rotation curve of spiral galaxies — I.&nbsp;The dark matter connection  |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=281  |issue=1 |pages=27–47 |doi= 10.1093/mnras/278.1.27 |doi-access=free |arxiv=astro-ph/9506004 |bibcode= 1996MNRAS.281...27P }}</ref> The evidence for dark matter also included [[gravitational lensing]] of background objects by [[galaxy cluster]]s,<ref name=Randall_2015/>{{rp|style=ama|pp= 14–16}} the temperature distribution of hot gas in galaxies and clusters, and the pattern of anisotropies in the [[cosmic microwave background]].

According to the current consensus among cosmologists, dark matter is composed primarily of some type of not-yet-characterized [[subatomic particle]].<ref name="Copi 1995">{{cite journal |last1=Copi |first1=C.J. |last2=Schramm |first2=D.N. |last3=Turner |first3=M.S. |year=1995 |title=Big-Bang nucleosynthesis and the baryon density of the universe |journal=[[Science (journal)|Science]] |volume=267 |issue=5195 |pages=192–199 |arxiv=astro-ph/9407006 |bibcode=1995Sci...267..192C |doi=10.1126/science.7809624 |pmid=7809624 |s2cid=15613185 |url=https://cds.cern.ch/record/265576 }}</ref><ref name="Bergstrom 2000">{{cite journal |last=Bergstrom |first=L. |year=2000 |title=Non-baryonic dark matter: Observational evidence and detection methods |journal=[[Reports on Progress in Physics]] |volume=63 |issue=5 |pages=793–841 |arxiv=hep-ph/0002126 |bibcode=2000RPPh...63..793B |doi=10.1088/0034-4885/63/5/2r3 |s2cid=119349858 }}</ref>
The search for this particle, by a variety of means, is one of the major efforts in [[particle physics]].<ref name="bertone hooper silk">{{cite journal |last1=Bertone |first1=G. |last2=Hooper |first2=D. |last3=Silk |first3=J. |year=2005 |title=Particle dark matter: Evidence, candidates, and constraints |journal=[[Physics Reports]] |volume=405 |issue=5–6 |pages=279–390 |arxiv=hep-ph/0404175 |bibcode=2005PhR...405..279B |doi=10.1016/j.physrep.2004.08.031 |s2cid=118979310 }}</ref>