History Dark matter

early history

the hypothesis of dark matter has elaborate history. in talk given in 1884, lord kelvin estimated number of dark bodies in milky way galaxy observed velocity dispersion of stars, speed stars orbiting around center of galaxy, used estimate mass of galaxy, different mass of stars can seen, , concluded “many of our stars, perhaps great majority of them, may dark bodies.”

in 1906 henri poincaré in “the milky way , theory of gases” used dark matter,” or “matière obscure” in french in discussing kelvin s work.

the first suggest existence of dark matter (using stellar velocities) dutch astronomer jacobus kapteyn in 1922. fellow dutchman , radio astronomy pioneer jan oort hypothesized existence of dark matter in 1932. oort studying stellar motions in local galactic neighborhood , found mass in galactic plane must greater observed, measurement later determined erroneous.

in 1933, swiss astrophysicist fritz zwicky, studied galactic clusters while working @ california institute of technology, made similar inference. zwicky applied virial theorem coma cluster , obtained evidence of unseen mass called dunkle materie dark matter . zwicky estimated mass based on motions of galaxies near edge , compared estimate based on brightness , number of galaxies. estimated cluster had 400 times more mass visually observable. gravity effect of visible galaxies far small such fast orbits, mass must hidden view. based on these conclusions, zwicky inferred unseen matter provided mass , associated gravitation attraction hold cluster together. first formal inference existence of dark matter. zwicky s estimates off more order of magnitude, due obsolete value of hubble constant; same calculation today shows smaller fraction, using greater values luminous mass. however, zwicky did correctly infer bulk of matter dark.

the first robust indications mass light ratio other unity came measurements of galaxy rotation curves. in 1939, horace w. babcock reported rotation curve andromeda nebula (known andromeda galaxy), suggested mass-to-luminosity ratio increases radially. attributed either light absorption within galaxy or modified dynamics in outer portions of spiral , not missing matter.

1970s

vera rubin , kent ford in 1960s–1970s provided further strong evidence, using galaxy rotation curves. rubin worked new spectrograph measure velocity curve of edge-on spiral galaxies greater accuracy. result confirmed in 1978. influential paper presented rubin s results in 1980. rubin found galaxies must contain 6 times dark visible mass; thus, around 1980 apparent need dark matter recognized major unsolved problem in astronomy.

at same time rubin , ford exploring optical rotation curves, radio astronomers making use of new radio telescopes map 21 cm line of atomic hydrogen in nearby galaxies. radial distribution of interstellar atomic hydrogen extends larger galactic radii accessible optical studies, allowing sampling of rotation curves – , of total mass distribution – new dynamical regime. mapping of andromeda 300-foot telescope @ green bank , 250-foot dish @ jodrell bank showed hi rotation curve did not trace expected keplerian decline. more sensitive receivers became available, morton roberts , robert whitehurst able trace rotational velocity of andromeda 30 kpc, beyond optical measurements. illustrating advantage of tracing gas disk @ large radii, figure 16 of paper combines optical data (the cluster of points @ radii of less 15 kpc single point further out) hi data between 20 , 30 kpc, exhibiting flatness of outer galaxy rotation curve; solid curve peaking @ center optical surface density, while other curve shows cumulative mass, still rising linearly @ outermost measurement. in parallel, use of interferometric arrays extragalactic hi spectroscopy being developed. in 1972, david rogstad , seth shostak published hi rotation curves of 5 spirals mapped owens valley interferometer; rotation curves of 5 flat, suggesting large values of mass-to-light ratio in outer parts of extended hi disks.

a stream of observations in 1980s indicated presence, including gravitational lensing of background objects galaxy clusters, temperature distribution of hot gas in galaxies , clusters, , pattern of anisotropies in cosmic microwave background. according consensus among cosmologists, dark matter composed of not yet characterized type of subatomic particle. search particle, variety of means, 1 of major efforts in particle physics.