The galaxy rotation problem is the discrepancy between the observed rotation speeds of matter in the disk portions of spiral galaxies and the predictions of Newtonian dynamics considering the luminous mass. The presence of this discrepancy is explained by astronomers as pointing to the existence of dark matter in the halo of the galaxy. A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ... In the article vector quantities are written in bold whereas scalar ones are in italics. ... // This refers to the cosmological use of the term. ... The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ...

Fig. 1 -- Rotation curve of a typical spiral galaxy: predicted (A) and observed (B).

In the beginning of the 1980s, the first observational evidence was reported that spiral galaxies do not spin as expected according to Keplerian dynamics. Based on this model, matter (such as stars and gas) in the disk portion of a spiral should orbit the center of the galaxy similar to the way in which planets in the solar system orbit the sun, that is, according to Newtonian mechanics. Based on this, it would be expected that the average orbital speed of an object at a specified distance away from the majority of the mass distribution would decrease inversely with the square root of the radius of the orbit (the dashed line in Fig. 1). At the time of the discovery of the discrepancy, it was thought that most of the mass of the galaxy had to be in the galactic bulge, near the center. Image File history File links GalacticRotation2. ... Image File history File links GalacticRotation2. ... The 1980s decade refers to the years from 1980 to 1989, inclusive. ... Johannes Kepler Johannes Kepler (December 27, 1571 – November 15, 1630), a key figure in the scientific revolution, was a German astronomer, mathematician and astrologer. ... Matter is commonly defined as the substance of which physical objects are composed. ... For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... Presentation of the solar system (not to scale) The solar system comprises the Earths Sun and the retinue of celestial objects gravitationally bound to it. ... The original version of the physical discipline of mechanics, due to Sir Isaac Newton, who developed the theory over a period from about 1664, until the publication of his great work, known as the Principia, in 1687. ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ... In astronomy, a bulge is a huge, tightly packed group of stars. ...

Observations of the rotation curve of spirals, however, do not bear this out. Rather, the curves do not decrease in the expected inverse square root relationship but are "flat" -- outside of the central bulge the speed is nearly a constant function of radius (the solid line Fig. 1). The explanation that requires the least adjustment to the physical laws of the universe is that there is a substantial amount of matter far from the center of the galaxy that is not emitting light in the mass-to-light ratio of the central bulge. This extra mass is proposed by astronomers to be due to dark matter within the galactic halo, the existence of which was first posited by Fritz Zwicky some 40 years earlier in his studies of the masses of galaxy clusters. Presently, there are a large number of pieces of observational evidence that point to the presence of cold dark matter, and its existence is a major feature of the present Lambda-CDM model that describes the cosmology of the universe. The rotation curve of a galaxy; that is, the orbital velocity as a function of distance from the centre of the galaxy. ... A Superconductor demonstrating the Meissner Effect. ... // This refers to the cosmological use of the term. ... The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ... Fritz Zwicky (February 14, 1898 – February 8, 1974) was an American-based Swiss astronomer. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ... Cold dark matter (or CDM) is a refinement of the big bang theory that contains the additional assumption that most of the matter in the Universe consists of material which cannot be observed by its electromagnetic radiation and hence is dark while at the same time the particles making up... ΛCDM or Lambda-CDM is an abbreviation for Lambda-Cold Dark Matter. ... Cosmology, from the Greek: κοσμολογία (cosmologia, κόσμος (cosmos) world + λογια (logia) discourse) is the study of the universe in its totality and by extension mans place in it. ... This article needs to be updated. ...

A small minority of physicists and astronomers have expressed discomfort with the dark matter theory and some have offered alternative explanations. One alternative is Modified Newtonian Dynamics (MOND) theory, which posits that the physics of gravity changes at large scales. Other modifications of gravity that try to explain the mystery of the rotational curves are Nonsymmetric Gravitational Theory and conformal gravity. More recently, it has been suggested that general relativity can resolve the anomalies. Advocates of various nonstandard cosmologies have provided alternative explanations with varying levels of sophistication, among them plasma cosmology, quasi-steady state cosmology, and ideas advocated by Halton Arp. None of these alternatives are considered by the vast majority of the astronomical community to be as convincing as the dark matter model ^[1]. In physics, the modified Newtonian dynamics (MOND) is a burgeoning theory that attempts to explain the galaxy rotation problem by modifying Newtons second law of motion. ... Gravity is a force of attraction that acts between bodies that have mass. ... Nonsymmetric Gravitational Theory is a modification of Einsteins theory of General Relativity that tries to explain the mystery of Dark Matter. ... This is a generic name for gravity theories which are invariant under conformal transformations in the Riemannian geometric sense. ... A non-standard cosmology is a cosmological framework that contradicts the standard model of physical cosmology. ... Plasma Universe and plasma cosmology. ... The quasi-steady state cosmology is a non-standard cosmology suggesting that, rather than a single Big Bang, there have been many, occurring over time. ... Halton Arp in London, Oct 2000 Halton Christian Arp is an American astronomer. ...

See also

• Vera Rubin

check out http://telecomm1.blogspot.com Vera (Cooper) Rubin (born 23 July 1928) is an astronomer who has done pioneering work on galaxy rotation rates. ...

References

1. ^  General Relativity Resolves Galactic Rotation…
2. ^  Singular disk of matter in the Cooperstock…
3. ^  See, for example, the review of the development of the subject by BBC science reporters.