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

The rotation curve of a galaxy can be represented by a graph that plots the orbital velocity of the stars or gas in the galaxy on the y-axis against the distance from the center of the galaxy on the x-axis. Stars revolve around the center of galaxies at a constant speed over a large range of distances from the center of the galaxy. Thus they revolve much faster than would be expected if they were in a free Newtonian potential. The galaxy rotation problem is this discrepancy between the observed rotation speeds of matter in the disk portions of spiral galaxies and the predictions of Newtonian dynamics considering the visible mass. This discrepancy is currently thought to betray the presence of dark matter that permeates the galaxy and extends into the galaxy's halo. Image File history File links GalacticRotation2. ... Image File history File links GalacticRotation2. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ... 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. ... This article is about the astronomical object. ... A gas is one of the four major phases of matter (after solid and liquid, and followed by plasma, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... The Newtonian potential is an operator in vector calculus that acts as the inverse to the negative Laplacian, on functions that are smooth and decay rapidly enough at infinity. ... 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. ... Dark matter is a term used in astrophysics to refer to that component of the universe that is unaccounted for, unexplained or inconclusively explained, and whose existence at this time is only inferred. ... Beyond the visible, inner portion of the galactic halo lies a much larger region, known as the dark matter halo which contains large amounts of dark matter. ...

History and description of the problem

In 1978, the first observational evidence was reported that spiral galaxies do not spin as expected according to Keplerian dynamics.^[1] 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. 1978 (MCMLXXVIII) was a common year starting on Sunday. ... Johannes Kepler Johannes Kepler (December 27, 1571 – November 15, 1630), a key figure in the scientific revolution, was a German astronomer, mathematician and astrologer. ... This article or section does not cite its references or sources. ... 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. ... This article is about the Solar System. ... It has been suggested that this article or section be merged with Classical mechanics. ... 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. William of Ockham. ... Physics (from the Greek, (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the discovery and understanding of the fundamental laws which govern matter, energy, space, and time. ... Dark matter is a term used in astrophysics to refer to that component of the universe that is unaccounted for, unexplained or inconclusively explained, and whose existence at this time is only inferred. ... Beyond the visible, inner portion of the galactic halo lies a much larger region, known as the dark matter halo which contains large amounts of dark matter. ... 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... A pie chart indicating the proportional composition of different energy-density components of the universe. ... Cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... The universe from a speculative theoretical physicists point of view can be described as the sum of all matter and energy that exists and the space-time in which they are located and in which all events occur or could occur. ...

Further investigations

Having been important in convincing people of the existence of dark matter, recent work on galaxy rotation curves provides some of its greatest challenges. Detailed investigations of the rotation curves of low surface brightness galaxies (LSB galaxies) in the 1990s^[2] and of their position on the Tully-Fisher relation^[3] showed that these did not behave as expected. These galaxies had to be dominated by dark matter in a surprising fashion. However, such dark matter-dominated dwarf galaxies may hold the key to solving the dwarf galaxy problem of structure formation. A low surface brightness galaxy or LSB galaxy is a diffuse galaxy with a surface brightness that, when viewed from Earth, is at least one magnitude lower than the ambient night sky. ... In astronomy, the Tully-Fisher relation, published by astronomers R. Brent Tully and J. Richard Fisher in 1977, is a standard candle that measures the distance to rotating spiral galaxies by the width of the galaxys spectral lines. ... Wikipedia does not yet have an article with this exact name. ... The dwarf galaxy problem is one that arises from numerical cosmological simulations that predict the evolution of the distribution of matter in the universe. ... It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ...

Further challenges to dark matter theory, or at least its most popular form - cold dark matter (CDM), came from analysis of the centres of low surface brightness galaxies. Numerical simulations based on CDM gave predictions of the shape of the rotation curves in the centre of dark-matter dominated systems, such as these galaxies. Observations of the actual rotation curves did not show the predicted shape.^[4]. This so-called cuspy halo problem of cold dark matter is considered a tractable issue by theoretical cosmologists. 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... The cuspy halo problem is one that arises from cosmological simulations that seem to indicate cold dark matter would form cuspy distributions in the most dense areas of the universe. ...

That dark matter theory has continued to be supported as an explanation for galaxy rotation curves is due to the fact that the evidence for dark matter is not solely that from these curves. It has been uniquely successful in simulating the formation of the large scale structure seen in the distribution of galaxies and in explaining the dynamics of groups and clusters of galaxies (as originally proposed by Zwicky). Dark matter also correctly predicts the results of gravitational lensing observations. This article is in need of attention from an expert on the subject. ...

Dark matter alternatives

There are a limited number of attempts to find alternative explanations to dark matter to explain galaxy rotation curves. One of the most discussed alternatives is MOND (Modified Newtonian Dynamics), originally proposed as a phenomenological explanation back in 1983 but which has been seen to have predictive power in the rotation curves of LSB galaxies. This posits that the physics of gravity changes at large scale but, until recently, was not a relativistic theory. However, this has now changed with the development of the tensor-vector-scalar gravity (TeVeS) theory^[5] and scalar-tensor-vector gravity (STVG)^[6]. None of these alternatives is yet considered by the astronomical community to be as convincing as the dark matter model ^[7]. Recently, observations of the Bullet Cluster have cast considerable doubt on the ability for MOND and other dark matter alternatives to explain the sum total of evidence for dark matter. Dark matter is a term used in astrophysics to refer to that component of the universe that is unaccounted for, unexplained or inconclusively explained, and whose existence at this time is only inferred. ... Wikipedia does not yet have an article with this exact name. ... Gravity is a force of attraction that acts between bodies that have mass. ... This article or section is in need of attention from an expert on the subject. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... The scientific community consists of the interactions and relationships of scientists. ... The Bullet cluster (1E 0657-56) consists of two colliding clusters of galaxies. ...

See also

• Vera Rubin

Vera (Cooper) Rubin (born 23 July 1928) is an astronomer who has done pioneering work on galaxy rotation rates. ...

Bibliography

• V. Rubin, W. K. Ford, Jr (1970). "Rotation of the Andromeda Nebula from a Spectroscopic Survey of Emission Regions". Astrophysical Journal 159: 379.

  This was the first detailed study of orbital rotation in galaxies.

• V. Rubin, W. K. Ford, Jr, N. Thonnard (1980). "Rotational Properties of 21 Sc Galaxies with a Large Range of Luminosities and Radii from NGC 4605 (R=4kpc) to UGC 2885 (R=122kpc)". Astrophysical Journal 238: 471.

  Observations of a set of spiral galaxies gave convincing evidence that orbital velocities of stars in galaxies were unexpectedly high at large distances from the nucleus. This paper was influential in convincing astronomers that most of the matter in the universe is dark, and much of it is clumped about galaxies.

• Galactic Dynamics, James Binney and Scott Tremaine.Princeton University Press 1987. ISBN 0-691-08444-0 (cloth); ISBN 0-691-08445-9 (paperback)

• J. R. Brownstein and J. W. Moffat (2006). "Galaxy Rotation Curves Without Non-Baryonic Dark Matter". Astrophysical Journal 636: 721.

  Arxiv.org Preprint (astro-ph/0506370)

The Uppsala General Catalogue of Galaxies (UGC) is a catalogue of 12921 galaxies visible from the northern hemisphere. ... The Princeton University Press is a publishing house, a division of Princeton University, that is highly respected in academic publishing. ...

Footnotes

1. ^ A. Bosma, "The distribution and kinematics of neutral hydrogen in spiral galaxies of various morphological types", PhD Thesis, Rejksuniversiteit Groningen, 1978, available online at the Nasa Extragalactic Database
2. ^ W. J. G. de Blok, S. McGaugh (1997). "The dark and visible matter content of low surface brightness disc galaxies". Monthly Notices of the Royal Astronomical Society 290: 533-552. available online at the Smithsonian/NASA Astrophysics Data System
3. ^ M. A. Zwaan, J. M. van der Hulst, W. J. G. de Blok, S. McGaugh (1995). "The Tully-Fisher relation for low surface brightness galaxies: implications for galaxy evolution". Monthly Notices of the Royal Astronomical Society 273: L35-L38. available online at the Smithsonian/NASA Astrophysics Data System
4. ^ W. J. G. de Blok, A. Bosma (2002). "High-resolution rotation curves of low surface brightness galaxies". Astronomy & Astrophysics 385: 816-846. available online at the Smithsonian/NASA Astrophysics Data System
5. ^ J. D. Bekenstein (2004). "Relativistic gravitation theory for the modified Newtonian dynamics paradigm". Physical Review D 70: 083509.
6. ^ J. W. Moffat (2006). "Scalar tensor vector gravity theory". Journal of Cosmology and Astroparticle Physics 3: 4.
7. ^ See, for example, the review of the development of the subject by BBC science reporters, and this commentary by astronomers involved with the Chandra X-Ray Observatory [1]. The astronomical community accepts the existence and presence of dark matter due as well to corroboration by observations unrelated to galaxy rotation curves including gravitational lensing, measurements of the cosmic microwave background radiation, and statistics of the large scale structure of the universe.