|
In physics and cosmology, dark matter is matter that does not interact with the electromagnetic force, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structures larger than galaxies, as well as Big Bang cosmology, dark matter accounts for the vast majority of mass in the observable universe. The observed phenomena which imply the presence of dark matter include the rotational speeds of galaxies, orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter also plays a central role in structure formation and galaxy evolution, and has measurable effects on the anisotropy of the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation: the remainder is called the "dark matter component." Dark matter, the hypothetical matter particle Dark Matter, a science fiction book Dark Matter (fiction), the use of dark matter in fiction books This is a disambiguation page—a list of articles associated with the same title. ...
This article is about the physics subject. ...
For other uses, see Universe (disambiguation). ...
For other uses, see Big Bang (disambiguation). ...
This box: This article is about scientific estimates of the age of the universe. ...
This box: A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events according to the scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates. ...
This box: The ultimate fate of the universe is a topic in physical cosmology. ...
In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ...
This article or section is in need of attention from an expert on the subject. ...
The Cosmic Neutrino Background (CNB) is the background particle radiation composed of neutrinos. ...
CMB redirects here. ...
This article is about the physical phenomenon. ...
This box: Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ...
This box: The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ...
The Friedmann equations relate various cosmological parameters within the context of general relativity. ...
// The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ...
The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ...
It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ...
In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space...
This box: In physical cosmology, the term large-scale structure refers to the characterization of observable distributions of matter and light on the largest scales (typically on the order of billions of light-years). ...
A pie chart indicating the proportional composition of different energy-density components of the universe. ...
In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ...
For a timeline of the cosmos (or universe), see Timeline of the Big Bang. ...
This box: A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events according to the scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates. ...
Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. ...
In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Gurvey), or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory in the 1990s. ...
SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ...
The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ...
The Telescope being readied for launch The BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics) measured the cosmic microwave background radiation of a part of the sky during three sub-orbital (high altitude) balloon flights. ...
Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ...
“Einstein†redirects here. ...
Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ...
Alexander Alexandrovich Friedman or Friedmann (ÐлекÑандр ÐлекÑандрович Фридман) (June 16, 1888 – September 16, 1925) was a Russian cosmologist and mathematician. ...
Monsignor Georges Lemaître, priest and scientist. ...
Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ...
Arno Allan Penzias (born April 26, 1933) is an American physicist and winner of the 1978 Nobel Prize in physics. ...
Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ...
George Gamow (pronounced GAM-off) (March 4, 1904 – August 19, 1968) , born Georgiy Antonovich Gamov (Георгий Ðнтонович Гамов) was a Ukrainian born physicist and cosmologist. ...
Robert Henry Dicke (May 6, 1916 – March 4, 1997) was an American experimental physicist, who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity. ...
Yakov Borisovich Zeldovich (Russian:Яков БориÑович Зельдович) (March 8, 1914 – December 2, 1987) was a prolific Soviet physicist. ...
John Cromwell Mather (b. ...
Vera (Cooper) Rubin (born 23 July 1928) is an astronomer who has done pioneering work on galaxy rotation rates. ...
George Fitzgerald Smoot III (born February 20, 1945) is an American astrophysicist and cosmologist awarded the 2006 Nobel Prize in Physics with John C. Mather for their discovery of the black body form and anisotropy of the cosmic microwave background radiation. This work helped cement the big-bang theory of...
This is a list of cosmologists. ...
A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ...
This article is about the physics subject. ...
This article is about matter in physics and chemistry. ...
Gravity is a force of attraction that acts between bodies that have mass. ...
This article is about a celestial body. ...
For other uses, see Big Bang (disambiguation). ...
The mass of the observable universe can be estimated using estimations for its density and size. ...
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. ...
This article is about a celestial body. ...
Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...
A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ...
The Bullet cluster (1E 0657-56) consists of two colliding clusters of galaxies. ...
It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ...
In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space...
Look up anisotropy in Wiktionary, the free dictionary. ...
WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ...
A hadron, in particle physics, is a subatomic particle which experiences the nuclear force. ...
The dark matter component has vastly more mass than the "visible" component of the universe.[1] At present, the density of ordinary baryons and radiation in the universe is estimated to be equivalent to about one hydrogen atom per cubic meter of space. Only about 4% of the total energy density in the universe (as inferred from gravitational effects) can be seen directly. About 22% is thought to be composed of dark matter. The remaining 74% is thought to consist of dark energy, an even stranger component, distributed diffusely in space.[2] Some hard-to-detect baryonic matter makes a contribution to dark matter but constitutes only a small portion.[3][4] Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics. It has been noted that the names "dark matter" and "dark energy" serve mainly as expressions of human ignorance, much as the marking of early maps with "terra incognita."[2] For other uses, see Universe (disambiguation). ...
Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ...
For other uses, see Light (disambiguation). ...
In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ...
Baryonic dark matter is the dark matter (matter that doesnt emit light) composed of baryons, i. ...
Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...
Terra incognita is a term used in exploration for unknown territory that has not been mapped or documented. ...
[edit] Observational evidence The first to provide evidence and infer the existence of a phenomenon that has come to be called "dark matter" was Swiss astrophysicist Fritz Zwicky, of the California Institute of Technology (Caltech) in 1933.[5] He applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass. Zwicky estimated the cluster's total mass based on the motions of galaxies near its edge. When he compared this mass estimate to one based on the number of galaxies and total brightness of the cluster, he found that there was about 400 times more mass than expected. The gravity of the visible galaxies in the cluster would be far too small for such fast orbits, so something extra was required. This is known as the "missing mass problem". Based on these conclusions, Zwicky inferred that there must be some non-visible form of matter which would provide enough of the mass and gravity to hold the cluster together. Fritz Zwicky (February 14, 1898 – February 8, 1974) was an American-based Swiss astronomer. ...
The California Institute of Technology (commonly referred to as Caltech)[1] is a private, coeducational research university located in Pasadena, California, in the United States. ...
In mechanics, the virial theorem provides a general equation relating the average total kinetic energy of a system with its average total potential energy , where angle brackets represent the average of the enclosed quantity. ...
The Coma Cluster is an huge galaxy cluster and the prototypical rich cluster with over a thousand member galaxies known. ...
Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...
Much of the evidence for dark matter comes from the study of the motions of galaxies. Many of these appear to be fairly uniform, so by the virial theorem the total kinetic energy should be half the total gravitational binding energy of the galaxies. Experimentally, however, the total kinetic energy is found to be much greater: in particular, assuming the gravitational mass is due to only the visible matter of the galaxy, stars far from the center of galaxies have much higher velocities than predicted by the virial theorem. Galactic rotation curves, which illustrate the velocity of rotation versus the distance from the galactic center, cannot be explained by only the visible matter. Assuming that the visible material makes up only a small part of the cluster is the most straightforward way of accounting for this. Galaxies show signs of being composed largely of a roughly spherically symmetric, centrally concentrated halo of dark matter with the visible matter concentrated in a disc at the center. Low surface brightness dwarf galaxies are important sources of information for studying dark matter, as they have an uncommonly low ratio of visible matter to dark matter, and have few bright stars at the center which impair observations of the rotation curve of outlying stars. Image File history File links 060821_darkmatter. ...
Image File history File links 060821_darkmatter. ...
The Bullet cluster (1E 0657-56) consists of two colliding clusters of galaxies. ...
In physics, emission is the process by which the energy of a photon is released by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ...
This article or section is in need of attention from an expert on the subject. ...
For other uses, see Galaxy (disambiguation). ...
The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ...
The gravitational binding energy of an object is the amount of energy required to accelerate every component of that object to the escape velocity of every other component. ...
Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ...
Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). ...
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. ...
A low surface brightness galaxy or LSB galaxy is a diffuse galaxy with a surface brightness that is one magnitude lower than the ambient night sky. ...
The most direct observational evidence to date for dark matter is in a system known as the Bullet Cluster. A collision between two galaxy clusters appears to have caused a separation of dark matter and baryonic matter. X-ray observations show that much of the baryonic matter (in the form of hot gas) in the system is concentrated in the center of the system. Collisions between gas particles caused them to slow down. However, gravitational lensing observations of the same system show much of the mass to reside outside of the central region of baryonic gas. Because dark matter does not interact by collisions, it would not have been slowed in the same way as the X-ray visible gas, so the dark matter in the two clusters passed through each other without slowing down substantially. This accounts for the separation. This is held as direct evidence of the existence of dark matter, independent of Newtonian gravity.[7][8] The Bullet cluster (1E 0657-56) consists of two colliding clusters of galaxies. ...
Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...
ROSAT image of X-ray fluorescence of, and occultation of the X-ray background by, the Moon. ...
This article or section is in need of attention from an expert on the subject. ...
The law of universal gravitation states that gravitational force between masses decreases with the distance between them, according to an inverse-square law. ...
[edit] Galactic rotation curves -
 Rotation curve of a typical spiral galaxy: predicted ( A) and observed ( B). Dark matter can explain the velocity curve having a "flat" appearance out to a large radius For 40 years after Zwicky's initial observations, no other corroborating observations indicated that the mass to light ratio was anything other than unity (a high mass-to-light ratio indicates the presence of dark matter). Then, in the late 1960s and early 1970s, Vera Rubin, a young astronomer at the Department of Terrestrial Magnetism at the Carnegie Institution of Washington presented findings based on a new sensitive spectrograph that could measure the velocity curve of edge-on spiral galaxies to a greater degree of accuracy than had ever before been achieved. Together with fellow staff-member Kent Ford, Rubin announced at a 1975 meeting of the American Astronomical Society the astonishing discovery that most stars in spiral galaxies orbit at roughly the same speed, which implied that their mass densities were uniform well beyond the locations with most of the stars (the galactic bulge). This result suggests that either Newtonian gravity does not apply universally or that, conservatively, upwards of 50% of the mass of galaxies was contained in the relatively dark galactic halo. Met with skepticism, Rubin insisted that the observations were correct. Eventually other astronomers began to corroborate her work and it soon became well-established that most galaxies were in fact dominated by "dark matter"; exceptions appeared to be galaxies with mass-to-light ratios close to that of stars. Subsequent to this, numerous observations have been made that do indicate the presence of dark matter in various parts of the cosmos. Together with Rubin's findings for spiral galaxies and Zwicky's work on galaxy clusters, the observational evidence for dark matter has been collecting over the decades to the point that today most astrophysicists accept its existence. As a unifying concept, dark matter is one of the dominant features considered in the analysis of structures on the order of galactic scale and larger. Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). ...
Image File history File links GalacticRotation2. ...
Image File history File links GalacticRotation2. ...
In physical cosmology the mass to light ratio is a comparison of the total mass of a galaxy or a cluster compared to its luminosity. ...
Vera (Cooper) Rubin (born 23 July 1928) is an astronomer who has done pioneering work on galaxy rotation rates. ...
The Carnegie Institution of Washington (CIW) is a foundation established by Andrew Carnegie in 1902 to support scientific research. ...
For Acoustic uses in spectrographs of sound waves, see below. ...
Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). ...
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. ...
The American Astronomical Society (AAS) is a US society of professional astronomers and other interested individuals, headquartered in Washington, DC. The main aim of the AAS is provide a political voice for its members and organise their lobbying. ...
This article is about the astronomical object. ...
An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) A spiral galaxy is a galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulaeâ€[1] and, as...
In astronomy, a bulge is a huge, tightly packed group of stars. ...
Gravity is a force of attraction that acts between bodies that have mass. ...
[edit] Velocity dispersions of galaxies Rubin's pioneering work has stood the test of time. Measurements of velocity curves in spiral galaxies were soon followed up with velocity dispersions of elliptical galaxies. While sometimes appearing with lower mass-to-light ratios, measurements of ellipticals still indicate a relatively high dark matter content. Likewise, measurements of the diffuse interstellar gas found at the edge of galaxies indicate not only dark matter distributions that extend beyond the visible limit of the galaxies, but also that the galaxies are virialized up to ten times their visible radii. This has the effect of pushing up the dark matter as a fraction of the total amount of gravitating matter from 50% measured by Rubin to the now accepted value of nearly 95%. The giant elliptical galaxy ESO 325-G004. ...
The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ...
There are places where dark matter seems to be a small component or totally absent. Globular clusters show no evidence that they contain dark matter, though their orbital interactions with galaxies do show evidence for galactic dark matter. For some time, measurements of the velocity profile of stars seemed to indicate concentration of dark matter in the disk of the Milky Way galaxy, however, now it seems that the high concentration of baryonic matter in the disk of the galaxy (especially in the interstellar medium) can account for this motion. Galaxy mass profiles are thought to look very different from the light profiles. The typical model for dark matter galaxies is a smooth, spherical distribution in virialized halos. Such would have to be the case to avoid small-scale (stellar) dynamical effects. Recent research reported in January 2006 from the University of Massachusetts, Amherst would explain the previously mysterious warp in the disk of the Milky Way by the interaction of the Large and Small Magellanic Clouds and the predicted 20 fold increase in mass of the Milky Way taking into account dark matter. A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ...
It has been proposed below that Disc (galaxy) be renamed and moved to galactic disc. ...
For other uses, see Milky Way (disambiguation). ...
The center of the UMass Amherst campus. ...
The Large Magellanic Cloud (LMC) is a nearby satellite galaxy of our own galaxy, the Milky Way. ...
The Small Magellanic Cloud (SMC) is a dwarf galaxy[1] in orbit around the Milky Way Galaxy. ...
In 2005, astronomers from Cardiff University claimed to discover a galaxy made almost entirely of dark matter, 50 million light years away in the Virgo Cluster, which was named VIRGOHI21.[9] Unusually, VIRGOHI21 does not appear to contain any visible stars: it was seen with radio frequency observations of hydrogen. Based on rotation profiles, the scientists estimate that this object contains approximately 1000 times more dark matter than hydrogen and has a total mass of about 1/10th that of the Milky Way Galaxy we live in. For comparison, the Milky Way is believed to have roughly 10 times as much dark matter as ordinary matter. Models of the Big Bang and structure formation have suggested that such dark galaxies should be very common in the universe, but none had previously been detected. If the existence of this dark galaxy is confirmed, it provides strong evidence for the theory of galaxy formation and poses problems for alternative explanations of dark matter. The main building of Cardiff University Wikimedia Commons has media related to: Cardiff University Cardiff University (Welsh: Prifysgol Caerdydd) is a leading university located in the civic centre of Cardiff, Wales. ...
For other uses, see Galaxy (disambiguation). ...
A sky field near some of the brighter galaxies in the Virgo cluster. ...
VIRGOHI21 is a dark matter halo in the Virgo cluster. ...
The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos; or simply the Galaxy) is a barred spiral galaxy in the Local Group, and has special significance to humanity as the location of the solar system, which is located near the Orion...
For other uses, see Big Bang (disambiguation). ...
This box: In physical cosmology, the term large-scale structure refers to the characterization of observable distributions of matter and light on the largest scales (typically on the order of billions of light-years). ...
Recently too there is evidence that there are 10 to 100 times fewer small galaxies than permitted by what the dark matter theory of galaxy formation predicts. There are also a small number of galaxies, like NGC 3379 whose measured orbital velocity of its gas clouds, show that it contains almost no dark matter at all.[10] Elliptical Galaxy M105 (also known as Messier Object 105, Messier 105, M105, or NGC 3379) is an elliptical galaxy in the Leo constellation. ...
[edit] Missing matter in clusters of galaxies Dark matter affects galaxy clusters as well. X-ray measurements of hot intracluster gas correspond closely to Zwicky's observations of mass-to-light ratios for large clusters of nearly 10 to 1. Many of the experiments of the Chandra X-ray Observatory use this technique to independently determine the mass of clusters. Download high resolution version (750x938, 126 KB)Gravitational lensing. ...
Download high resolution version (750x938, 126 KB)Gravitational lensing. ...
The Hubble Space Telescope (HST; also known colloquially as the Hubble or just Hubble) is a space telescope that was carried into Earth orbit by the Space Shuttle in April 1990. ...
Abell 1689 is a galaxy cluster in the constellation Virgo. ...
For other uses, see NASA (disambiguation). ...
This article is about the European Space Agency. ...
Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...
In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...
Intergalactic space is the physical space between galaxies. ...
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. ...
The galaxy cluster Abell 2029 is composed of thousands of galaxies enveloped in a cloud of hot gas, and an amount of dark matter equivalent to more than 1014 Suns. At the center of this cluster is an enormous, elliptically shaped galaxy that is thought to have been formed from the mergers of many smaller galaxies.[11] The measured orbital velocities of galaxies within galactic clusters have been found to be consistent with dark matter observations. Abell 2029 is a large cluster of galaxies a billion light years away in the constellation Serpens, close to its boundary with Virgo [1]. The central galaxy (IC 1101) is perhaps the largest known, with estimates ranging from 5. ...
Another important tool for future dark matter observations is gravitational lensing. Lensing relies on the effects of general relativity to predict masses without relying on dynamics, and so is a completely independent means of measuring the dark matter. Strong lensing, the observed distortion of background galaxies into arcs when the light passes through a gravitational lens, has been observed around a few distant clusters including Abell 1689 (pictured right). By measuring the distortion geometry, the mass of the cluster causing the phenomena can be obtained. In the dozens of cases where this has been done, the mass-to-light ratios obtained correspond to the dynamical dark matter measurements of clusters. A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ...
For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ...
Abell 1689 is a galaxy cluster in the constellation Virgo. ...
Perhaps more convincing, a technique has been developed over the last 10 years called weak gravitational lensing, which looks at minute distortions of galaxies observed in vast galaxy surveys due to foreground objects through statistical analyses. By examining the apparent shear deformation of the adjacent background galaxies, astrophysicists can characterize the mean distribution of dark matter by statistical means and have found mass-to-light ratios that correspond to dark matter densities predicted by other large-scale structure measurements. The correspondence of the two gravitational lens techniques to other dark matter measurements has convinced almost all astrophysicists that dark matter actually exists as a major component of the universe's composition. This article is in need of attention from an expert on the subject. ...
In astronomy, a redshift survey is a survey of a section of the sky to measure the redshift of astronomical objects. ...
[edit] Structure formation -
Dark matter is crucial to the Big Bang model of cosmology as a component which corresponds directly to measurements of the parameters associated with Friedmann cosmology solutions to general relativity. In particular, measurements of the cosmic microwave background anisotropies correspond to a cosmology where much of the matter interacts with photons more weakly than the known forces that couple light interactions to baryonic matter. Likewise, a significant amount of non-baryonic, cold matter is necessary to explain the large-scale structure of the universe. It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ...
For other uses, see Big Bang (disambiguation). ...
A pie chart indicating the proportional composition of different energy-density components of the universe. ...
The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. ...
For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ...
WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ...
In physics, the photon (from Greek φως, phÅs, meaning light) is the quantum of the electromagnetic field; for instance, light. ...
A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ...
Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ...
This box: In physical cosmology, the term large-scale structure refers to the characterization of observable distributions of matter and light on the largest scales (typically on the order of billions of light-years). ...
Observations suggest that structure formation in the universe proceeds hierarchically, with the smallest structures collapsing first and followed by galaxies and then clusters of galaxies. As the structures collapse in the evolving universe, they begin to "light up" as the baryonic matter heats up through gravitational contraction and the object approaches hydrostatic pressure balance. Ordinary baryonic matter had too high a temperature, and too much pressure left over from the Big Bang to collapse and form smaller structures, such as stars, via the Jeans instability. Dark matter acts as a compactor of structure. This model not only corresponds with statistical surveying of the visible structure in the universe but also corresponds precisely to the dark matter predictions of the cosmic microwave background. It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ...
Hydrostatic equilibrium occurs when compression due to gravity is balanced by a pressure gradient which creates a pressure gradient force in the opposite direction. ...
Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ...
It has been suggested that Jeans mass be merged into this article or section. ...
This bottom up model of structure formation requires something like cold dark matter to succeed. Large computer simulations of billions of dark matter particles have been used to confirm that the cold dark matter model of structure formation is consistent with the structures observed in the universe through galaxy surveys, such as the Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey, as well as observations of the Lyman-alpha forest. These studies have been crucial in constructing the Lambda-CDM model which measures the cosmological parameters, including the fraction of the universe made up of baryons and dark matter. SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ...
In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Gurvey), or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory in the 1990s. ...
In astronomical spectroscopy, the Lyman alpha forest is the sum of absorption lines seen in spectra of distant galaxies and quasars, beginning from the Lyman alpha line at 121. ...
A pie chart indicating the proportional composition of different energy-density components of the universe. ...
[edit] Gravitational Lensing and the Bullet Cluster Gravitational lensing can be used to directly map the total distribution of mass, including both dark matter and visible material.[12] In most regions of the universe, dark matter and visible material are found together,[13] as expected because of their mutual gravitational attraction. This article or section is in need of attention from an expert on the subject. ...
However, the collision of two galaxy clusters around 150 million years ago appears to have caused the separation of baryonic and dark matter in what is now called the Bullet Cluster. This separation of the different forms of matter has provided an opportunity to test for the presence of dark matter. Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...
The Bullet cluster (1E 0657-56) consists of two colliding clusters of galaxies. ...
Researchers mapped the distribution of mass using measurements of gravitational lensing, and compared it to X-ray maps showing hot (107–108 Kelvin[7]) plasma, thought to constitute the large majority of ordinary matter in the clusters. The hot gases in the two clusters collided and slowed down: they now lie close to the point of impact. Conversely, the dark matter and most of the stars do not collide, and so are now separated from the X-ray emitting gas.[7] In several hundred million years, gravitational attraction between the different concentrations of matter is expected to pull them back together, reproducing the usual configuration. For other uses, see Kelvin (disambiguation). ...
[edit] Dark matter composition Although dark matter was detected by its gravitational lensing in August 2006,[14] many aspects of dark matter remain speculative. The DAMA/NaI experiment and its successor DAMA/LIBRA have claimed to directly detect dark matter passing through the Earth, though most scientists remain skeptical since negative results of other experiments are (almost) incompatible with the DAMA results if dark matter consists of neutralinos. Image File history File links No higher resolution available. ...
This is a list of some of the unsolved problems in physics. ...
This article or section is in need of attention from an expert on the subject. ...
This article or section is in need of attention from an expert on the subject. ...
The DAMA/NaI experiment [1] was designed to detect dark matter using the direct detection technique. ...
In particle physics, the neutralino is a hypothetical particle and part of the doubling of the menagerie of particles predicted by supersymmetric theories. ...
Data from a number of lines of evidence, including galaxy rotation curves, gravitational lensing, structure formation, and the fraction of baryons in clusters and the cluster abundance combined with independent evidence for the baryon density, indicate that 85-90% of the mass in the universe does not interact with the electromagnetic force. This "dark matter" is evident through its gravitational effect. Several categories of dark matter have been postulated. 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. ...
Davis et al wrote in 1985: Hot dark matter is a form of dark matter, which consists of particles that travel with relativistic velocities. ...
In physics, ultrarelativistic is said of a particle when its speed is very close to the speed of light , such that its total energy is almost completely due to its momentum (), and thus can be approximated by . ...
Warm dark matter (WDM) is theorized to have properties which are intermediate between those of hot dark matter and cold dark matter. ...
Cold dark matter (or CDM) is a refinement of the big bang theory, as well as being one possible variation of the more generic Dark Matter theory. ...
Candidate particles can be grouped into three categories on the basis of their effect on the fluctuation spectrum (Bond et al 1983). If the dark matter is composed of abundant light particles which remain relativistic until shortly before recombination, then it may be termed "hot". The best candidate for hot dark matter is a neutrino [..] A second possibility is for the dark matter particles to interact more weakly than neutrinos, to be less abundant, and to have a mass of order 1eV. Such particles are termed "warm dark matter", because they have lower thermal velocities than massive neutrinos [..] there are at present few candidate particles which fit this description. Gravitinos and photinos have been suggested (Pagels and Primack 1982; Bond, Szalay and Turner 1982) [..] Any particles which became nonrelativistic very early, and so were able to diffuse a negligible distance, are termed "cold" dark matter (CDM). There are many candidates for CDM including supersymmetric particles[18] Hot dark matter consists of particles that travel with relativistic velocities. One kind of hot dark matter is known, the neutrino. Neutrinos have a very small mass, do not interact via either the electromagnetic or the strong nuclear force and are therefore very difficult to detect. This is what makes them appealing as dark matter. However, bounds on neutrinos indicate that ordinary neutrinos make only a small contribution to the density of dark matter. For a generally accessible and less technical introduction to the topic, see Introduction to special relativity. ...
For other uses, see Neutrino (disambiguation). ...
Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ...
The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ...
Hot dark matter cannot explain how individual galaxies formed from the Big Bang. The microwave background radiation as measured by the COBE and WMAP satellites, while incredibly smooth, indicates that matter has clumped on very small scales. Fast moving particles, however, cannot clump together on such small scales and, in fact, suppress the clumping of other matter. Hot dark matter, while it certainly exists in our universe in the form of neutrinos, is therefore only part of the story. WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ...
The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ...
Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ...
 Estimated distribution of dark matter and dark energy in the universe The Concordance Model requires that, to explain structure in the universe, it is necessary to invoke cold (non-relativistic) dark matter. Large masses, like galaxy-sized black holes can be ruled out on the basis of gravitational lensing data. Possibilities involving normal baryonic matter include brown dwarfs or perhaps small, dense chunks of heavy elements; such objects are known as massive compact halo objects, or "MACHOs". However, studies of big bang nucleosynthesis have convinced most scientists that baryonic matter such as MACHOs cannot be more than a small fraction of the total dark matter. Image File history File links No higher resolution available. ...
Image File history File links No higher resolution available. ...
A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ...
Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ...
This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ...
Massive compact halo object, or MACHO, is a general name for any kind of astronomical body that might explain the apparent presence of dark matter in galaxy halos. ...
In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ...
Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ...
At present, the most common view is that dark matter is primarily non-baryonic, made of one or more elementary particles other than the usual electrons, protons, neutrons, and known neutrinos. The most commonly proposed particles are axions, sterile neutrinos, and WIMPs (Weakly Interacting Massive Particles, including neutralinos). None of these are part of the standard model of particle physics, but they can arise in extensions to the standard model. Many supersymmetric models naturally give rise to stable WIMPs in the form of neutralinos. Heavy, sterile neutrinos exist in extensions to the standard model that explain the small neutrino mass through the seesaw mechanism. In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called Greek barys, meaning heavy, as they are heavier than the other main groups of particles. ...
For other uses, see Electron (disambiguation). ...
For other uses, see Proton (disambiguation). ...
This article or section does not adequately cite its references or sources. ...
The neutrino is an elementary particle. ...
For other uses, see Axion (disambiguation). ...
A sterile neutrino is an neutrino that does not interact via any of the fundamental interactions of the Standard Model. ...
In particle physics, the neutralino is a hypothetical particle and part of the doubling of the menagerie of particles predicted by supersymmetric theories. ...
The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ...
Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...
This article or section is in need of attention from an expert on the subject. ...
In particle physics, the neutralino is a hypothetical particle and part of the doubling of the menagerie of particles predicted by supersymmetric theories. ...
The neutrino is an elementary particle. ...
In theoretical physics, the seesaw mechanism is a mechanism to generate very small numbers from reasonable numbers and very large numbers. ...
[edit] Detection of dark matter These cosmological models predict that if WIMPs are what make up dark matter, trillions must pass through the Earth each second. Despite a number of attempts to find these WIMPs, none have yet been confirmedly found.
Experimental searches for these dark matter candidates have been conducted and are ongoing. These efforts can be divided into two broad classes: direct detection, in which the dark matter particles are observed in a detector; and indirect detection, which looks for the products of dark matter annihilations. Dark matter detection experiments have ruled out some WIMP and axion models. There are also several experiments claiming positive evidence for dark matter detection, such as DAMA/NaI, DAMA/LIBRA[19] and EGRET, but these are so far unconfirmed and difficult to reconcile with the negative results of other experiments. Several searches for dark matter are currently underway, including the Cryogenic Dark Matter Search in the Soudan mine, the XENON, DAMA/LIBRA and CRESST experiments at Gran Sasso and the ZEPLIN project at the Boulby Underground Laboratory (UK), and many new technologies are under development, such as the ArDM experiment. For other uses, see Axion (disambiguation). ...
The DAMA/NaI experiment [1] was designed to detect dark matter using the direct detection technique. ...
The sky as seen in high-energy gamma rays The Energetic Gamma Ray Experiment Telescope (EGRET) was one of the four scientific instruments on NASAs Compton Gamma Ray Observatory satellite. ...
The Cryogenic Dark Matter Search (CDMS) is an experiment designed to directly detect particle dark matter in the form of WIMPs. ...
The Soudan Underground Mine is described as Minnesotas oldest, deepest, and richest iron mine. ...
General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Standard atomic weight 131. ...
The Laboratori Nazionali del Gran Sasso is a particle physics laboratory of the INFN, situated near the Gran Sasso mountain in Italy, between the towns of LAquila and Teramo. ...
ArDM (Argon Dark Matter) is a particle physics experiment based on a liquid argon detector, aiming at measuring signals from WIMPs (Weakly Interacting Massive Particles), which probably constitute the Dark Matter in the universe. ...
One possible alternative approach to the detection of WIMPs in nature is to produce them in the laboratory. Experiments with the Large Hadron Collider near Geneva may be able to detect WIMPs. Because a WIMP only has negligible interactions with matter, it can be detected as missing energy and momentum. It is also possible that dark matter consists of very heavy hidden sector particles which only interact with ordinary matter via gravity. , The Large Hadron Collider (LHC) is a particle accelerator and Hadron collider located at CERN, near Geneva, Switzerland. ...
For other uses, see Geneva (disambiguation). ...
In particle physics, the term hidden sector refers to the collection of yet-unobserved quantum fields and the corresponding hypothetical particles that do not directly interact via the forces of the Standard Model i. ...
The Cryogenic Dark Matter Search, in the Soudan Mine in Minnesota aims to detect the heat generated when ultracold germanium and silicon crystals are struck by a WIMP. The Gran Sasso National Laboratory at L'Aquila, in Italy, use xenon to measure the flash of light that occurs on those rare occasions when a WIMP strikes a xenon nucleus. The results from April 2007, using 15 kg of liquid and gaseous xenon, failed to detect any, and in March 2008 the team started again using 150 kg of the material. General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Standard atomic weight 72. ...
Not to be confused with Silicone. ...
Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ...
General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Standard atomic weight 131. ...
The GLAST space telescope, launched June 11, 2008, searching gammawave events, may also detect WIMPs. WIMP supersymmetric particle and antiparticle collisions should release a pair of detectable gamma waves. The number of events detected will show to what extent WIMPs comprise dark matter. The Gamma-ray Large Area Space Telescope, or GLAST, is a future space-based gamma-ray telescope, designed to explore the high-energy Universe. ...
With all these experiments together, scientists are becoming confident that WIMPs will be discovered in the near future. But some scientists are beginning to think that dark matter is composed of many different candidates.[20] WIMPs may thus only be a part of the solution.
[edit] Alternative explanations
[edit] Modifications of gravity A proposed alternative to physical dark matter particles has been to suppose that the observed inconsistencies are due to an incomplete understanding of gravitation. To explain the observations, the gravitational force has to become stronger than the Newtonian approximation at great distances or in weak fields. One of the proposed models is Modified Newtonian Dynamics (MOND), which adjusts Newton's laws at small acceleration. However, constructing a relativistic MOND theory has been troublesome, and it is not clear how the theory can be reconciled with gravitational lensing measurements of the deflection of light around galaxies. The leading relativistic MOND theory, proposed by Jacob Bekenstein in 2004 is called TeVeS for Tensor-Vector-Scalar and solves many of the problems of earlier attempts. However, a study in August 2006 reported an observation of a pair of colliding galaxy clusters whose behavior, it was claimed, was not compatible with any current modified gravity theories.[21] Gravity redirects here. ...
In physics, Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newtons Second Law of Dynamics, to explain the galaxy rotation problem. ...
Newtons laws of motion are the three scientific laws which Isaac Newton discovered concerning the behaviour of moving bodies. ...
-1...
A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ...
Jacob David Bekenstein (born May 1, 1947) is a physicist who has contributed to the foundation of black hole thermodynamics and to other aspects of the connections between information and gravitation. ...
Tevet (טֵבֵת, Standard Hebrew Tevet, Tiberian Hebrew Ṭēḇēṯ: from Akkadian ṭebētu) is the fourth month of the ecclesiastical year and the tenth month of the civil year on the Hebrew calendar. ...
In 2007, astronomer John W. Moffatt proposed a theory of modified gravity (MOG) based on the Nonsymmetric Gravitational Theory (NGT) that accounts for the behavior of colliding galaxies.[22] John Moffat is a Professor Emeritus in physics at the University of Toronto. ...
Nonsymmetric Gravitational Theory is a modification of Einsteins theory of General Relativity that tries to explain the mystery of Dark Matter. ...
[edit] Quantum mechanical explanations In another class of theories one attempts to reconcile gravitation with quantum mechanics and obtains corrections to the conventional gravitational interaction. In scalar-tensor theories, scalar fields like the Higgs field couple to the curvature given through the Riemann tensor or its traces. In many of such theories, the scalar field equals the inflaton field, which is needed to explain the inflation of the universe after the Big Bang, as the dominating factor of the quintessence or Dark Energy. Using an approach based on the exact renormalization group, M. Reuter and H. Weyer have shown[23] that Newton's constant and the cosmological constant can be scalar functions on spacetime if one associates renormalization scales to the points of spacetime. Some M-Theory cosmologists also propose that multi-dimensional forces from outside the visible universe have gravitational effects on the visible universe meaning that dark matter is not necessary for a unified theory of cosmology. Gravity redirects here. ...
For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ...
This article is in need of attention from an expert on the subject. ...
See scalar for an account of the broader concept also used in mathematics and computer science. ...
The term Higgs appears in: Higgs boson, theoretical elementary particle Peter Higgs, physicist Higgs Laws of Convergence Simon Higgs, author of the Higgs Laws This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. ...
Bernhard Riemann. ...
The inflaton is the generic name of the unidentified scalar field (and its associated particle), that may be responsible for an episode of inflation in the very early universe. ...
For other uses, see Big Bang (disambiguation). ...
In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an a |
