• • • Dark matter is a hypothetical type of distinct from (ordinary matter such as and ) and. Dark matter has never been directly observed; however, its existence would explain a number of otherwise puzzling astronomical observations. The name refers to the fact that it does not emit or interact with observable, such as, and is thus invisible to the entire. Although dark matter has not been directly observed, its existence and properties are inferred from its gravitational effects such as the motions of baryonic matter,, its influence on the universe's, on the formation of, and its effects on the. The indicates that the total of the universe contains 4.9%, 26.8% dark matter and 68.3%.

In 1968, Part I of Detection, Estimation, and Modulation Theory [VT681 was pub- lished. It turned out to be a reasonably successful book that has been widely used by several generations of engineers. There were thirty printings, but the last printing was in 1996. Volumes II and III ([VT7 1 a], [VT7 1 b]) were published in 197 1. Manitou Mlt 735 Operators Manual Document about Manitou Mlt 735 Operators Manual is available on print and digital edition. This pdf ebook is one of digital edition.

Thus, dark matter constitutes 84.5% of total, while dark energy plus dark matter constitute 95.1% of total mass–energy content. The great majority of ordinary matter in the universe is also unseen. Visible stars and gas inside galaxies and clusters account for less than 10% of the ordinary matter contribution to the mass-energy density of the universe. The most widely accepted hypothesis on the form for dark matter is that it is composed of (WIMPs) that interact only through gravity and the. The dark matter hypothesis plays a central role in current modeling of cosmic,, and on explanations of the observed in the (CMB).

All these lines of evidence suggest that galaxies, galaxy clusters, and the universe as a whole contain far more matter than that which is observable via electromagnetic signals. Many experiments to detect proposed dark matter particles through non-gravitational means are under way; however, no dark matter particle has been conclusively identified. Although the existence of dark matter is generally accepted by most of the astronomical community, a minority of astronomers, motivated by the lack of conclusive identification of dark matter, or by observations that don't fit the model, argue for various modifications of the standard laws of, such as,, and that attempt to account for the observations without invoking additional matter. See also: In standard cosmology, matter is anything whose energy density scales with the inverse cube of the, i.e. This is in contrast to radiation, which scales to the inverse fourth power of the scale factor ρ ∝ a −4, and dark energy, which is unaffected ρ ∝ a 0. This can be understood intuitively: for an ordinary particle in a square box, doubling the length of the sides of the box decreases the density (and hence energy density) by a factor of eight (2 3). For radiation, the decrease in energy density is greater, because an increase in spatial distance also causes a redshift.

Dark energy, as an intrinsic property of space, has a constant energy density regardless of the volume under consideration. Dark matter is that component of the universe which is not ordinary matter, but still obeys ρ ∝ a −3. Observational evidence [ ].

Comparison of rotating disc galaxies in the distant Universe and the present day. The imaginary galaxy on the left is in the nearby Universe and the stars in its outer parts are orbiting rapidly due to the presence of large amounts of dark matter around the central regions. On the other hand, the galaxy at the right, which is in the distant Universe, and seen as it was about ten billion years ago, is rotating more slowly in its outer parts as dark matter is more diffuse. The size of the difference is exaggerated in this schematic view to make the effect clearer. The distribution of dark matter is shown in red. The arms of rotate around the galactic centre.

The luminous mass density of a spiral galaxy decreases as one goes from the centre to the outskirts. If luminous mass were all the matter, then we can model the galaxy as a point mass in the centre and test masses orbiting around it (similar to the ). From, we expect that the rotation velocities will decrease with distance from the centre, similar to our solar system. This is not observed.

Instead, the galaxy rotation curve remains flat as distant from the centre as the data is available. If we assume the validity of Kepler's laws, then the obvious way to resolve this discrepancy is to conclude that the mass distribution in spiral galaxies is not similar to that of the solar system. In particular, there is a lot of non-luminous matter in the outskirts of the galaxy ('dark matter'). Velocity dispersions [ ]. Main article: Stars in bound systems must obey the. The theorem, together with the measured velocity distribution, can be used to measure the mass distribution in a bound system, such as elliptical galaxies or globular clusters. With some exceptions, velocity dispersion estimates of elliptical galaxies do not match the predicted velocity dispersion from the observed mass distribution, even assuming complicated distributions of stellar orbits.

As with galaxy rotation curves, the obvious way to resolve the discrepancy is to postulate the existence of non-luminous matter. Galaxy clusters [ ]. Strong gravitational lensing as observed by the in indicates the presence of dark matter—enlarge the image to see the lensing arcs.

Are particularly important for dark matter studies since their masses can be estimated in three independent ways: • From the scatter in radial velocities of the galaxies within clusters • From emitted by hot gas in the clusters. From the X-ray energy spectrum and flux, the gas temperature and density can be estimated, hence giving the pressure; assuming pressure and gravity balance determines the cluster's mass profile. • (usually of more distant galaxies) can measure cluster masses without relying on observations of dynamics (e.g., velocity). Generally, these three methods are in reasonable agreement that dark matter outweighs visible matter by approximately 5 to 1 [ ]. Gravitational lensing [ ] One of the consequences of is that massive objects (such as a ) lying between a more distant source (such as a ) and an observer should act as a lens to bend the light from this source. The more massive an object, the more lensing is observed.

Strong lensing is the observed distortion of background galaxies into arcs when their light passes through such a gravitational lens. It has been observed around many distant clusters including. By measuring the distortion geometry, the mass of the intervening cluster 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.

Lensing can lead to multiple copies of an image. By analyzing the distribution of multiple image copies, scientists have been able to deduce and map the distribution of dark matter around the galaxy cluster. Investigates minute distortions of galaxies, using statistical analyses from vast.

By examining the apparent shear deformation of the adjacent background galaxies, the mean distribution of dark matter can be characterized. The mass-to-light ratios correspond to dark matter densities predicted by other large-scale structure measurements.

Cosmic microwave background [ ]. The cosmic microwave background by Although both dark matter and ordinary matter are 'matter', they do not behave in the same way. In particular, in the early universe, ordinary matter was ionized and interacted strongly with radiation via. Dark matter does not interact directly with radiation, but it does affect the CMB by its gravitational potential (mainly on large scales), and by its effects on the density and velocity of ordinary matter. Ordinary and dark matter perturbations therefore evolve differently with time, and leave different imprints on the cosmic microwave background (CMB). The cosmic microwave background is very close to a perfect blackbody, but contains very small temperature anisotropies of a few parts in 100,000.

A sky map of anisotropies can be decomposed into an angular power spectrum, which is observed to contain a series of 'acoustic peaks' at near-equal spacing but different heights. The series of peaks can be predicted for any assumed set of cosmological parameters by modern computer codes such as CMBFast and CAMB, and matching theory to data therefore constrains cosmological parameters. The first peak mostly shows the density of baryonic matter, while the third peak relates mostly to the density of dark matter, measuring the density of matter and the density of atoms.

The CMB anisotropy was first discovered by in 1992, though this had too coarse resolution to detect the acoustic peaks. After the discovery of the first acoustic peak by the balloon-borne experiment in 2000, the power spectrum was precisely observed by in 2003-12, and even more precisely by the in 2013-15. The results support the Lambda-CDM model. The observed CMB angular power spectrum provides powerful evidence in support of dark matter, as its precise structure is well fitted by the but difficult to reproduce with any competing model such as. Structure formation [ ]. 3D map of the large-scale distribution of dark matter, reconstructed from measurements of with the.

Structure formation refers to the period after the Big Bang when density perturbations collapsed to form stars, galaxies, and clusters. Prior to structure formation, the to general relativity describe a homogeneous universe. Later, small anisotropies gradually grew and condensed the homogeneous universe into stars, galaxies and larger structures. Ordinary matter is affected by radiation, which is the dominant element of the universe at very early times. As a result, its density perturbations are washed out and unable to condense into structure. If there were only ordinary matter in the universe, there would not have been enough time for density perturbations to grow into the galaxies and clusters that we see today.

Dark matter provides a solution to this problem because it is unaffected by radiation. Therefore, its density perturbations can grow first. The resulting gravitational potential acts as an attractive for ordinary matter collapsing later, speeding up the structure formation process.

Type Ia supernova distance measurements [ ]. Main articles: and Type Ia can be used as ' to measure extragalactic distances, which can in turn be used to measure how fast the universe has expanded in the past.

The data indicates that the universe is expanding at an accelerating rate, the cause of which is usually ascribed to. Since observations indicate the universe is almost flat, we expect the total energy density of everything in the universe to sum to 1 (Ω tot ~ 1).

The measured dark energy density is Ω Λ = ~0.690; the observed ordinary (baryonic) matter energy density is Ω b = ~0.0482 and the energy density of radiation is negligible. This leaves a missing Ω dm = ~0.258 that nonetheless behaves like matter (see technical definition section above) – dark matter. Sky surveys and baryon acoustic oscillations [ ]. Main article: Baryon acoustic oscillations (BAO) are regular, periodic fluctuations in the density of the visible matter (normal matter) of the universe. These are predicted to arise in the Lambda-CDM model due to the early universe's acoustic oscillations in the photon-baryon fluid and can be observed in the cosmic microwave background angular power spectrum. BAOs set up a preferred length scale for baryons. As the dark matter and baryons clumped together after recombination, the effect is much weaker in the galaxy distribution in the nearby universe, but is detectable as a subtle (~ 1 percent) preference for pairs of galaxies to be separated by 147 Mpc, compared to those separated by 130 or 160 Mpc.

This feature was predicted theoretically in the 1990s and then discovered in 2005, in two large galaxy redshift surveys, the and the. Combining the CMB observations with BAO measurements from galaxy provides a precise estimate of the and the average matter density in the Universe. The results support the Lambda-CDM model.

Redshift-space distortions [ ] Large galaxy may be used to make a three-dimensional map of the galaxy distribution. These maps are slightly distorted because distances are estimated from observed; the redshift contains a contribution from the galaxy's so-called peculiar velocity in addition to the dominant Hubble expansion term. On average, superclusters are expanding but more slowly than the cosmic mean due to their gravity, while voids are expanding faster than average. In a redshift map, galaxies in front of a supercluster have excess radial velocities towards it and have redshifts slightly higher than their distance would imply, while galaxies behind the supercluster have redshifts slightly low for their distance.

This effect causes superclusters to appear 'squashed' in the radial direction, and likewise voids are 'stretched'; angular positions are unaffected. The effect is not detectable for any one structure since the true shape is not known, but can be measured by averaging over many structures assuming we are not at a special location in the Universe. The effect was predicted quantitatively by Nick Kaiser in 1987, and first decisively measured in 2001 by the. Results are in agreement with the. Lyman-alpha forest [ ]. What is dark matter? How is it generated?

Is it related to? Dark matter can refer to any substance which interacts predominantly via gravity with visible matter (e.g. Stars and planets). Hence in principle it need not be composed of a new type of fundamental particle but could, at least in part, be made up of standard baryonic matter, such as protons or electrons. However, for the reasons outlined below, most scientists consider the dark matter to be dominated by a non-baryonic component, which is likely composed of a currently unknown fundamental particle (or similar exotic state). Not to be confused with. ( and ) make up ordinary stars and planets.

However, baryonic matter also encompasses less common,, faint old and, collectively known as (MACHOs). This ordinary, but hard to see, matter could explain dark matter.

However multiple lines of evidence suggest the majority of dark matter is not made of baryons: • Sufficient diffuse, baryonic gas or dust would be visible when backlit by stars. • The theory of predicts the observed. If there are more baryons, then there should also be more helium, lithium and heavier elements synthesized during the Big Bang. Agreement with observed abundances requires that baryonic matter makes up between 4–5% of the universe's. In contrast, and other observations indicate that the total matter density is about 30% of the critical density.

• Astronomical searches for in the found that at most a small fraction of the dark matter may be in dark, compact, conventional objects (MACHOs, etc.); the excluded range of object masses is from half the Earth's mass up to 30 solar masses, which covers nearly all the plausible candidates. • Detailed analysis of the small irregularities (anisotropies) in the. Observations by and indicate that around five-sixths of the total matter is in a form that interacts significantly with ordinary matter or only through gravitational effects. Non-baryonic matter [ ] Candidates for nonbaryonic dark matter are hypothetical particles such as, or (e.g.

The three neutrino types already observed are indeed abundant, and “dark”, and matter, but because their individual masses – however uncertain they may be – are almost certainly tiny, they can only supply a small fraction of dark matter, due to limits derived from and high- galaxies. Unlike baryonic matter, nonbaryonic matter did not contribute to the formation of the in the early universe (') and so its presence is revealed only via its gravitational effects.

In addition, if the particles of which it is composed are supersymmetric, they can undergo interactions with themselves, possibly resulting in observable by-products such as and neutrinos ('indirect detection'). Classification of dark matter: cold, warm or hot [ ] Dark matter can be divided into cold, warm and hot categories. These categories refer to velocity rather than an actual temperature, indicating how far corresponding objects moved due to random motions in the early universe, before they slowed due to cosmic expansion – this is an important distance called the 'free streaming length' (FSL).

Primordial density fluctuations smaller than this length get washed out as particles spread from overdense to underdense regions, while larger fluctuations are unaffected; therefore this length sets a minimum scale for later structure formation. The categories are set with respect to the size of a (an object that later evolves into a dwarf galaxy): dark matter particles are classified as cold, warm, or hot according as their FSL; much smaller (cold), similar (warm), or much larger (hot) than a protogalaxy. Mixtures of the above are also possible: a theory of was popular in the mid-1990s, but was rejected following the discovery of. [ ] Cold dark matter leads to a 'bottom-up' formation of structure while hot dark matter would result in a 'top-down' formation scenario; the latter is excluded by high-redshift galaxy observations. Alternative definitions [ ] These categories also correspond to effects and the interval following the Big Bang at which each type became non-relativistic. Wrote in 1985: “ Candidate particles can be grouped into three categories on the basis of their effect on the (Bond et al.

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 1 keV. 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. And 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.

” Another approximate dividing line is that 'warm' dark matter became non-relativistic when the universe was approximately 1 year old and 1 millionth of its present size and in the (photons and neutrinos), with a photon temperature 2.7 million K. Standard physical cosmology gives the size as 2 ct (speed of light multiplied by time) in the radiation-dominated era, thus 2 light-years. A region of this size would expand to 2 million light years today (absent structure formation). The actual FSL is roughly 5 times the above length, since it continues to grow slowly as particle velocities decrease inversely with the scale factor after they become non-relativistic. In this example the FSL would correspond to 10 million light-years or 3 Mpc today, around the size containing an average large galaxy.

The 2.7 million K photon temperature gives a typical photon energy of 250 electron-volts, thereby setting a typical mass scale for 'warm' dark matter: particles much more massive than this, such as GeV – TeV mass, would become non-relativistic much earlier than 1 year after the Big Bang and thus have FSLs much smaller than a protogalaxy, making them 'cold'. Conversely, much lighter particles, such as neutrinos with masses of only a few eV, have FSLs much larger than a protogalaxy, thus qualifying them as 'hot'. Cold dark matter [ ]. Main article: 'Cold' dark matter offers the simplest explanation for most cosmological observations. It is dark matter composed of constituents with an FSL much smaller than a protogalaxy. This is the focus for dark matter research, as hot dark matter does not seem to be capable of supporting galaxy or galaxy cluster formation, and most particle candidates slowed early. The constituents of 'cold' dark matter are unknown.

Possibilities range from large objects like MACHOs (such as black holes ) or (such as clusters of brown dwarfs), to new particles such as and. Studies of and gravitational lensing convinced most cosmologists that MACHOs cannot make up more than a small fraction of dark matter. According to A. The only really plausible dark-matter candidates are new particles.' The 1997 experiment and its successor in 2013, claimed to directly detect dark matter particles passing through the Earth, but many researchers remain skeptical, as negative results from similar experiments seem incompatible with the DAMA results. Many models offer dark matter candidates in the form of the WIMPy (LSP).

Separately, heavy sterile neutrinos exist in non-supersymmetric extensions to the that explain the small through the. Warm dark matter [ ]. Main article: 'Warm' dark matter refers to particles with an FSL comparable to the size of a protogalaxy. Predictions based on warm dark matter are similar to those for cold dark matter on large scales, but with less small-scale density perturbations.

This reduces the predicted abundance of dwarf galaxies and may lead to lower density of dark matter in the central parts of large galaxies; some researchers consider this to be a better fit to observations. A challenge for this model is the lack of particle candidates with the required mass ~ 300 eV to 3000 eV. [ ] No known particles can be categorized as 'warm' dark matter.

A postulated candidate is the: a heavier, slower form of neutrino that does not interact through the, unlike other neutrinos. Some modified gravity theories, such as, require 'warm' dark matter to make their equations work.

40 Carati Download Ita Gratis. Hot dark matter [ ]. Main article: 'Hot' dark matter consists of particles whose FSL is much larger than the size of a protogalaxy. The qualifies as such particle. They were discovered independently, long before the hunt for dark matter: they were postulated in 1930, and.

Neutrinos' is less than 10 −6 that of an. Neutrinos interact with normal matter only via gravity and the, making them difficult to detect (the weak force only works over a small distance, thus a neutrino triggers a weak force event only if it hits a nucleus head-on). This makes them 'weakly interacting light particles' (WILPs), as opposed to WIMPs.

The three known of neutrinos are the electron, muon, and tau. Their masses are slightly different. Neutrinos oscillate among the flavours as they move. It is hard to determine an exact on the collective average mass of the three neutrinos (or for any of the three individually). For example, if the average neutrino mass were over 50 eV/c 2 (less than 10 −5 of the mass of an electron), the universe would collapse. CMB data and other methods indicate that their average mass probably does not exceed 0.3 eV/c 2.

Thus, observed neutrinos cannot explain dark matter. Because galaxy-size density fluctuations get washed out by free-streaming, 'hot' dark matter implies that the first objects that can form are huge supercluster-size pancakes, which then fragment into galaxies. Show instead that galaxies formed first, followed by clusters and as galaxies clump together. Detection of dark matter particles [ ] If dark matter is made up of sub-atomic particles, then millions, possibly billions, of such particles must pass through every square centimeter of the Earth each second. Many experiments aim to test this hypothesis.

Although are popular search candidates, the Axion Dark Matter eXperiment () searches for. Another candidate is heavy particles that only interact with ordinary matter via gravity. These experiments can be divided into two classes: direct detection experiments, which search for the scattering of dark matter particles off atomic nuclei within a detector; and indirect detection, which look for the products of dark matter particle annihilations or decays. Direct detection [ ]. For more details on this topic, see.

Direct detection experiments aim to observe low-energy recoils (typically a few ) of nuclei induced by interactions with particles of dark matter, which (in theory) are passing through the Earth. After such a recoil the nucleus will emit energy as e.g. Light or, which is then detected by sensitive apparatus. In order to do this effectively it is crucial to maintain a low background, and so such experiments operate deep underground to reduce the interference from.

Examples of underground laboratories which house direct detection experiments include the, the, the underground laboratory at, the, the, the, the and the. These experiments mostly use either cryogenic or noble liquid detector technologies. Cryogenic detectors operating at temperatures below 100mK, detect the heat produced when a particle hits an atom in a crystal absorber such as. Detectors detect produced by a particle collision in liquid. Cryogenic detector experiments include:,,,.

Noble liquid experiments include ZEPLIN,,,,,,, and LUX, the. Both of these techniques focus strongly on their ability to distinguish background particles (which predominantly scatter off electrons) from dark matter particles (that scatter off nuclei). Other experiments include and. Currently there has been no well-established claim of dark matter detection from a direct detection experiment, leading instead to strong upper limits on the mass and interaction cross section with nucleons of such dark matter particles. The and more recent experimental collaborations claim to have detected an annual modulation in the rate of events in their detectors, which they claim is due to dark matter. This results from the expectation that as the Earth orbits the Sun, the velocity of the detector relative to the will vary by a small amount.

This claim is so far unconfirmed and in contradiction with negative results from other experiments such as LUX and SuperCDMS. A special case of direct detection experiments covers those with directional sensitivity. This is a search strategy based on the motion of the Solar System around the. A low pressure makes it possible to access information on recoiling tracks and constrain WIMP-nucleus kinematics. WIMPs coming from the direction in which the Sun is travelling (roughly towards ) may then be separated from background, which should be isotropic. Directional dark matter experiments include,, Newage and MIMAC. Indirect detection [ ].

Video about the potential of dark matter around. (Duration 3:13, also see file description.) Indirect detection experiments search for the products of the self-annihilation or decay of dark matter particles in outer space. For example, in regions of high dark matter density (e.g.

The ) two dark matter particles could to produce or Standard Model particle-antiparticle pairs. Alternatively if the dark matter particle is unstable, it could decay into standard model (or other) particles. These processes could be detected indirectly through an excess of gamma rays, or emanating from high density regions in our galaxy or others. A major difficulty inherent in such searches is that there are various astrophysical sources which can mimic the signal expected from dark matter, and so multiple signals will likely be required for a conclusive discovery.

A few of the dark matter particles passing through the Sun or Earth may scatter off atoms and lose energy. Thus dark matter may accumulate at the center of these bodies, increasing the chance of collision/annihilation.

This could produce a distinctive signal in the form of high-energy. Such a signal would be strong indirect proof of WIMP dark matter. High-energy neutrino telescopes such as, and are searching for this signal. The detection by in of gravitational waves, opens the possibility of observing dark matter in a new way, particularly if it is the form of. Many experimental searches have been undertaken to look for such emission from dark matter annihilation or decay, examples of which follow. The observed more gamma rays in 2008 than expected from the Milky Way, but scientists concluded that this was most likely due to incorrect estimation of the telescope's sensitivity. The is searching for similar gamma rays.

In April 2012, an analysis of previously available data from its instrument produced statistical evidence of a 130 GeV signal in the gamma radiation coming from the center of the Milky Way. WIMP annihilation was seen as the most probable explanation. At higher energies, have set limits on the annihilation of dark matter in dwarf spheroidal galaxies and in clusters of galaxies. The experiment (launched 2006) detected excess. They could be from dark matter annihilation or from.

No excess were observed. In 2013 results from the on the indicated excess high-energy that could be due to dark matter annihilation. Collider searches for dark matter [ ] An alternative approach to the detection of dark matter particles in nature is to produce them in a laboratory. Experiments with the (LHC) may be able to detect dark matter particles produced in collisions of the LHC beams. Because a dark matter particle should have negligible interactions with normal visible matter, it may be detected indirectly as (large amounts of) missing energy and momentum that escape the detectors, provided other (non-negligible) collision products are detected.

Constraints on dark matter also exist from the experiment using a similar principle, but probing the interaction of dark matter particles with electrons rather than quarks. It is important to note that any discovery from collider searches will need to be corroborated by discoveries in the indirect or direct detection sectors, in order to prove that the particle discovered is in fact the dark matter of our Universe. Alternative theories [ ]. For more details on this topic, see.

Because dark matter remains to be conclusively identified, many theories that aim to explain the observational evidence without invoking dark matter have emerged. The obvious way to do this is to modify general relativity.

General relativity is well-tested on solar-system scales, but its validity on galactic or cosmological scales is less certain. A suitable modification to general relativity can conceivably eliminate the need for dark matter. The most well-known theories of this class are and its relativistic generalization, and. Release Therapy Ludacris Rar. A problem with alternative theories is that the observational evidence for dark matter comes from so many independent angles (see the 'observational evidence' section above). Any alternative theory not only has to explain all the evidence, it also has to explain individual cases such as the, wherein observations indicate that the location of the center of mass is far away from the center of baryonic mass. Nonetheless, there has been some scattered successes for alternative theories, such as a 2016 test of gravitational lensing in entropic gravity.

The prevailing opinion among most astrophysicists is that while modifications to general relativity can conceivably explain part of the observational evidence, there is probably enough data to conclude there must still be some dark matter. In philosophy of science [ ] In, dark matter is an example of an 'auxiliary hypothesis', an postulate that is added to a theory in response to observations that it. It has been argued that the dark matter hypothesis is a hypothesis, that is, a hypothesis that adds no empirical content and hence is unfalsifiable in the sense defined.

In popular culture [ ].