.Dark matter is a form of thought to account for approximately 85% of the matter in the and about a quarter of its total energy density. Its presence is implied in a variety of observations, including effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. For this reason, most experts think that dark matter is abundant in the universe and that it has had a strong influence on its structure and evolution.

Scalar field dark matter, ultra-light axion-like particle, wave dark matter, fluid dark matter, and repulsive dark matter are just a few. Despite the plethora of names, the theories are all roughly the same. They postulate that dark matter is formed from an immense number of tiny particles with exceptionally low mass.

Dark matter is called dark because it does not appear to interact with observable, such as, and so it is undetectable by existing.Primary evidence for dark matter comes from calculations showing that many would fly apart, or that they would not have formed or would not move as they do, if they did not contain a large amount of unseen matter. Other lines of evidence include observations in and in the, along with astronomical observations of the 's current structure, the, mass location during, and the motion of galaxies within. In the standard model of cosmology, the total of the universe contains 5% and, 27% dark matter and 68% of an unknown form of energy known as. Thus, dark matter constitutes 85% of total, while dark energy plus dark matter constitute 95% of total mass–energy content.Because dark matter has not yet been observed directly, if it exists, it must barely interact with ordinary matter and radiation, except through gravity. Most dark matter is thought to be non-baryonic in nature; it may be composed of some as-yet undiscovered. The primary candidate for dark matter is some new kind of that has, in particular, (WIMPs). Many experiments to directly detect and study dark matter particles are being actively undertaken, but none have yet succeeded.

Dark matter is classified as 'cold', 'warm', or 'hot' according to its (more precisely, its ). Current models favor a scenario, in which by gradual accumulation of particles.Although the existence of dark matter is generally accepted by the scientific community, some astrophysicists, intrigued by certain observations which do not fit the dark matter theory, argue for various modifications of the standard laws of, such as,.

These models attempt to account for all observations without invoking supplemental non-baryonic matter. See also:In standard cosmology, matter is anything whose energy density scales with the inverse cube of the, i.e., ρ ∝ a −3. This is in contrast to radiation, which scales as the inverse fourth power of the scale factor ρ ∝ a −4, and a, which is independent of a. These scalings can be understood intuitively: For an ordinary particle in a cubical box, doubling the length of the sides of the box decreases the density (and hence energy density) by a factor of 8 (= 2 3). For radiation, the energy density decreases by a factor of 16 (= 2 4), because any act whose effect increases the scale factor must also cause a proportional. A cosmological constant, as an intrinsic property of space, has a constant energy density regardless of the volume under consideration.In principle, 'dark matter' means all components of the universe which are not visible but still obey ρ ∝ a −3. In practice, the term 'dark matter' is often used to mean only the non-baryonic component of dark matter, i.e., excluding '.'

Context will usually indicate which meaning is intended.Observational evidence. Of a typical spiral galaxy: predicted ( A) and observed ( B).

Dark matter can explain the 'flat' appearance of the velocity curve out to a large radius.The arms of rotate around the galactic center. The luminous mass density of a spiral galaxy decreases as one goes from the center 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, it is expected that the rotation velocities will decrease with distance from the center, similar to the Solar System. This is not observed. Instead, the galaxy rotation curve remains flat as distance from the center increases.If Kepler's laws are correct, then the obvious way to resolve this discrepancy is to conclude 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 (dark matter) in the outskirts of the galaxy.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 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 dark matter outweighs visible matter by approximately 5 to 1. Gravitational lensing. Dark matter map for a patch of sky based on gravitational lensing analysis of a Kilo-Degree survey.One of the consequences of is 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.

Dark matter does not bend light itself; mass (in this case the mass of the dark matter) bends. Light follows the curvature of spacetime, resulting in the lensing effect. Cosmic microwave background. Main article: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 2003–2012, and even more precisely by the in 2013–2015. 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 (MOND).

Structure formation. 3-D 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 currently seen.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.

Bullet Cluster. Main article:If dark matter does not exist, then the next most likely explanation must be general relativity – the prevailing theory of gravity – is incorrect and should be modified.

The Bullet Cluster, the result of a recent collision of two galaxy clusters, provides a challenge for modified gravity theories because its apparent center of mass is far displaced from the baryonic center of mass. Standard dark matter models can easily explain this observation, but modified gravity has a much harder time, especially since the observational evidence is model-independent. Type Ia supernova distance measurements.

Main articles: andType 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. Data indicates the universe is expanding at an accelerating rate, the cause of which is usually ascribed to. Since observations indicate the universe is almost flat, it is expected the total energy density of everything in the universe should 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 which nonetheless behaves like matter (see technical definition section above) – dark matter. Sky surveys and baryon acoustic oscillations. Main article:Baryon acoustic oscillations (BAO) are fluctuations in the density of the visible matter (normal matter) of the universe on large scales.

These are predicted to arise in the Lambda-CDM model due to acoustic oscillations in the photon-baryon fluid of the early universe, 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 130–160 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 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. Their angular positions are unaffected.

This effect is not detectable for any one structure since the true shape is not known, but can be measured by averaging over many structures. It 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?Some dark matter hypothesesLight bosonsneutrinosother particlesmacroscopic(MaCHOs)(Macros)(MOG)(MoND)(TeVeS)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 neutrons. However, for the reasons outlined below, most scientists think the dark matter is 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 non-primordial, faint old and, collectively known as (MACHOs), which can be hard to detect.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 at most only 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 non-baryonic dark matter are hypothetical particles such as, (WIMPs), (GIMPs), particles,. 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 too 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). Dark matter aggregation and dense dark matter objects If dark matter is composed of weakly-interacting particles, an obvious question is whether it can form objects equivalent to,.

Historically, the answer has been it cannot, because of two factors:It lacks an efficient means to lose energy Ordinary matter forms dense objects because it has numerous ways to lose energy. Losing energy would be essential for object formation, because a particle that gains energy during compaction or falling 'inward' under gravity, and cannot lose it any other way, will heat up and increase.

Dark matter appears to lack means to lose energy, simply because it is not capable of interacting strongly in other ways except through gravity. The suggests that such a particle would not stay bound to the gradually forming object – as the object began to form and compact, the dark matter particles within it would speed up and tend to escape. It lacks a range of interactions needed to form structures Ordinary matter interacts in many different ways. This allows the matter to form more complex structures. For example, stars form through gravity, but the particles within them interact and can emit energy in the form of and through when they become energetic enough. And can bind via the and then form with largely through.

But there is no evidence that dark matter is capable of such a wide variety of interactions, since it seems to only interact through gravity (and possibly through some means no stronger than the, although until dark matter is better understood, this is only hopeful speculation).In 2015–2017 the idea dense dark matter was composed of, made a comeback following results of measurements which detected the merger of intermediate mass black holes. Black holes with about 30 solar masses are not predicted to form by either stellar collapse (typically less than 15 solar masses) or by the merger of black holes in galactic centers (millions or billions of solar masses). It was proposed the intermediate mass black holes causing the detected merger formed in the hot dense early phase of the universe due to denser regions collapsing.

However this was later ruled out by a survey of about a thousand supernova which detected no gravitational lensing events, although about 8 would be expected if intermediate mass primordial black holes accounted for the majority of dark matter.The possibility atom-sized primordial black holes account for a significant fraction of dark matter was ruled out by measurements of positron and electron fluxes outside the Sun's heliosphere by the Voyager 1 spacecraft. Tiny black holes are theorized to emit. However the detected fluxes were too low and did not have the expected energy spectrum suggesting tiny primordial black holes are not widespread enough to account for dark matter. Nonetheless, research and theories proposing dense dark matter accounts for dark matter continue as of 2018, including approaches to dark matter cooling, and the question remains unsettled.

In 2019, the lack of microlensing effects in the observation of Andromeda suggests tiny black holes do not exist. However, there still exists a largely unconstrained mass range smaller than that can be limited by optical microlensing observations, where primordial black holes may account for all dark matter. 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 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 ): Dark matter particles are classified as cold, warm, or hot according to their FSL; much smaller (cold), similar to (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 with galaxies forming first and galaxy clusters at a latter stage, while hot dark matter would result in a top-down formation scenario with large matter aggregations forming early, later fragmenting into separate galaxies; 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. Eternity warriors 3 wiki. 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. Efstathiou, C.S. Frenk, and S.D.M.

White, The evolution of large-scale structure in a universe dominated by cold dark matterAnother approximate dividing line is 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 Kelvins. Standard physical cosmology gives the size as 2 c t (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 approximately 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 mega, today, around the size containing an average large galaxy.The 2.7 million 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 one 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: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 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 and ) 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. Peter: '. 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 which explain the small mass through the.Warm dark matter. Main article:comprises 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 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.Hot dark matter. Main article: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,. 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 /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 the first objects that can form are huge -size pancakes, which then fragment into galaxies. Show instead that galaxies formed first, followed by clusters and superclusters 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 (ADMX) searches for.

Another candidate is heavy particles which 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.

Further information: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 in the form of light or, as they pass through sensitive detection apparatus. 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 with 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 100 mK, 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 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, SuperCDMS and XENON100.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 travels (approximately 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 0:03:13, 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 various astrophysical sources can mimic the signal expected from dark matter, and so multiple signals are likely 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 in 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, but scientists concluded 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 and in clusters of galaxies.The experiment (launched in 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 which 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. Any discovery from collider searches must be corroborated by discoveries in the indirect or direct detection sectors to prove that the particle discovered is, in fact, dark matter.Alternative hypotheses. Further information:Because dark matter has not yet been conclusively identified, many other hypotheses have emerged aiming to explain the observational phenomena that dark matter was conceived to explain. The most common method is to modify general relativity. General relativity is well-tested on solar system scales, but its validity on galactic or cosmological scales has not been well proven.

A suitable modification to general relativity can conceivably eliminate the need for dark matter. The best-known theories of this class are and its relativistic generalization (TeVeS),. Abound.A problem with alternative hypotheses is observational evidence for dark matter comes from so many independent approaches (see the 'observational evidence' section above). Explaining any individual observation is possible but explaining all of them is very difficult. Nonetheless, there have been some scattered successes for alternative hypotheses, such as a 2016 test of gravitational lensing in entropic gravity.The prevailing opinion among most astrophysicists is while modifications to general relativity can conceivably explain part of the observational evidence, there is probably enough data to conclude there must be some form of dark matter. In philosophy of science In, dark matter is an example of an auxiliary hypothesis, an postulate added to a theory in response to observations which it.

It has been argued the dark matter hypothesis is a hypothesis, that is, a hypothesis which adds no empirical content and hence is unfalsifiable in the sense defined. In popular culture. Since dark energy does not count as matter, this is 26.8/(4.9 + 26.8) = 0.845.

A small portion of dark matter could be baryonic and /. See. is a term often used nowadays as a substitute for cosmological constant. It is basically the same except that dark energy might depend on scale factor in some unknown way rather than necessarily being constant. This is a consequence of the and the observation that spiral galaxies are spherically symmetric to a large extent (in 2D).

Astronomers define the term to refer to ordinary matter made of, and, including and from the collapse of ordinary matter. Strictly speaking, electrons are not; but since their number is equal to the protons while their mass is far smaller, electrons give a negligible contribution to the average density of baryonic matter. Baryonic matter excludes other known particles such as.

Hypothetical primordial black holes are also generally defined as non-baryonic, since they would have formed from radiation, not matter.References.

Credit: Braine et al.The ADMX collaboration, a group of researchers working at universities across the U.S. And Europe, has recently performed a new search for invisible axion dark matter using a cavity haloscope and a low-noise Josephson parametric amplifier.

Cavity haloscopes are sensitive instruments designed to detect and study halos around luminous bodies or other physical phenomena. Josephson parametric amplifiers, on the other hand, are technological tools that can be used to manipulate quantum states of microwave light fields. In their recent paper, the researchers searched for dark matter axions in the galactic halo with a mass ranging between 2.81–3.31 μeV.

The results of this search could help to rule out previous theoretical predictions, informing the future search for invisible axion dark matter.' Our recent search was motivated by two different mysteries in physics, both of which would be solved with the detection of axion dark matter,' Nick Du, researcher at the University of Washington and co-author of the recent paper, told Phys.org.

'The first of these is the dark matter mystery.' Past physics studies have found evidence that what we ordinarily think of as matter only makes up approximately 15% of the total mass of the universe. The remaining 85% is thought to be composed of particles that do not absorb, emit or reflect light, and thus cannot be detected using traditional techniques for studying matter.This non-luminous material, known as dark matter, remains one of the greatest mysteries in contemporary physics, as researchers are still unsure about whether it exists and what it is made of.

While there have now been countless searches for dark matter using a variety of instruments, this mysterious material has so far never been observed or detected. Researchers Chelsea Bartram (Left) and Nicole Crisosto (Right) while conducting the search for axiom dark matter. Credit: Braine et al.' One possible solution to what dark matter could be comes from another field of physics, namely nuclear physics, in the form of another mystery known as the Strong CP problem,' Du explained. 'A popular solution to the Strong CP problem predicts the existence of a new particle known as the axion, and the properties of the axion make it a compelling candidate for dark matter. In looking axion dark matter, the ADMX collaboration hopes to solve both the Strong CP problem and the mystery as to the nature of dark matter.

'The haloscope used by Du and his colleagues consists of a resonant cavity placed inside of a large magnetic field. According to theoretical predictions, dark matter axions in the galactic halo should couple to the magnetic field in the cavity and produce photons. Credit: Braine et al.' In a way, our search for axion dark matter is quite similar to how a radio operates,' Du said. 'As the frequency of a radio is tuned, one can pick up on different radio stations.

In that respect, our experiment is similar, except that we don't know the frequency of our radio station and the signal is much weaker.' The search for dark matter axions has been ongoing for several decades now, and Du and his colleagues have already carried out a number of such searches using their cavity haloscope. While they were so far unable to detect invisible axions, the results of their recent experiment rule out a range of axion masses that were previously predicted by benchmark theoretical models of axion dark matter.' This is actually the second time our experiment has achieved this sensitivity to axion dark matter, but this time, we have tripled the range we covered in,' Du said. 'By achieving and expanding on this sensitivity, we've shown that in the continued search for axion dark matter, ADMX represents one of the best hopes for finding it.' Credit: Braine et al.The observations gathered by Du and his colleagues could inform future searches for dark matter axions, while also paving the way for novel theoretical predictions. The researchers are now conducting a new search for axion dark matter at higher frequencies.

If this search is also unsuccessful, they plan to continue searching for invisible axions at even larger frequencies.' At higher frequencies, axion dark matter becomes more difficult to detect, because the conventional cavities we would use are no longer as sensitive to axions,' Du said.

'However, we already have some interesting prototypes in place to get around this, such as experiments that use a multi-cavity array to to.'