Theory How Is Matter Distributed in Universe?

It took between the first few minutes and the first billion years only, to that much of the Universe's normal matter made its way into cosmic dust, gas and objects such as stars and planets that still exist today. Visible stars and nebulae account for only 0.6 per cent of the Universe. What is called baryonic dark matter (all what is made of atoms -protons and neutrons are the most common baryons) account for 3.4 per cent of the Univers. Stars, the interstellar environment and hot gasses of galactic clusters contain only 50 percent of the baryonic matter as the missing remaining part exist in the form of filaments of diffuse gasses, which link the galaxies (usually, the total mass of normal matter which was present about 400,000 years after the Big Bang should still be observable today as it is not. Such that missing matter might be in hot gas located either in the space between galaxies or in galactic halos). The non-baryonic dark matter -the famous dark matter, strictly speaking- which is some unknown matter, exotic particles still to be discovered, accounts for 26 per cent. Dark matter doesn't yield light nor act upon it as it interacts normally with gravity but only weakly with any other existing force in the Universe. Dark matter thus is only detectable through the gravitational pull it yields. Scientists were brought to assume this non-baryonic dark matter on the basis that the gravitational behaviour of the Universe may not be explained throuhg the matter (visible ou not) which may be observed. Vera Rubin, an astronomer at the Carnegie Institution of Washington had studied the speeds of stars at various locations in galaxies and observed that there was virtually no difference in the velocities of stars at the center of a galaxy compared to those farther out, which is against basic Newtonian physics implying that objects on the outskirts of a center of gravity should orbit more slowly. A invisible mass that was to became the 'dark matter' was hypothethized to account for the phenomenon. Ninety-nine percent of the ordinary matter in the Universe generally is thought to be in the form of plasma, or clouds of ions and electrons as 'dust in a plasma' conditions are also common in interplanetary space. Dusty plasma are also thought to exist in comet tails and dust rings around the Sun. Our current understanding is that all galaxies exist inside clumps of dark matter. Without the constraining effect of dark matter’s gravity, galaxies would fling themselves apart as they rotate

The baryonic dark matter (one had first thought about feeble dwark stars, wandering planets or "quark nuggets" -objects weighing 4 tons for 1/25th of an inch) may be understood as (total, as said, 3.4 per cent):

• 0.4 per cent of gas and dust (from the dark nebulae in the galaxies to the super-hot gaz of the galaxies clusters). A recent study -November 2002, Jelle Keestra, with the ESA XMM/Newton- shows that the share of the super-hot gaz of the galaxies clusters would be much more important than thought: 50 per cent of the mass necessary to the clusters to keep the said gaz from evading the cluster
• cold and dark hydrogen clouds between galaxies: 1.2 per cent
• the remaining one third is missing from 'normal' matter. It is likely made of gigantic strands or filaments of warm (temperature less than 100,000 Kelvin) and hot (temperature greater than 100,000 Kelvin) gas in intergalactic space. These filaments are known by astronomers as the 'warm-hot intergalactic medium' or WHIM. WHIM's existence has been hypothetized due to that baryonic matter steadily decreased through cosmic history. The WHIM radiates a x-ray glow. Recent studies have showed a contrario this gaz (it silhouettes the NGC 891 galaxy, it blocks some of the x-rays emitted by quasars). The WHIM accounts for 1.8 per cent of the Universe. Recent studies show that the certainty is arising that, in all the Universe, great rivers of hot gas are bridging galaxies. It seems that this hot gas be the remainders of the early Universe (it would be in fact the material which would not have fallen into forming galaxies as first great structures of the Universe appeared about 13 billion years ago; 20 per cent of the "normal matter" then formed the galaxies and the remaining 80 per cent (normal matter), with dark matter, then formed the filamentary structure joining galaxies, clusters of galaxies). This hot gas seems to have appeared through normal matter components (baryons) colliding at some point after the Big Bang; these baryons colliding heated extremely the gas and the particules became invisible (they are presently visible only in ultraviolet). This gas would so figure up to 80 per cent of the normal matter, and, above all, it would help to locate the associated regions of dark matter). This hydrogen, before it could turn into the first objects of the Universe, first transformed itself into the 'molecular hydrogen', where two atoms of hydrogen link to form a molecule. Another view of the WHIM is the following. Astronomers, on the other hand, are calling 'missing matter' a part of the Universe's matter with is composed of baryons and missing for a half of its amount. It is mostly found in a web of hot, diffuse gas known as the Warm-Hot Intergalactic Medium (WHIM). Scientists think the WHIM is material left over after the formation of galaxies, which was later enriched by elements blown out of galaxies. The Sculptor Wall, at 400 million light-years from the Earth, is a large diffuse structure stretching across tens of millions of light years, containing thousands of galaxies and potentially a significant reservoir of the WHIM. The WHIM, generally, has a density equivalent to only 6 protons per cubic meter as the interstellar medium typically has about a million hydrogen atoms per cubic meter. Most of the WHIM is thought to have a temperature of about a million degrees where most of the WHIM is predicted to be found. As light from luminous quasars voyages to Earth, it illuminates clouds of intergalactic hydrogen gas that absorb light at specific wavelengths depending on the distances between each quasar and these clouds. This leads to an irregular pattern of quasar light known as the 'Lyman-alpha forest.'

->Hydrogen, Helium, and Others
Most of the ingredients in the Univers today are hydrogen and helium. These cosmic lightweighted eleemnts fill the first two spots on the famous periodic table of the elements. Less abundant but more familiar to us are the heavier elements, meaning everything listed on the periodic table after hydrogen and helium. These building blocks are elements such as iron and other metals. The metallic atoms seem well be part part of the hot gas, or "intergalactic medium," that lies between galaxies in the galaxy clusters, like a 2009 study has shown, as such heavy elements until know had been observed only from stars in the Milky Way or in other galaxies, generally. In a 7 millions years wide cluster, a team of scientists found that chromium 30 millions the Sun's mass, or manganese 8 million solar masses were lying. It's likely that the superwinds of the supernova creating those heavy elements are outflowing those into the intergalactic void. In the case of the cluster above mentioned, the study thinks it took some 3 billion supernovas to produce the measured amounts of elements and that they were brought out to the void of the cluster over periods up to billions of years. Elements essential to life are also parts of such heavy compounds produced by supernova

->The web, filamentary Universe is composed mainly of the 'intergalactic medium' (IGM), which is mostly ionized hydrogen with a density slightly higher than the average one of the Universe. As a whole process by which the filaments form (gravitational collapse, shock waves coming from the galaxies, ionization by the AGNs), and a reservoir of hydrogen into the voids of the filaments, are heating the material, the IGM then turns into the 'warm-hot intergalactic medium' (WHIM). One recently found that those filaments further are laced with highly ionized oxygen, which was expelled by the first explosions of stars. The voids between the filaments, as populated too by hydrogen is thus providing for more the birth of dwarf galaxies and stars along the next billions of years. The whole mechanism of the filamentary Universe, at last, is bound too by the action of the elusive dark matter. At the intersections of the filaments are to be found the galaxy clusters -also termed 'collapsed halos'

The Abell 1689 galaxy cluster helping to better quantify dark energy. courtesy NASA/ESA/JPL-Caltech/Yale/CNRS

Dark matter particles have very high energies, and even the most advanced accelerators cannot produce them. Scientists mostly first turned, since the 1980's to the WIMP hypothesis, the one of weakly interacting massive particles, or WIMPs, like the constituents of dark matter. Data from a study in 2018 suggest that WIMPs -- should they exist -- interact even more weakly with ordinary matter than previously thought. Scientists also moved, for example to the theory of exotic axion particles, which are akin to strange, massive photons, or also looking at whether dark matter might not interact with known particles at all, but exist in a 'hidden sector.' Dark matter neither emits nor absorbs light as it primarily interacts with the rest of the Universe through gravity. Astronomers see its effects only in the rotation of galaxies, in the distortion of light passing through galaxy clusters, and in simulations of the early Universe, which require the presence of dark matter to form galaxies. The leading candidates for dark matter are different classes of hypothetical particles. Scientists think gamma rays, the highest-energy form of light, can help reveal the presence of some of types of proposed dark matter particles. After studies of the center of our Milky Way Galaxy and small satellite dwarf galaxies candidate-particles within a specific range of masses and interaction rates were eliminated. As far as the axion-like particle model (gamma rays would convert into hypothetical axion-like particles and back) is concerned, a small range of such particles that could have comprised about 4 percent of dark matter are excluded. In some versions for the dark matter, colliding WIMPs either mutually annihilate or produce an intermediate, quickly decaying particle. Blazars and other discrete sources have been also seen accounting for nearly all of the emission of EGB ('extragalactic gamma-ray background') gamma rays, which might be due to interactions of dark matter particles, such as the annihilation or decay of WIMPs. The EGB was first measured by NASA's Small Astronomy Satellite 2 in the early 1970s. Dark matter as particle would have appeared nearly immediately after the Big Bang, long before the ordinary matter form. In the irregularities amplified by inflation, dark matter played the role of gravitational anchor point, allowing irregularities to grow, to attract matter and to become places of formation of stars and galaxies (from this, one think, too, that dark matter is linked to galaxies, and that these halos of dark matter are up to 10 times more important than the galaxies themselves). The non-baryonic dark matter should, too, like the WHIM, be distributed in net and filaments. Dark matter, from a simplier point of view, neither produces nor obscures light as its gravity corrals normal matter. It might be made of a type of as-yet-unknown subatomic particle, which, if the case, might interact with each other. Dark matter's effect on gravity is significant as it makes galaxies spin faster than expected, for example, and that it can affect the light of visible matter in still not understood ways. The four possible types of matter known are, by 2010, cold dark matter, warm dark matter, hot dark matter and baryonic matter. The Big Bang model should feature dark matter, if any, under the cold variety as warm dark matter should be ruled out by early reionization, and is estimated to make up about 23% of the matter-energy. In an 'extended model' hot dark matter would be the neutrinos. Dark matter does not slow down when colliding with itself, like observed during collisions between galaxy clusters narrowing the set of possible candidates in 2015

->Dark Matter Possible Candidate Particles
The WIMPs, Weakly Interacting Massive Particles, are diverse subatomic particles which may have been formed in the very early Universe at very high temperatures (Boulby Underground Laboratory for Dark Matter Research, UK, is aimed at studying them). WIMPs have their own antimatter counterparts and when both colliding that should yield a pair of daughter particles — an electron and its anti-particle, the positron. Some state that a WIMP would be its own antiparticle and, when two of them get together, they annihilate, producing known particles like electron/positron pairs, proton/anti-proton pairs, and gamma rays. If astronomers can detect a abundance of positrons peaking at a certain energy, that could indicate a detection of dark matter, because while electrons are abundant in the Universe, there are fewer known processes that could give rise to positrons. Positrons produced by dark matter annihilation would have a very specific energy, depending on the mass of the WIMPs making up dark matter. Another telling sign is the question of whether positrons appear to be coming from one direction in space, or from all around. If they're from dark matter, scientists expect them to be spread evenly through space, instead from a single direction. Other particles are too ranking like dark matter. Photinos, gravitinos, axions and magnetic monopoles. As a candidate, there is, too, the famous neutrino, long searched by physicists, and, indeed, the only particle which may be dark matter and which has really been detected (however, neutrinos should contribute only for a small part to the whole of dark matter). All these candidates sort as dark matter comes in two flavours, cold and hot function of the mass of particles which are constitute it. Cold dark matter (cold for particles moving slowly or having little pressure) would account for small structures level (galaxy formation, dwarf galaxies included) as hot dark matter (hot for particles moving quickly) would for large scale gravitational effects and clusters of galaxies. The first form would be made of WIMPs, axions, MACHOs, etc as the latter would be related to a non-zero neutrino mass. A recentest candidate for dark matter is a particle known as the neutralino as if extant, neutralinos exist, they should give off a large number of high-energy anti-electrons when colliding with each other. Many scientists think that the mystery of dark matter likely will be solved with the discovery of new kinds of subatomic particles, types necessarily different from those composing atoms of the ordinary matter. The search to detect and identify these particles is underway in experiments both around the globe and above it. A accurate study in 2012 of 10 dwarf galaxies that orbit our own Milky Way has produced some of the strongest limits yet on the nature of such hypothetical particles as such spheroidal dwarfs are known to possess large amounts of dark matter. Gamma rays with energies in the range from 200 million to 100 billion electron volts (GeV) were analyzed as a statistical technique found no gamma-ray signal consistent with the annihilations expected from four different types of WIMP particles was found. Such results show that WIMP candidates within that specific range of masses and interaction rates cannot be dark matter (WIMPs, or 'Weakly Interacting Massive Particles,' may mutually annihilate when pairs of them interact, a process expected to produce gamma rays)
A recent search to find how dark matter was to be extant in the vicinity of our Sun have shown that no dark matter is there, rendering that elusive concept even more mysterious! Accepted theories indeed stated that the neighborhood of the Sun should be filled with dark matter, with billions of these particles rushing through us every second. Dark matter is colder than we knew at smaller scales and forms small clumps, not only galactic scaffolding. Such small clumps even don't hold any galaxy
The Sanford Underground Research Facility in Lead, S.D. inside the now-shuttered Homestake Gold Mine nearly 5,000 feet beneath the surface is a new, mid-2012 laboratory which will search for the elusive dark matter as so far underground would help shield it from cosmic radiation. The detector in the laboratory further is submerged in water to insulate it. A rare form of radioactive decay could also be part of the facility, which has been funded by a mix of private donations and state and federal funding
Galaxies, which contain stars made of ordinary matter, likely form because of fluctuations in the density of dark matter. Gravity acts as the glue that holds both the ordinary and dark matter together in galaxies. According to calculations done in the 1990s and simulations performed in the decade before 2015, dark matter forms 'fine-grained streams' of particles that move at the same velocity and orbit galaxies such as ours. When such a dark matter stream goes through a planet, the stream particles focus into an ultra-dense filament, or 'hair,' of dark matter as Earth's gravity, for example, would focus and bend the stream of dark matter particles into a narrow, dense hair. When particles of a dark matter stream pass through Earth’s core, they focus at the root of a hair, where the density of the particles is about a billion times more than average. The root of such a hair should be around 600,000 miles (1 million kilometers) away from the surface. The stream particles that graze Earth's surface will form the tip of the hair, about twice as far from Earth as the hair’s root

->Astronomers on The Way to A Better Understanding of Dark Energy?
Astronomers are advancing on the way to a better understanding of dark energy as they are now using the advantage of gravitational lenses, like massive galaxy clusters. As the light of more distant galaxies is passing through such objects and their image fragmented into multiple distorted images, the observers are able to figure out how the light of those is being bent by the cluster, a characteristic that depends on the nature of dark energy! Such a method necessitates precise ground-based measurements of the distance and speed at which the background galaxies are traveling away from us along with specialized mathematical models and precise maps of the matter 'both dark and "normal' constituting the foreground cluster. Such studies could lead to quantify the strength of the dark energy that is causing the Universe to accelerate and a explanation of that force. As of August 2010, a study using the Abell 1689 cluster located 2.2 billion light-years away, significantly increased the accuracy of dark energy measurements. The latest results by 2016 confirm earlier studies that the properties of dark energy have not changed over billions of years. They also support the idea that dark energy is best explained by Einstein's 'cosmological constant' as it is equivalent to the energy of empty space

A other major step might have occurred by early 2012 in the comprehension of dark matter as a 1 billion light-year wide map of it was created. Scientists used the light travels from distant galaxies which were bent around distortions in space-time by dark matter gravitational pull, revealing an intricate web of dark matter and galaxies. A larger map still should come after that
The presence and distribution of dark matter in galaxy clusters can also be understood in terms of the dynamics which forms such gatherings. Giant galaxy clusters usually result from the merger of several, smaller ones. During such collisions, basic theories of dark matter, predict that galaxies remain anchored to dark matter as clouds of hot, X-ray emitting intergalactic gas, however, plow into one another, slow down, and lag behind the impact, a evidence to the collision. During a collision between two galaxy clusters, on a other hand, the hot gas is slowing down, while the dark matter is not. The Bullet Cluster has become a example of how dark matter should behave. The Abell 520 cluster however has had dark matter to collect into a 'dark core,' a clump of dark matter left behind from the wreck, and also rich in gas, containing far fewer galaxies than would be expected if the dark matter and galaxies remained anchored together. Most of the galaxies apparently have sailed far away from the collision. Six examples of high-speed galaxy cluster collisions have been mapped in terms of dark matter as the Bullet Cluster and Abell 520 are resulting from recent mergers. They are inconsistent with each other and no single theory explains the different behavior of dark matter in those two collisions. In one scenario, astronomers think that some dark matter may be 'sticky.' Like two snowballs smashing together, normal matter slams together during a collision and slows down. As dark matter blobs usually pass through each other during an encounter without slowing down, some dark matter would interact however with itself and stays behind during an encounter. Another scenario proposes that the specificity of the Abell 520 cluster results merely from a more complicated interaction than the Bullet Cluster encounter, with a collision between three galaxy clusters, instead of just two. A third possibility is that the core contained many galaxies, but they were too dim to be seen as they would have to have formed dramatically fewer stars than other normal galaxies. Such studies generally are also comforting the idea according to which dark matter does not interact with itself. Analysis by late 2016 at the European South Observatory (ESO) suggests that dark matter may be less dense, less clumpy and more smoothly distributed throughout space, which is in disagreement with earlier results from the Planck satellite

->More About Galaxy Clusters and Dark Matter
Galaxy clusters, which consist of thousands of galaxies, are important for exploring dark matter because they reside in a region where such matter is much denser than average. Scientists believe that the heavier a cluster is, the more dark matter it features around. A advanced view is that it might the internal structure of a galaxy cluster is linked to its dark matter environment. The closely packed a cluster is with galaxies, the lesser the density of its environment in terms of its neighbouring clusters, which also means that the surrounding dark-matter environment determines how packed a cluster is with galaxies. The connection between a galaxy cluster and surrounding dark matter is not characterized solely by cluster mass, but also its formation history. Younger clusters live in different large-scale dark-matter environments than older clusters. That connection between the internal structure of galaxy clusters and the distribution of surrounding dark matter is a consequence of the nature of the initial density fluctuations established since the Big Bang occurred (and they were amplified throught the inflation episode)

At last, the remaining of the Universe, 70 per cent, is the dark energy, responsible for the acceleration of the expansion of the Universe. Dark matter should not only be thought under the form of halos surrounding galaxies and galaxies clusters but under the form of clumps, themselves alike galaxies or globular clusters too. Dark matter has a dynamic life of its own. And ordinary matter is gathering around some of these clumps and not around each. E.g. our Milky Way has a dark matter halo but too thousands dark matter satellites clumps around it, which are constantly in movement. Dark matter motion may be modeled as a Brownian motion (i.e. like the random motion e.g. of dust in the air)