Riddle of the missing mass
Non-baryonic dark matter
| ||Automatic translation|| ||Category: matter and particles|
Updated October 22, 2012
The universe does not consist only of atoms, 96% of our Universe is missing. It is a theory that we have difficulty conceptualizing. In northern England at the bottom of a mine at 1600 meters below the surface of the Earth, scientists seek a new fundamental particle tirelessly since the 1970s. In those years, science thought that the universe is complete and that the model is satisfactory. But in 1974, two researchers at Princeton, New Jersey, USA, decided to measure the amount of matter contained in the entire universe. Jeremiah Ostriker and James Peebles looks at the stability of galaxies, and they face a problem. The galaxies are not stable and their computer model shows that galaxies, after a period of rotation, unmade. To be stable it is, in theory, more material, thus more gravity so that everything does not collapse. Since there is no additional material, the two scientists for the purpose of a simulation, invented one, Dark Matter. The idea is not new because in the 1930s, Fritz Zwicky, Swiss-American astrophysicist (1898-1974) noted an anomaly. He realizes the Mount Wilson Observatory, observing a group of galaxies in the Coma cluster, the galaxies rotate around each other at full speed but the mass is not sufficient to prevent dissociate.
In 1933 he was the first to suggest the presence of invisible matter between galaxies but it will not convince anyone of the importance of his discovery, which will be forgotten for almost forty years. An astronomer, Vera Rubin, in addition to his 4 children, is dedicated in the 1970s, the study of galaxies. She realizes a fundamental discovery.
We know that everything is related to gravity in the solar system further away from the sun's gravitational force weakens further.
It is the same for galaxies where stars that revolve around an intense gravitational field. Vera Rubin noted that the stars do not slow down gradually as the distance from the center, their speeds are constant, the center to the periphery.
The conclusion is that lack of mass in the observable universe to ensure its stability. Dark matter, hitherto ignored, became fashionable in the scientific world.
| || |
Image: The analysis of the WMAP image of the sky, indicates that the universe is older than 13.7 billion years (with an accuracy of 1%), it is composed of 73% dark energy, 23% Cold dark matter, and only 4% of atoms. The universe is currently expanding at a rate of 71 km/s / Mpc (with an accuracy of 5%). it went through episodes of rapid expansion called inflation and grow forever.
Credit: WMAP Science Team, NASA
The missing mass
| || || || |
What is dark matter?
In astrophysics, dark matter (or dark matter) refer to the material apparently undetectable. Various hypotheses have been explored and the composition of the hypothetical dark matter, which emits no radiation, molecular gas, dead stars, brown dwarfs in large numbers, black holes, etc..
Scientists are mapping the universe by measuring the amount of hydrogen on a large scale, they find that even where there are no stars on the border of galaxies, the gas turns into orbit as quickly as the nearby stars the center. Hydrogen undergoes the same mysterious force. The rotation curves imply the presence of a force of nature non baryonic A baryon is in particle physics, a class of particles, whose best-known representatives are the proton and the neutron. The term "baryon"is derived from the Greek barys meaning "heavy" and refers to the fact that baryons are generally heavier than other types of particles. . Scientists expect so for several decades, the bottom of a mine 1600 meters, the hypothetical particle, the neutralino, is revealed. How non-baryonic particles will materialize on the screens of the machines baryonic? It sounds weird but it is the budget to spend.
Mordechai Milgrom of the Weizmann Institute in Israel, argues that the presence of dark matter is unnecessary and that gravity is stronger in some places. In 1981 he make public his theory, gravity variable, a concept that contradicts Newton extravagant. Scientists have ignored the concept. It has already changed the theory of gravitation to atomic distances, it is possible that the day you change for large galactic distances.
The structure of the universe, however, shows that the atomic matter represents only 4% of the total material. But dark matter is not the missing 96% of the universe. The Big Bang theory shows that the universe expands more and faster, accelerating its expansion.
The amount of energy needed to cause this acceleration is tremendous, this energy is called dark energy. Today, cosmology tells us that the composition of the universe is composed of 73% dark energy, 23% non-baryonic matter and 4% of baryonic matter.
This is the hypothetical result of the standard model simulated by computer. It's an illusion to show what is happening based on computer simulations.
Generate galaxies with computers is an aberration, given the number of unknown parameters to adjust, it is as if these scientists wanted to play the "creator". However, one of the major problems of modern astrophysics is that we ignore the essential nature of the universe.
The luminous matter, the only one we see directly, seems to represent less than one tenth the mass of the universe.
This light is our only source of information. The fact is that the universe is held by entities that we do not know if they exist.
A day will come when it will review the basis of the constitution of the cosmos.
| || |
Image: This gravitational lens shows some strange blue objects drawn. These objects dotting the image are multiple views of a single ring galaxy.
The singular form of the blue background galaxy (center) has allowed astronomers to deduce that it is reproduced on this image to 4 hours, 10 hours, 11 hours and 12 hours from the center of the cluster. In a very massive cluster of galaxies, the gravitational pull is so strong that space-time is warped by dark energy.
Amount of dark matter
| || || || |
Clusters of galaxies are objects of choice to study the problem of dark matter, because we can study their mass distribution by several independent methods.
We can analyze the movements of their galaxies, the properties of hot gas they contain, the gravitational lensing phenomena which are observed, disruption of the cosmic background radiation that they generate, the modeling of their formation by gravitational collapse.
Cosmology tells us that the composition of the universe is composed of 73% dark energy and 27% fat (23% non-baryonic matter and 4% of baryonic matter). The study of galaxy clusters indicates that 90% of their mass is invisible and the study of galaxies indicates that the vast majority of their mass is invisible. The observation of clusters of galaxies can show that dark matter is distributed in a less concentrated, more extensive, than ordinary matter.
The numerical simulations on the properties of the early universe, can find the distribution of dark matter around galaxy clusters.
Indeed, these simulations indicate that on small scales, dark matter would tend to form clumps, with masses ranging from that individual on Earth to that of a galaxy.
Dark matter is a pancake encompassing clusters of galaxies, containing a multitude of small lumps. Ben Moore has developed computer farms dedicated to this type of problem.
Image: Results from simulations conducted by Ben Moore. The picture shows an overview of the distribution of dark matter in a slice of the universe of 10 000 light years behind.
The two zoom lenses represent this region by 100 light-years, respectively, then 1 light year.
This image has required six months of calculation by computer farms.
Dark matter remains secret
| || || || |
The Big Bang theory to calculate the number of baryons in the Universe (atoms of hydrogen and helium-4), formed during the primordial nucleosynthesis. Astrophysicists have calculated the rate of baryonic matter that would be about 4% of the critical density. Now, to explain the flat geometry of the universe, the total matter of the universe must represent 30% of the critical density (the remaining 70% being dark energy). It therefore lacks 26% of the critical density of matter as non-baryonic and therefore made up of other particles than atoms. Many other indices converge to indicate that the universe contains a large amount of material in a non-luminous. In addition, the Big Bang model is in remarkable agreement with the observations, provided that the universe contains about 30% dark matter and about 70% of dark energy. Nevertheless, more and more astronomers believe that dark matter exists.
Rather than trying to explain the anomalies by unobservable matter, it would be more appropriate to review the physical laws that constitute the standard model, and which are in any way challenged by other more fundamental problems. Some physicists are turning to the example of string theory. String theory adds new dimensions to the usual four (three dimensions of space and time) and place the dark matter in these new dimensions which are inaccessible to us. Nuclear and electromagnetic forces, strong and weak, would be confined to our four-dimensional and could not leave. However, gravity could be dispersed in other dimensions, and thus decrease in intensity compared to other forces.
We can see that it is difficult to give a finite and coherent vision of the dark matter, because the subject is still booming.
| || |
Image: More and more astronomers believe that dark matter exists.