Dark Matter

Dark Matter

Single superpower.Scattered in every corner of the universe. Its shape is much larger than our visible universe. Who does not see that power? Again, he is not black. An object completely invisible. It can be touched with the hand, it cannot be pushed. The gaseous substances in our atmosphere are also not visible. But we can feel them. Jhiri jhiri wind gives a touch of peace to the body, from that we can understand that they exist. Again, we do not see the molecules of the object. That is why the atom is not completely invisible. On the other hand, particles like quark-neutrinos are not visible. But with the help of detectors they can be identified. The original particles can never be directly identified. Is to be done indirectly. The lost mass of the universe cannot be detected by any detector. They do not even interact with any object or energy. So this earth, the mountains, the rocks, the metals, our bodies — everything can be pierced by that secret substance, which scientists call Dark Matter and Dark Energy.

If it cannot be seen, whose existence cannot be felt even by touch, whose hadith cannot be found even indirectly, then how can we understand that there is that object and power?

Yes, this is the question of lakhs of rupees. And the solution is due to the gravitational ball. The gravitational effects of those hidden substances and secret energy still remain today. And so scientists have been convinced of their existence. That gravitational effect is not exactly Newtonian gravitational effect. In fact, Newtonian gravity was never successful in larger work. His race is only to do our daily work in the world. Understanding Dark Matter or Dark Energy requires Einstein's theory of gravitation. The theory that Einstein published in 1915. This theory says that the force of gravity does not mean the attraction of one object to another. Gravity is a game of spatial geometry. Heavy objects bend the spacetime around it. When another object comes in that curved space, it seems that the two objects are attracted to each other. Dark matter and dark energy cannot break this space-time curve. So where can you go without being caught?

However, however, it remains the same today. The existence of dark matter has been found only by measuring with gravity. But even today, scientists have not been able to measure the amount of this hidden substance and secret energy in any place. So he still doubts whether they exist at all. No one can say yet when this suspicion will end and when the eye-ear will be degraded.

Little did scientists know before 1920 that there are more galaxies in the universe than our Milky Way galaxy. But then a decade later, scientists discovered many more galaxies. Not only that, they discovered that these galaxies do not exist separately. Many galaxies combine to form a galaxy. This group of galaxies is called a galaxy cluster. The Vargo cluster in which we live has 40 galaxies.

1933 Swiss astronomer Fritz Zwicki and Dutch scientist Ian Wort were studying the comma cluster. The cluster is 320 million light years away from us. There are about one thousand galaxies in this galaxy cluster. Zwicky was trying to measure the velocity of galaxies in that cluster. But in doing so, he got unusual results. The strong gravitational pull of galaxies holds the galaxies together. We have a world of liberation. If you throw something up at a speed faster than this, it will never come back to earth. Similarly, the sun also has a release velocity. Since the linear velocity of the earth is less than that speed of liberation, the earth does not move far away from the sun by falling out of orbit. In the same way, our sun is constantly moving around the center of the Milky Way. If for some reason the speed of rotation of the Sun is greater than the speed of release of the Milky Way, then the Sun will not be able to hold the Milky Way. Similarly, galaxies have a velocity in the cluster. Fritz wanted to measure the speed of galaxies in comma clusters. In doing so, a huge inconsistency was caught. The galaxies are rotating faster than the galaxies will be stuck in the cluster. Zwicky calculated that galaxies would fall out of the cluster and fall into space at this speed, but they are neatly enclosed inside the cluster. So what's the matter?

Then the scientists did another study. Using gravitational lensing, Ian Wort tried to measure the mass of galaxies in the universe. The mass of the universe can be measured in two ways. One - by measuring the amount of all the objects in the universe and with the help of the gravitational ball. Using gravitational lensing. Round the dam there. Scientists had an account of the coarse particles in the universe. From that the total mass of the universe can be deduced. That mass and the measured mass of Ort-Zuiki should be one. But the total mass of the universe was found to be many times more than the calculation. Where did this extra mass supply come from? Many scientists have studied it. But the calculations did not match.

In the 1960's, the American astronomer Vera Rubin said that the mass of the universe would be equal if the mass of the universe were hidden. Rubin added that these secret objects are made up of particles that are unknown to us. Light also has no effect on it. So our eyes and powerful detectors can easily evade.

We now know that only 4 percent of the universe is made up of visible matter. 98 percent have remained invisible. 21% of the invisible mass is hidden matter and the remaining 75% is hidden energy. The Big Bang, the expansion of the universe, etc. can be explained by taking into account this huge dark matter and dark energy. Einstein's gravity can also be explained. That is, there is no opportunity to question its non-existence. Does it just fill the mind? Scientists want to know, what are those ghostly hidden objects actually made of?

The most accepted models of the cosmology of the universe were established by Steven Weinberg, Abdus Salam and Seldon Glasho. In that model all the known particles (fermions) and force particles (bosons) have been placed. But the search for hidden particles cannot give that model. Another model called 'Super Symmetry' was erected in the 1980s. The purpose is to explain things like black holes or dark matter — where Newton-Einstein's model is ineffective, and quantum mechanics doesn't work properly. From the formula of super symmetry, scientists have been talking about a kind of particle for dark matter. The name is his wimp. The full name is Weakly Interacting Massive Particles. I.e. weakly interacting heavy particles. Scientists claim that such a particle only interacts with a gravitational ball. It does not interact with electromagnetic, strong nuclear forces, or even weak balls. So there is no chance of it colliding with solid matter or photon

The universe is basically made up of 3 kinds of conditions

5% common-substance

25% Dark-Matter

80% Dark Energy

Dark-matter and dark-energy are two completely different things. The word Dark is very confusing. Although Dark-Matter and Dark-Energy have not yet been incorporated into any mathematical model. But we have a good idea of ​​what they might or may not be.

Astronomy is a thousand-year-old branch of science. However, modern cosmology was born from Newton's universal law of gravitation. Newton's law of gravitation explains the dynamics of the solar system and even the entire galaxy. If we imagine a universe through Newton's law of gravitation, we will see some significant features of the universe, such as:

In Newton's universe, "space" and "time" are two very different and independent things. The "space" thing is "static" or immutable. Therefore, neither the Big Bang nor the expansion of the universe is possible in Newton's universe. In this universe, "space" is infinite, endless, and space develops over time.

In Newton's universe, on the other hand, the "time" thing is absolute. That is, in the universe, everyone's time is one and everyone's clock is moving at the same speed. It is because of this perfection of time that it is possible for Newton's universe to travel faster than light. For example, if an astronaut returns to Earth after traveling from a distant galaxy, the astronaut's time and Earth's time must be the same. And any motion to keep these two times one is permissible. In fact, in Newton's universe, the effect of a gravitational ball is instantaneous, such as: if the sun were suddenly lost to a miracle, the earth would immediately notice it.

Another important feature of Newton's universe is that the "energy" and "mass" of this universe are two different things. The cause of the gravity ball is “mass”; But energy has no mass, so energy cannot apply gravitational force in any way. That is, the gravitational force can only apply to things that have mass. The electromagnetic radiation that we see as an expression of energy cannot be applied by the force of gravity, nor are they affected by the force of gravity. As a result, only "matter" can be measured in Newton's universe; And “radiation” is dark-matter for this universe.

Let's look at Einstein's universe. Einstein published his theory of special relativity in 1905. This special-relativity theory replaces Newton's concept of "absolute time." According to special relativity, the only absolute thing in the universe is the speed of light in space. At the same time, Einstein proposed the similarity of "time" and "space", so in Einstein's universe they are collectively called "spacetime".

In Einstein's universe, "time" is a local measure. In every part of this universe, "time" is as different as "space." Moving from one point of space-time to another means the simultaneous travel of "space" and "time." This is why when an astronaut returns to Earth at the end of a long journey, the astronaut's time and Earth's time will be different.

Immediately after special relativity, Einstein proposed the equation e = mc ^ 2. Which indicates the equivalence of energy and mass. As a result, there was no more radiation or dark matter in Einstein's universe. The transition between mass matter and massless radiation in Einstein's universe is possible through the equation e = mc ^ 2.

The problem is that "acceleration" and "gravity" were not the two most important factors in special relativity. As a result, special-relativity could not change Newton's universe. About ten years later, in 1915, Einstein dropped the special relativity and proposed the general-relativity theory. In general-relativity theory, Einstein drew gravity. Einstein proposed the "principle of equivalence", which says that "acceleration" and "gravity" are in fact the same thing. This general relativity is Einstein's real universe, the universe we are talking about today is Einstein's universe.

In Einstein's universe, "mass" or "energy" bends space-time, and the "acceleration" that an object traveling in curved space feels is gravity. That is, gravity is the curvilinear acceleration of space-time. If space-time is not curved, gravity will not be felt. This means that Einstein's "space" is not as fixed or unchanging as Newton's.

So along with general-relativity, Newton's concept of "fixed space" also departed.

Interestingly, general-relativity theory is an equation of only one line, which has only three parts. The equation is given below. The leftmost part is a 4 × 4 matrix, which indicates how much space-time is bent. If the spacetime is not curved, each element of the matrix will be zero. The far right is the sum of "mass" and "energy" that is responsible for bending space-time. And the middle part is a constant.

It has already been said that it is possible to bend space-time in Einstein's universe. And this curvature can be of three kinds.

Positive-curvature: This type of curvature of any round surface. The sum of the three angles of any triangle on a positive-curved surface will be more than 180. The larger the triangle, the greater the sum of the three angles will be greater than 180. A universe whose spacetime is positive-curved is called a closed universe.

Negative-curvature: A good example of this type of curvature is: horse saddle. The sum of the three angles of any triangle on a negative-curved surface will be less than 180 °. The larger the triangle, the smaller the sum of the three angles will be less than 180. The universe whose spacetime is negatively curved is called the open universe.

Plane: This type of surface has zero curvature. The sum of the three angles of a triangle in any plane will be 180.

. The universe whose spacetime is negatively curved is called the open universe.

Plane: This type of surface has zero curvature. The sum of the three angles of a triangle in any plane will be 180.

If the curvature of spacetime can be determined, it is possible to determine for sure from the equations of general-relativity the amount of all matter and energy in the universe. Or vice versa; That is, if all the matter and energy in the universe can be quantified, then the curvature of spacetime can be determined from general-relativity. From this realization, in 1922, the Russian physicist Alexander Friedman presented Einstein's equation a little differently. Friedman suggests that the curvature of spacetime can be expressed in two ways:

Geometric: The curvature of spacetime can be geometric, which we have already discussed.

Expanding or contracting: We know that Einstein's universe is finite. So the curvature of spacetime can be expressed by the contraction or expansion of spacetime. That is, spacetime in Einstein's universe can be compressive, or expansive, or fixed in size.

In the early twenties, no one knew what these two types of curvature could be. Friedman's equation was as follows;

To the left of Friedman's equation ρ (Greek letter "row") indicates the energy density of the universe, we know "energy" and "mass" are the same thing, so they indicate the amount of matter and energy. H, on the other hand, is a measure of the elasticity of spacetime, called the habel-constant. And K is a geometric measure of the curvature of spacetime.

Historically, Einstein could not believe that spacetime could be compressive or expansive. So Einstein later added সাধারণ (lambda) to the general-relativity equation, in which space became space and then fixed. কে- is called cosmic-constant. In 1925, the American-Italian astronomer Edwin-Hable proved the expansion of the universe, leaving the Hubble-constant in Friedman's equation intact.

Below is Edwin Hubble's equation. The current value of H in our universe is 72 kilometers / second / megaparasec, and this value was determined by the American-Canadian astronaut Wendy Freedman.

Parasex is the unit of distance. 1 parasec = three light years (approximately), so 1 megaparasec = thirty million light years. H = 72 km / sec / megaparasek, which means: galaxies 1 megaparasek away are moving away from us at a speed of 72 km / sec; Similarly, galaxies 2 megaparasecs away at a speed of 144 km / sec, etc. And the reason for this speed is the expansion of space-time.

On the other hand, CMB (Cosmic Microwave Background) is used to determine the geometric curvature of spacetime. CMB is the fossil radiation of the Big Bang. The universe was impenetrable to light for about 400,000 years before the Big Bang. After these 4 million years, different charged particles begin to form atoms, as the universe gradually becomes clearer, and the radiation of the Big Bang begins to spread evenly throughout the universe. When this radiation is incident on a substance, the electrons of the substance scatter the photons of radiation, so that the radiation loses some energy, this radiation appears red in CMB. So the red spots of CMB indicate the presence of matter in the universe and the blue spots indicate the non-matter region of the universe.

If the brightest red spots on the CMB are more than 1 ড়া horizontally, the spacetime will be positive-curved and the universe will be closed. If less than 1 ১, space-time will be negative-curved and the universe will be open. And, if 1 is equal to °, the spacetime will be flat. In 2013, CMB data from WMAP satellites were analyzed and only 0.4% marginal error results were released. According to these results our universe is flat.

Now, if Windy-Friedman's "H" and "K" from WMAP were placed in Friedman's equation, we would be able to quantify everything in the universe. The problem is, the amount of space we get from real observation is 60% less than Friedman's! As mentioned earlier, neither radiation nor matter can evade Einstein's gravity. So, the idea is that this 80% hidden thing is a special kind of energy that does not fall within the standard-model of physics. We call this hidden energy of the universe Dark-Energy.

On the other hand, there is a huge gap in the 30% of calculated things. Ghaplata started in 1930, but we will start from the seventies. We know that Mercury and Pluto are the fastest orbital centers of the Sun in the solar system. The reason is the gravitational force of the sun; The Sun's gravitational force applied to Pluto is much less than that of Mercury, so Pluto's rotational speed is also less than that of Mercury. This relationship of rotation with gravity can be shown through a diagram, called a rotational curve. The rotational-curve in the solar system accurately explains the gravity of the sun and the rotational speed of different planets.

In the seventies, American astronomer Vera Rubin analyzed the rotational curves of many galaxies. He chose in his analysis the stars at the very ends of galaxies. Our present knowledge suggests that the gravitational force at the far end of the galaxy is small so the rotational speed of these distant stars will be relatively low. But, Rubin's rotational-curve is another thing. According to Rubin's analysis, the rotation speeds of the galaxy's peripheral stars are equal to those of the galaxy's inner stars. It has been calculated that the amount of matter needed to create the gravitational force required for this rotational speed of stars is five times less than the amount of matter in the galaxy. General objects here include: gas, stars, black holes and other objects whose existence can be determined by electromagnetic waves. That is, we do not know the whereabouts of the 25% of the 30% calculations that we have been able to match in Friedman's equation. This 25% is what we call dark matter. Dark-matter cannot hide from gravity, but they are invisible in any electromagnetic spectrum.

There is a lot of diversity in galaxies. Some galaxies are of the spiral type, some are elliptical. Some galaxies are huge, some are dwarf in nature. Because of these differences, galaxies cannot be ideal models of the universe. The question may arise that while there is no such thing as dark-matter, Rubin's rotational-curve may indicate a feature of galaxies that we do not yet fully understand. So we should observe a structure that accurately represents the universe. One such structure is the galaxy-cluster.

The shape of a galaxy is much like a plate, so its rotational-curve is easy to determine. But, the size of the galaxy-cluster is like a cube. Therefore, the rotational speed of different galaxies in a cluster is determined in the Newtonian method to determine the rotational-curve of a galaxy-cluster. In the 1930s, the American physicist Fritz Zwicky observed in a rotational-curve analysis of coma-clusters that the rotational speed of the marginal galaxies of the cluster was equal to that of the inner galaxies of the cluster. That is, the results of Rubin and Zwicky are exactly the same.

About two-thirds of the ordinary matter in a galaxy is free hydrogen gas. When multiple galaxies form a cluster, these gases are heated under intense gravitational pressure and emit X-rays. Let's show the matter through bullet-cluster:

, There are two spherical structures of bullet-clusters in visible wavelengths, consisting mainly of galaxies. However, at the X-ray wavelength, all the hydrogen gas in the cluster can be found outside the two spheres, in the center of the cluster. This hydrogen gas is two thirds of the total mass of the common material in the whole cluster.

, When forming clusters, galaxies pass through each other in the past. Since galaxies have a lot of space in between, the galaxies pass through each other unhindered and form two spherical structures. But, at the same time, the gaseous parts of the galaxies collide with each other, and lose momentum and begin to accumulate in the center of the cluster.

The same is true of single galaxies. Although a galaxy looks like a plate, bringing dark matter into shape would make the galaxy look like a huge hollow sphere.

Used to determine the general mass of the universe: optical, X-ray, infrared, or gamma telescope. Dark-matter, on the other hand, does not respond to electromagnetism. But, like ordinary matter, dark matter responds to gravity. So gravitational-lensing is used to determine the existence of dark-matter. The special gravitational-lensing method used is called microlensing. When a galaxy-cluster is observed, light from other distant galaxies behind the cluster bends due to the gravity of the cluster

In the microlensing method, the gravitational force is measured in a cluster with many such small lensing effects. The amount of all common-matter and dark-matter responsible for this gravity is then determined. Excluding ordinary matter from the electromagnetic spectrum, the amount of dark matter is obtained. NASA recently used their COSMOS or Cosmic Evolution Survey to create three-dimensional images of dark-matter by observing a tiny fraction of space with all their optical, X-ray, infrared, and gamma telescopes. That part of space was only eight times larger than the moon.

The Dark Matter and Dark Energy that have been talked about for so long have their origins in Einstein's general relativity. So, these are not the crops of our ignorance. And at this stage it is certain that neither dark matter nor dark energy is one of the most successful branches of physics in the standard model.