Although
Dark Matter seems to be a fictional form, scientists have generally
acknowledged its existence. By going through various stages of mathematical
complexity, scientists have come to realize that 85 percent of the matter
scattered in the universe is this Dark Matter material, which does not absorb, emit
or reflect any kind of electromagnetic wave (light). Therefore, it is not
possible to directly identify this substance through a ground telescope or
space observatory or any spacecraft. It can only be determined by gravity.
Scientists believe that this substance has a strong presence in the expansion
and evolution of space.
When
it comes to human research on this subject, the first notable event is the
speech of the British scientist Lord Kelvin in the year 1884. There he spoke
about the Dark Body with the stars orbiting around the center of the galaxy.
According to him, after measuring and adding the mass of different stars in a
certain part of the galaxy separately, the total mass of that part was found to
be more than the previous sum. Immediately after this speech, the human began
to think of this subject. In 1906, the French mathematician Henry Poincare
first mentioned Dark Matter in his book 'The Milky Way and The Theory of
Gases'. In 1922, Dutch scientist Jacobus Kapteyn Speculated that the presence
of Dark Matter was the cause of repeated inconsistencies in measuring the
velocity of stars. The presence of this substance was estimated in 1932 by the
Dutch scientist Jan Oort, the famous Radio astronomer, and in 1933 by the Swiss
astronomer Fritz Zwicky. During his study of galaxies, scientist Zwicky
observed inconsistencies between the total mass of matter and the amount of
light emitted from it, and said that the mass of that part of the galaxy could
be at least 400 times greater than the mass measured in that particular region.
He named the substance Dunkle Materia. In 1939, American scientist Horace
Babcock encountered a similar experience while observing the Andromeda galaxy.
Scientists have believed the existence of Dark Matter since 1956, but
experiments by American scientists Vera Rubin, Kent Ford and Australian
scientist Ken Freeman in the 1970s and 1980s have revealed that there is much
more mass in the galaxy than the observable known mass, probably for Dark
Matter. Then, in the early eighties, the worldwide presence of Dark Matter was
unanimously acknowledged.
Scientists
say that this substance is made up of a particle whose properties are not yet
known. The most difficult task is to identify these particles in different
ways. However, subject to the presence of these particles, some evidence has
come before scientists through some experiments such as rotation of the galaxy,
gravitational lencing, cosmic microwave background analysis, temperature
distribution of hot gas, etc.
The
spiral arms of the spiral galaxy begin to rotate around the centre of that
galaxy. Just as in any stellar system the maximum mass is concentrated at the centre
of the system, same scenario should be observed at the centre of the galaxy, as
the distance from the centre of the galaxy increases, the density of the matter
should be decreased. In keeping with this, the velocity of rotation of matter
should be reduced as far as the circumference of the centre of the galaxy. But
in reality it is not. The rotational velocity of matter has been observed to be
almost the same everywhere, meaning that it is simply due to the activation of
invisible Dark Matter. In addition, a number of inconsistencies have been found
in the distribution of mass and kinetic energy in these cosmic structures using
the Viral Theorem, which is due to the strong presence of Dark Matter.
When
light travels from a very distant light source, it does not come directly to
the observer. Due to the presence of different substances between the light source
and the observer, some scattering in the path of light is observed. This
phenomenon is called Gravitational Lensing in the language of astronomy. In the
farthest reaches of space there is a cluster of galaxies called
MACS-J4-16.1-2403. Scattering was observed when light from that region came to
Earth. Experiments have shown that the amount of light scattering is much
greater than the observable mass between the galaxy cluster and the Earth,
which means that in this case also the activity of the Dark Matter is affected.
One thing should be understood here. We often hear the word Space-Time. In
fact, it is a theoretical model. Scientists have created a four-dimensional
Space-Time model by combining one-dimensional time with three-dimensional space
to accurately interpret various cosmic phenomena. In the case of Gravitational
Lensing, there is no direct correlation or interaction of light with the
activity of matter, nor is it possible. Here Space-Time is bent by the Dark
Matter and the light comes forward in according to that curvature and captures
us as a gravitational lens.
Based
on this information, scientists have been able to calculate the amount, pattern
of arrangement, and mapping of Dark Matter around the Milky Way galaxy.
Scientists have since used a variety of methods to determine the mass of many
more galaxies in space. In each case, they have found the same outcome. From
their experiments, we learned that the ratio of matter to observable matter in
space is 5:1.
‘Structure
Formation’ refers to the time when cosmic objects (galaxies, stars, planets,
satellites, etc.) were formed after the Big Bang. For a short time, however,
the effects of radiation were so strong in the early time of the formation of
the universe that the direct effect of it fell heavily on observable matter.
After this event, the formation of galaxies, stars, etc due to condensation of all
these observable particles was a great problem, and even after that, if all
these cosmic objects were formed, there would be insufficient time for the formation
of this universe for 1,830 crore years. But since light has no interaction with
Dark Matter, this problem has been solved, and within this time our universe
has come to a complete end.
Scientists
have come to realize that the effect of Dark Matter is beyond the scope of
general observation. The last sign of the Big Bang is the Cosmic Microwave Background.
If all the stars in the sky could be resisted in any way by obscuring the light
of the stars,satellites, nebula, then a glimmer of soft light could be seen all
over the sky which is called Cosmic Microwave Background. This light does not
originate from any object, but from the redshift that occurs as a result of the
gradual movement of matter, created at early stage of the creation of the
universe, away from us. Dark Matter influences the Cosmic Microwave Background
by influencing the density and velocity of all these distant substances. In
addition, the gravitational force of the Dark Matter affects the Cosmic Microwave
Background.
The
aftermath of the Big Bang caused a kind of vibration in the material that is
still going on. This vibration is called Baryonic Acoustic Oscillation. The
existence of this vibration can be understood by observing the Cosmic Microwave
Background at present. This vibration caused a change in the density of matter
in the universe. However, according to the calculations of the scientists, the
intensity of this vibration is not as much as it should be. This is because of
the presence of Dark Matter.
Scientists
speculate that Dark Matter may be associated with observable substances. In
this regard, their argument is that the vast empty area of space which we call
Cosmic Void is expanding much faster than the average speed of space as a
whole. (Link is given for details about Cosmic Void: https://spacejagat.blogspot.com/2020/02/c-osmicvoid-literal-meaning-of-these.html)
Again, in the galaxy-rich region which we call Cosmic Filament, the expansion
of space is much less than the average speed of expansion of the whole space.
The
WMAP Spacecraft conducted extensive research on Dark Matter from 2002 to 2012
and the Planck Spacecraft from 2013 to 2015, and based on the data sent by
these two spacecrafts, a map of a specific part of space was published in May
2021 with sufficient information. From there, scientists have published an account
of the various elements that make up space. According to them, if the combined
value of all the elements in space is taken to be 1 and radiation is excluded
due to the complexity of the calculation, then the value of Dark Energy is 0.690,
the value of observable matter is 0.0482 and the remaining 0.2618 is the value
of Dark Matter. (Link for details about Dark Energy is given: https://spacejagat.blogspot.com/2021/10/dark-energy-master-of-universe.html )
Many
scientists have created and published many models about Dark Matter, the basics
of which are roughly the same. It is made up of any one substance which can
only be identified by gravity. The matter that makes up our observable
galaxies, stars, planets, satellites, comets, etc., is called Baryonic matter.
But Dark Matter is not formed by this baryonic substance. In other words, they
are composed of those substances which are not observed through any way. That
is why we have so much trouble understanding this substance properly. Some say
that these substances may be made up of particles like protons or neutrons for
which they interact with gravity. Nowadays we hear of some particles that
produce Dark Matter such as Axion, Geon, Neutrino, Photino, Gravitino, Weekly
Interacting Massive Particle or WIMP, Gravitationally Interacting Massive
Particle or GIMP, Super Symmetric Particle, etc. Of these, we have been able to
identify the largest neutrino in terms of quantity, but its mass occupies only
a small part of the whole thermodynamics.
Particles
of Dark Matter are generally divided into three main classes viz. Cold, Warm
and Hot. However, temperature has nothing to do with this classification. This
classification is based on the velocity of Dark Matter or, to put it a little
better, momentum. Neutrino is an example of Hot Dark Matter, Photino, Gravitino,
etc. are the example of Warm Dark Matter and Super Symmetric particle is an
example of Cold Dark Matter. Of these, the speed of Hot Dark Matter is the
highest but the real controller of the universe is Cold Dark Matter.
When
a particle comes together to form a cosmic object, the primary condition of
that particle is to give up its inherent energy. If energy is not released, the
excessive momentum in the particle prevents it to from a large cosmic object.
Another thing is that, due to this excessive momentum the particle cannot take
part in the interaction with other particles. Since Dark Matter does not give
off energy, they have no other transformation, no stable state. For this
reason, Dark Matter has no direct role in the formation of this universe.
Scientists
are using two methods to find the Dark Matter. Scientists are working on the
method of direct identification by building laboratories in very deep underground
of different countries. Inert gases such as Argon, Xenon and cryogenic
solutions are used here. (In physics, cryogenic solutions are solution of very
low temperature) There are several such laboratories in the United States,
Canada, Britain, Spain, and Italy. Further research is under way into the
formation of Dark Matter by the collision of highly dynamic protons through the
Large Hadron Collider in CERN, Switzerland. Attempts are being made to find the
particles caused by the decay of the Dark Matter in the indirect detection
method. Scientists speculate that the centre of the galaxy may contain large
amounts of Dark Matter from which Gamma-ray or other particles such as Antiprotons
or other types of particles may be produced, as the abundance of these rays and
particles is abundant here. Scientists also believe that very powerful cosmic
rays could be generated from this material. Various telescopes, such as the
Fermi Gamma-Ray Space Telescope, and the Alpha Magnetic Spectrometer of the
International Space Station, have been continuously explored in this regard.
Not
only is Dark Matter scattered in space, it is also with us on this earth. They
have no restriction in movement. At any given moment particles of Dark Matter,
like a group of WIMP particles or other, can penetrate any object, even the
body of animal, plant or the crust of earth and again come out. Maybe while
reading this article, innumerable particles of Dark Matter went through your
whole body and came out again with the speed of a storm, you did not understand
anything. In fact, apart from gravity, these mysterious particles do not use
any other medium to express their existence or interact with other matter, so
we cannot understand them. There have been and still are many experiments with
these particles.
If
Dark Matter did not exist in this universe, then the creation of this cosmic
world would have been a problem. Even though, if the creation of the universe
were possible, it would still take much longer than it did now, the universe
would expand more rapidly, as the distant cosmic object orbiting
around the centre of the galaxy slowed down, it might have almost stopped, it
would have been difficult to explain the collision of the two galaxies
theoretically, the General Theory of Relativity would have gone wrong, and so
on.
Since
Dark Matter has not yet been definitively identified, in that sense many
scientists at home and abroad have been conducting extensive research by
creating models with a variety of theories. We cannot yet say for sure which of
these theories is actually compatible with Dark Matter. Therefore, patient
observation and extensive research is the only sure way to solve this problem.
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