We are so busy with our day to day life that we never think about what is out there in the universe. We just know a few stars and some space things. But do ever we think of what is that black thing we see at night? What is behind the stars? We are so involved in what is in front of us that most of the times we only believe in things we can see. If I tell you to close your eyes and then tell you that there is a glass on a table. You would probably react saying, “how can I believe?”. But in reality, there is a glass on a table. The exact same thing is happening with us about dark matter. We can see things because of the light. And the things we can see because of light are called Matter. There is only 5% of the matter in the Universe. And 27% of the dark matter in the Universe. Other is Dark Energy which is 68%.
WHAT IS DARK MATTER
25% of the mass of the universe is made up of the material that No one can see is called dark matter. It is not made of baryon particles, which includes protons and neutrons. Because it does not absorb light or emit. We can not even say that it is anti-matter. Because it carries the opposite charge of the matter. When matter and anti-matter come together, they make energy. And dark matter does not do that. Now there is a question that if we cannot see it then how we can say that there is a dark matter. Whenever we need to study a mass of the object, first we study its motion.
In 1950, some astronomers were studying on spiral galaxy. While studying they saw something weird. It was said that those objects which are closer to the center of the galaxy will move faster. And those who are far from galaxy will move slower. But astronomers saw that the objects which are far from the center were moving faster. Even they were moving faster. They were not getting a break. And this will happen only when there is a presence of matter. So it proves that there is a matter which we can not see. so we call it dark matter.
AS PER EINSTEIN`S THEORY OF RELATIVITY
As per the theory of relativity, If an object contains mass. It will create a curve. And when light passes through a matter it will bend. So if there is dark matter, it will create a curve. And whenever the light will pass through it, It will bend. And according to this theory, scientists have made a map of dark matter. Where ever they can`t see the matter and light bends there is dark matter.
Even after this scientists were taking so many efforts. In 2011, scientists placed a particle detector at the international space station, to detect dark matter. Its name was Alpha Magnetic Spectrometer AMS. It has detected more than 100 rays. But still, it didn’t give so much information. And then the researcher decided that if they are unable to find dark matter. So they started finding things which were happening because of dark matter. Researchers believe that when an ordinary matter comes together it emits radiations. The same thing will happen about dark matter. And it will be known as dark radiation. And if we detect this we will find it.
Large underground xenon, LUX is working for the same purpose. This experiment is similar to AMS. Which aims to detect weakly interactive massive particles and dark matter interacts with ordinary matter on the earth. Dark matter in our galaxy was never directly detected in an experiment. LUX utilizes a 370 kg liquid xenon detection mass. This liquid is utilized in a time-projection chamber to identify individual particle interaction.
The detector is isolated from background particles. It is surrounded by a water tank and above the earth. So shielding reduces cosmic rays. And the radiations are interacting with the xenon. The interactions in liquid xenon generate 175 nm ultraviolet photons and electrons. The photons are immediately detected by two arrays of 61 photomultipliers tubes. Which are at the top and bottom of the detector. These prompt photons are the S1 signal. The electrons are generated by particle interactions. It drifts upwards towards the xenon gas by an electric field. The electrons are pulled in the gas at the surface by a stronger electric field. It produces electroluminescence. And the photos are detected As the S2 signal. The S1 and S2 signal constitutes a particle interaction in the liquid xenon.
The detector is a time-projection chamber. It uses the time between S1 and S2 signals. So it finds interaction depth of the dark matter.
These structures are larger than galaxy-sized as well as Big bang cosmology. In the observable universe, dark matter accounts for the vast majority of mass in the observable universe.
Fritz Zwicky used it for the first time. He used it to declare observed phenomena. Which was consistent with dark matter observations. As the rotational speeds of galaxies. It also observed orbital velocities of galaxies in the clusters. Gravitational lensing of background objects by galaxy clusters. And it also does temperature distribution of hot gas in galaxies and cluster of galaxies.
Dark matter also plays a central role in structure formation and galaxy evolution. It has measurable effects on the anisotropy of the cosmic microwave background. So now all the lines of evidence suggest. Galaxies, clusters of galaxies, and the universe as a whole contain far more matter. The matter which interacts with electromagnetic radiation is less. And this remainder is known as “ Dark Matter Component”.
The composition of dark matter is unknown. But it may include ordinary and heavy neutrinos. And recently they postulated elementary particles such as WIMPs and axions. Also astronomical bodies such as dwarf stars and planets. Current evidence fevers models. In which the primary component of dark matter is a new elementary particle. It is known as non-baryonic dark matter. The dark matter components have vastly more mass than the visible components of the universe.