How was the presumed dark matter of the Universe calculated and what kind of an entity is it?

Answer 1

Dark matter refers to matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation (light) to be detected directly, but whose presence may be inferred from gravitational effects on visible matter such as stars and galaxies. i do not know how it is calculated, but it supposedly makes up about 22% of the total energy density of the universe.
The Bullet cluster is the best current evidence for the nature of dark matter.

Answer 2

The dark matter present in this universe are detected either by X-ray telescopes (if it emits X-rays) or by using a technique called gravitational lensing. According to this technique, the light from a star behind the dark matter will be bent by its gravitational force. After analysing the light, the presence of the dark matter will be confirmed.

Answer 3

The outermost stars in observed galaxies are moving too fast. If there were not more matter than we can see in the galaxy then these outer stars would not stay in the galaxy, they would spin off. Therefore "dark matter", matter that we connot see, is postulated to be there to make up the needed gravity.

Answer 4

It was calculated based on its gravitational effects on observable matter. The current dominant theory is that it is largely composed of particles that do not interact via electromagnetism (which is how we detect most particles), which we call WIMPs for "weakly interacting massive particles." Another theory is that it is made up of large celestial bodies that emit very little radiation, called MACHOs for "massive compact halo objects."