What dark matter really is ?

Although dark matter has not been directly observed, its existence and properties are inferred from its gravitational effects such as the motions of baryonic matter, gravitational lensing, its influence on the universe's large-scale structure, on the formation of galaxies, and its effects on the cosmic microwave background.

https://steemitimages.com/DQmSbju2hJWysfE4kBhwtr3vWJ113ivA6odneTGezbsBJwi/dark-matter-energy-atoms-pie-chart-NASA-e1411130628194.png
According to the most accepted theories of the universe, dark energy is thought to contribute 73 percent of all the energy, which leaves only 4 percent of the universe composed of regular matter, such as stars, planets and people. Pie chart via NASA.

The standard model of cosmology indicates that the total mass–energy of the universe contains 4.6% ordinary matter, 24% dark matter and 71.4% dark energy. Thus, dark matter constitutes 84.5% of total mass, while dark energy plus dark matter constitute 95.1% of total mass–energy content. The great majority of ordinary matter in the universe is also unseen. Visible stars and gas inside galaxies and clusters account for less than 10% of the ordinary matter contribution to the mass-energy density of the universe.

The most widely accepted hypothesis on the form for dark matter is that it is composed of weakly interacting massive particles (WIMPs) that interact only through gravity and the weak force. The dark matter hypothesis plays a central role in current modeling of cosmic structure formation, galaxy formation and evolution, and on explanations of the anisotropies observed in the cosmic microwave background (CMB). All these lines of evidence suggest that galaxies, galaxy clusters, and the universe as a whole contain far more matter than that which is observable via electromagnetic signals. Many experiments to detect proposed dark matter particles through non-gravitational means are under way; however, no dark matter particle has been conclusively identified.

Although the existence of dark matter is generally accepted by most of the astronomical community, a minority of astronomers, motivated by the lack of conclusive identification of dark matter, or by observations that don't fit the model, argue for various modifications of the standard laws of general relativity, such as MOND, TeVeS, and conformal gravity that attempt to account for the observations without invoking additional matter.

Difference between dark matter and dark energy......

Dark matter and dark energy are the yin and yang of the cosmos. Dark matter produces an attractive force (gravity), while dark energy produces a repulsive force (antigravity). Together, they make up 96 percent of the universe—and we can’t see either. Astronomers know dark matter exists because visible matter doesn’t have enough gravitational muster to hold galaxies together. What’s it made of? There are two adorably acronymed leading candidates: super-dense astronomical bodies called massive astrophysical compact halo objects (MACHOs) and weakly interacting massive particles (WIMPs). Dark energy, on the other hand, is why our universe is expanding. In fact, in 1998, astronomers studying distant supernovae were shocked to learn that, around 7.5 billion years after the Big Bang, the universe began expanding faster. That indicates some unknown force is fighting gravity’s pull, causing galaxies to speed apart from one another. Think of the universe as an elastic gym band and dark energy as the Incredible (and unseen) Hulk who keeps tugging at it

Dark matter is a hypothetical type of matter distinct from baryonic matter (ordinary matter such as protons and neutrons), neutrinos and dark energy.

Dark matter has never been directly observed; however, its existence would explain a number of otherwise puzzling astronomical observations. The name refers to the fact that it does not emit or interact with observable electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum.

The dark matter problem can also be viewed as a question of the nature of clustering matter. Dark matter must be the basic building block of the largest structures in the universe: galaxies and clusters. Without dark matter, the universe would be a very different place, according to current theories.
https://steemitimages.com/DQmRL3MrzeyTXsR7DorumTPhuMeFvnQhEjxLPdt8MH5n1Nx/dark-matter-filaments-false-color-Epps-Hudson-2017-e1492027036449.jpg
Dark matter filaments bridge the space between galaxies in this false-color map. The locations of bright galaxies are shown by the white regions and the presence of a dark matter filament bridging the galaxies is shown in red. Image via RAS/ S. Epps & M. Hudson / University of Waterloo.

And dark matter is not just for explaining the behavior of distant bodies in the cosmos, but is abundant within our galaxy as well. It is estimated that our solar system is passing through a fine sea of dark matter particles with a density as high as roughly 105 per cubic meter. We may hope to detect the flux of dark matter passing though the Earth, and even to detect the seasons of dark matter, corresponding to the times of year when the Earth is moving with, or against, the flow of dark matter orbiting the center of the Milky Way. Dark energy, on the other hand, originates from our efforts to understand the observed accelerated expansion of the universe.

How dark matter is going to affect our universe?????

In a nutshell, current theory cannot explain the acceleration. One speculative possibility is that the acceleration is a consequence of another new form of matter, nicknamed dark energy, which has hitherto gone undetected. It is called "dark" because it must necessarily be very weakly interacting with regular matter--much like dark matter--and it is referred to as energy because one of the few things we are certain of is that it contributes nearly 70 percent of the total energy of the universe. If we can figure out what it really is, it is certain we will find a more illuminating name.
Refrences
https://en.m.wikipedia.org/wiki/Dark_matter

http://earthsky.org/space/waterloo-image-dark-matter-cosmic-web-2017

http://mentalfloss.com/article/68083/whats-difference-between-dark-matter-and-dark-energy

https://www.scientificamerican.com/article/what-are-dark-matter-and/
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