Dark matter in space : The 'missing mass' in galaxies

What is dark matter in space?

Everything you need to know about Dark Matter 

Our universe is serving as the host of a variety of celestial entities for over 13 billion years. Again, 200,000 years ago, the first human civilizations began and so did our exploration of our very own universe. Until now, we have found about 100 million galaxies and about 200 billion stars associated with these galaxies. But it's mind-blowing that all of these observable objects out there in the universe constitute only up to 5% of the total universe? Experts claim that only 5% of the matter is actually observable in the universe, and the rest 95% is filled with 'void'. To be more clear, it's filled with dark matter and dark energy.

What is Dark matter?

Dark matter, just like its name suggests, is completely dark. And not just by its appearance, its properties and behaviour are just as mysterious and dark. Dark matter was first discovered as the missing mass in galaxy clusters, which was noted when scientists noticed the irregularity in the orbital velocity of the stars that were orbiting these galaxy clusters. They later found out that this was caused because these clusters were possessing much more mass than the observable mass within them and that this matter was actually residing between the galaxies. Dark matter in space only interacts with ordinary matter via gravity.

This matter is very difficult to observe and doesn't show any sign of its existence, such as radiation or absorption. That's because dark matter doesn't emit, absorb or interact with electromagnetic radiation or any of the ordinary matter out there. And hence its name befell as, 'dark matter.'

Even though we can't directly detect this dark matter, its effects like gravitational lensing of distant galaxies are observable. Gravitational lensing is the phenomenon where the light that comes from a distant light source (eg. galaxy), will be bend by the dark matter that was present along its path. This matter will act as a lens to the observer who views the distant galaxy and thus the light rays get distorted and the image will appear magnified. The presence of dark matter in galaxies is the one reason why fast-moving stars don't fly away from the gravitational field of the galaxy.

But because it possesses such an introverted and mysterious behaviour, there isn't enough data or observations which reveal the constituents of dark matter. Scientists have various theories as candidates, like the Weakly Interacting Massive Particles (WIMPs), which are non-baryonic matter (matter that isn't made of protons, neutrons or any other ordinary matter) but is still not proven yet. Whatever that constituent is, it's not something that we've known about or heard of. 

Dark energy is just as mysterious as dark matter, if anything, more mysterious than the latter. Dark energy is that force that is responsible for the rapid expansion of the universe. But there is no explanation on what basis does dark energy exists or from where it comes from.