What is dark matter?

Observations of how stars rotate around galaxies produced a problem. The visible matter in the galaxy is not enough to explain the way the stars orbit the galaxy. Additional mass is required to explain this.

In fact ordinary matter is now thought to account for only about 5% of the mass-energy in the universe. The rest is thought to be dark matter and dark energy.

Dark energy is another theoretical concept which explains the expansion of the universe.

Dark matter was devised to account for much of the missing mass in the universe. It doesn't interact with normal matter except through gravity and possibly the weak force.

(In the photo, the arc or lensing effect is caused due to Dark matter.)

The most accepted theory is that dark mater consists of as yet undiscovered particles such as Weakly Interacting Massive Particles (WIMPs). There is as yet no evidence of any such particle.

Some physicists are attempting to eliminate the need for dark matter by modifying our laws of physics to explain the orbits of stars in large structures such as galaxies.

Another theory, which I particularly like, is that dark matter is made up of black holes.

Dark matter is a theoretical concept which stands as an answer to the inexplicable astronomical behaviours or phenomena.

It does not interact with electromagnetic forces, therefore, light is not emitted nor absorbed.

Dark matter is thought to make up 27% (approx.) of the universe

It can be 'detected' by its gravitational influence on other celestial objects.

Moreover, dark energy is 'proportional' to the space-time frame, so it increases throughout the expanding universe. (which is accelerated by this hypothetical type of energy).

It accounts for nearly 68% of the universe.

The expansion & acceleration rate is measured by the Hubble's law applications. #(≈ 70"km"/h# or #19.445 m/s#)

As the name suggests, "Dark matter" is dark, it can't been seen because it doesn't interact with light.

Dark matter is more a theoretical concept that explains "why galaxies in our universe in such structure though normal matter's gravity isn't strong enough to hold up galaxy?"

We know that galaxies are spinning and as you could guess, if gravitation pull isn't strong enough, the stars or planets or other celestial bodies might be thrown out.

Here's where the dark matter's role comes into play. Dark matter makes up nearly #27%# of our universe. Dark matter helps to hold up galaxy together.

But how do we know that such stuff exists?
Well, at some regions where such kind of "stuff" is present in high density, light bends from its path and so we conclude that something invisible exists there...