Dark Matter

 ~Anvi Patil(Xth A Abhinav Vidyalay)

In the universe, there is about 25% of dark matter and 70% of dark energy but only 5% of it is visible.

What is Dark Matter?

It is a non-luminous material, which holds two galaxies. This cannot be called a black hole because it does not bend light.

Then the question arrives, as it is non-luminous, how did we detect it?

As it is not visible, scientists have found indirect methods to find more about it. One such method is by using the Fermi Gamma-Ray Space Telescope. Gamma rays are released when two particles of dark matter collide, Fermi telescope can be used to detect this collision.

This topic was discovered by Fritz Zwicky in the 1930s, he discovered that galaxies were rotating at a faster rate than usual.

A dark region seen in the foreground of a star field. This dark region could be a dark cloud of gases like hydrogen, left over from the formation of our galaxy

Dark matter is called ‘dark’ not because it is ‘black’ but because it does not interact with electromagnetic fields i.e. it does not absorb, emit or reflect electromagnetic radiation, therefore making it difficult to detect.

In the 1600s Johannes Kepler discovered that if the planet is far from the sun, it orbits slowly. An astronomer, Vera Rubin, thought that nebulae also move in a similar pattern as that of the solar system.

She found that the speed is even faster on the outskirts of the galaxies. there is very less count of stars on the outside of galaxies. if there was more matter, then only there was a way to make the equations work. This was named dark matter.

There are many theories about Dark Matter. Some say it doesn't exist. Others say it consists of black holes, brown dwarfs, and neutron stars. It could be small subatomic particles that don't react with normal matter. Some say that it has more speed than light, which makes them extremely hot.

Also, it has been proven that it moves slower than the speed of light. Dark matter is classified as cold, warm, or hot according to its velocity.

The next theory can be appropriate. Dark Matter is made of axions. It can be said that as axioms show similar properties as dark matter they do not emit light or do interact with normal matter.

The most appropriate theory according to me is massive astrophysical compact halo objects (MACHOs). This theory says that dark matter includes black holes, neutron stars, and brown dwarfs. As they cannot be detected using typical methods (because they emit little or no radiation)  they are observed by studying light from distant stars through a process known as microlensing. Due to their immense mass, MACHOs bend and focus rays of light around themselves, which causes the rays to appear brighter. The level of distortion depends on the mass of the MACHO. By observing the light, scientists are able to calculate the amount of hidden matter present.

To conclude, Dark matter is still a mystery. We cannot follow any theories as they can only define visible matter (about 5%). Soon enough new things will be discovered.

Thank you for reading!

Edited By - Hemal Dedhia and Arya Dharmadhikari

Image credit:

1st Image

2nd Image

3rd Image

Editor's Note:

Essentially Dark Matter (DM) is called so because it is some material that doesn't interact with light. You see a cat on the road because the molecules of the cat's fur, send the light falling on them, back to you. DM molecules (or particles) do not. Light simply passes by.

Hot DM is not made of particles "faster" than light (such particles are called Tachyons) but simply particles going close to the speed of light. One candidate for HDM is the neutrino.

The most accepted model for DM is CDM - Cold dark matter - which could be made of bizarre particles like the axions or axinos and so on. If we try to create the universe mathematically from its beginning to date, we find that assuming CDM gives us the most accurate description of the current universe.

We haven't found ANY of these candidates to either exist or to explain the entire universe, YET. Hence the alternative theory is that Dark Matter, Doesn't Matter. It is simply a mistake in the Einstein equations that we use to construct the universe. OR it is simply the huge amount of Hydrogen left over from the universe's formation which is invisible to our telescopes.

keep looking folks