Dark Matter

Dark matter is a hypothetical form of matter that is thought to account for approximately 85% of the matter in the universe, and about a quarter of its total energy density. The majority of dark matter is thought to be non-baryonic in nature, possibly being composed of some as-yet undiscovered subatomic particles.

Non baryonic matter signifies the matter which is not made up of baryons i.e., protons and neutrons.

The theory of dark matter is a very weird thing but yet the scientists believe that it exists. This is because of large amount of evidence we have which favors the existence of dark matter.

Some of which are:

1. Galactic Rotational Curves

As I discussed in my previous article about how the theoretical rotational curves look like. From standard Newtonian dynamics, we expect the velocity of stars to fall as you move away the center of mass of a galaxy towards its outer edges. But when studying the Andromeda galaxy in the 1960s, Vera Rubin and Kent Ford found something very different: the velocity of stars remained approximately constant, regardless of how far they were from the galactic center.

The observed rotational curve looked like this :

This signifies that as we move away from the galaxy, the mass keeps on increasing. This is not possible on account of Visible matter. Thus dark matter theory came up.

2. Galaxy Clusters

In 1933, Fritz Zwicky (below) was studying the nearest very large cluster of galaxies to us in space: the Coma cluster. Using Newtons Laws of Motion he determined that the galaxies were moving much faster than they should and the visible matter is not enough to keep the galaxy bound.

3. Gravitational Lensing

The mass calculated using gravitational lensing is much more than the visible matter.

4. Not enough Baryons

When the amount of baryonic particles formed after the Big Bang was calculated, it was observed that the calculated amount of particles could not lead to the observed mass of the universe. Thus matter formed of particles other than protons and neutrons was theorized.

All of this leads to prominent evidence for existence of dark matter. The Large Hadron Collider is working for to find dark matter.