It was in 1930s when Fritz Zwicky observed that many galaxies were moving faster than theoretical calculations. This implied that there was some mysterious gravitational pull towards the centre of those galaxies. The quantity of matter needed to exert such a pull far exceed the observed matter. This extra matter which invisible and undetected has been termed as Dark Matter.
Gradually many astronomers started researching on dark matter. It was when the Andromeda Galaxy was observed to be moving faster than expected that dark matter took the centre stage of astronomical research.
It has not yet been observed yet directly. It doesn’t interact with matter and is completely invisible to light and other forms of electromagnetic radiation making it impossible to detect.
Scientists are confident it exists because of the
gravitational effects it has on galaxies and galaxy clusters. The light from distant galaxies gets distorted and magnified by massive, invisible clouds of dark matter in the phenomenon known as Gravitational Lensing.
There are two schools of thoughts on the existence of Dark Matter. While one school supports the idea of MACHOS (MAssive Compact Halo ObjectS) the other advocated WIMPS (Weakly Interacting Massive ParticleS). MACHOS are made up of Baryons (protons and neutrons) while WIMPS consists of Exotic particles which in turn are non-baryonic.
Dark matter responds to 2 of the Fundamental Forces: Weak Nuclear Force and Gravitational Force.