We all must have heard the name of Dark energy or Dark matter somewhere. We all know that dark matter is not visible and so is the dark energy so how do we know that they exist?
The discovery of dark energy dates back to the period of Albert Einstein. Einstein was ready with theory but it was not compatible with our assumptions of the universe . So he just removed some factors in order to make it right. Then came Edwin Hubble who observed exponential red shift and concluded that universe is expanding exponentially. And Einstein could introduce the factor in his equations which he omitted intentionally earlier.
The reason of the expanding of the universe is Vacuum energy which is also called Dark Energy. It the energy that binds all the stars together and makes their mass motion possible.
Next comes, Dark Matter. There is a very interesting phenomenon called Gravitational Lensing, in which lights from distant planets or galaxies gets bend because of the strong gravitational pull from the Dark Matter. It magnifies the image of the galaxies or stars for the observer and it is distinguishable from rest of the surroundings. Its like we bend light through lens.
This influence of dark matter on other things in the cosmos help us to do quantitative analysis of Black holes and other Dark matter.
So, this was the way by which we conclude the presence of dark matter in the space.
Still there are million mysteries that are to be unfold!