Ordinary gravity predicts that the raotational velocity should fall as one goes outwards in the galaxy. However, experimental observations show a flat rotation curve. This was the earliest evidence for dark matter halo.

Almost all of the universe is filled with unknown matter or energy. Matter, as we know it, comprises only approximately 5% of the universe. Rest of the universe is taken up by dark matter (∼1/4 of the total density) and dark energy (∼3/4 of the total density). One of the biggest questions in Physics now is: what is dark matter. Discovering the nature of the dark matter will not only solve a 70 year old mystery, but also will lead to the first solid evidence of supersymmetry manifesting itself outside of the high energy accelerators. The importance of searching for dark matter is evidenced in the sheer number of experiments all over the world directly searching for this illusive matter, be it axion on the lowest mass scale or Weakly Interacting Massive Particles (WIMPs) in the highest mass scale. LHC may beat the dark matter direct search experiments to seeing evidence of supersymmetry, by observing susperparticles, but the direct search experiment play the crucial role of confirming whether those super particles are indeed the dark matter of the universe.