Dark matter comprises 80% of the universe. Unfortunately, dark matter comprises 0% in a defunct gold mine in Lead, South Dakota. For three years and ten million dollars, scientists searched a mile underground with liquid xenon which would glow when certain dark matter particles reacted with the xenon. Alas, that didn't happen, but those involved in the project are eager to try again in a different location.

Source: http://phys.org/news/2016-07-scientists-invisible-dark.html

Image Source: By NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM). (http://www.spacetelescope.org/images/heic1014a/) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons