Astrophysicists believe as of now, that 25% of the matter and energy in our universe is ‘dark’ matter. Although this name sounds flashy, all it means is that this mass can’t be seen with light, like the ‘normal’ illuminated baryonic matter we are made of. Many experiments have been done that confirm dark matter’s indirect existence. The overwhelming evidence for dark matter comes from when one gravitationally analyzes the stars’ orbits and structure within our galaxy. After a complex analysis of several galaxies structure, one is forced to conclude that there is not enough baryonic matter to hold the galaxy together, and that its’ stars will just fly apart, destroying the structure we see. But, the data shows that although the matter we see is not enough to hold the stars together, the galaxies are still forming as if there is a ‘sphere’ of invisible matter dispersed throughout the galaxy and in between the stars. This is the dark matter, and so much of it is needed to hold the gravitational structure we see that there must be more of it than normal baryonic matter

Part of science, however, is finding theory that supports the existence of a new type of matter. Rather than consider this flaw a failure of our theory of gravity, which many physicists think it could be, scientists believe that there must be a theoretical particle that could explain this phenomenon. Its a very similar reasoning scientists took when they discovered the neutrino; rather than refute the laws of conservation of energy and momentum, Wolfgang Pauli proposed a weakly interacting particle that made up for this energy and momentum, and it turned out to actually exist. The best candidate for a dark matter particle as of now is called a WIMP, weakly interacting massive particle, which is similar to a neutrino in that it interacts vey weakly with normal matter, but it is much more massive that a neutrino, thus it is capable of creating the gravitational attraction we observe. Many projects have started that are trying to build WIMP detectors that could detect a WIMP very similar to how we detect neutrinos. Using underground mines and a large tank of xenon or other baryonic atoms that weakly interact with WIMPS, scientists predict how many WIMPS should interact on average with their detector based on how much dark matter passes through the earth all the time, and the signature of the interaction to prove if dark matter is really there. It will be very exciting to see how these experiments pan out.

Sources:

http://www.sciencedaily.com/releases/2014/03/140310212316.htm

http://en.wikipedia.org/wiki/Dark_matter

http://en.wikipedia.org/wiki/Neutrino