The Solar System
In Cosmological terms, dark matter is a hypothetical entity which doesn�t give out or reflect sufficient amounts of electromagnetic radiation to be observed directly. Their presence is inferred from the gravitational pull which they inflict on objects around them. Their composition is still a mystery but it hypothesizes to contain heavy neutrinos, axions and WIMPs. The conventional matter in the universe which makes the stars, life, air and planets accounts for only a tiny percentage of what is supposed to be exist. This is based on the fact, that without the additional source of gravity, galaxies would be flying apart from each other. No one knows where this supplementary gravity originates from, so there must be some kind of invisible stuff there which they call dark matter. The anatomy of the universe is believed to be as 5% normal matter, 25% dark matter and 70% dark energy. Dark energy is a still more bizarre entity, it�s perceived to be some sort of energy which is capable of beating gravity and is responsible for the expansion of the universe at a faster rate.
Proof of Presence
Some astronomers believe that we are merely trying to cover up our ignorance of the true ways of gravity by invoking dark matter. Perhaps, our notions of gravity are wrong and it doesn�t work in the same way as Newton and Einstein predicted when it comes to intergalactic scales. Astronomers agree that the idea that the universe is filled with dark energy seems at best crazy and at worst totally preposterous. A team of scientists led by Doug Clowe of University of Arizona at Tucson decided to set rest to all speculations about dark matter once and for all. Clowe and his team used NASA�s Chandra X-ray Observatory and studied the galaxy cluster 1E0657-556 which features a bullet shaped superheated gas cloud. X-rays revealed that the peculiar shape was created due to cosmic winds which are generated due to high-speed collision between two cluster galaxies. The team brought in other telescopes to measure the amount of mass within the clusters. They were able to measure effect of gravitational lensing, which is the phenomenon by which the gravity is able to bend light emitted from thousands of background galaxies, as Einstein stated in his Theory of Relativity. The dark matter was never seen, but its gravitational effects rendered a predictable effect on the outcome. The image reveals that the normal matter was slugged down by a drag force, cosmic analogous to air resistance. However, the dark matter was unaffected by the drag force, this means that dark matter doesn�t interact with normal matter, which further bolsters the theory.
Cosmological models predict that if dark matter is really made of WIMP, then trillions of them must be passing through earth each second. Unfortunately, despite numerous attempts to detect WIMPS, none have been found. One possible alternative is to artificially produce WIMP�s in the lab, especially massive scale experiments such as Large Hadron Collider in Geneva. Since WIMP�s are known to have negligible interaction with matter, a segment of missing momentum or energy usually indicates the presence of a WIMP.