In the last century, astronomers studying the motions of galaxies and the character of the cosmic microwave background radiation came to realize that most of the matter in the universe was not visible. About 84% of the matter in the cosmos is dark, emitting neither light nor any other known kind of radiation. Hence it is called dark matter. One of its other primary qualities is that it only interacts with other matter via gravity: it carries no electromagnetic charge, for example. Dark matter is also “dark” because it is mysterious: it is not composed of atoms or their usual constituents like electrons and protons. Particle physicists have imagined new kinds of matter, consistent with the known laws of the universe, but so far none has been detected or its existence confirmed. The Large Hadron Collider’s discovery of the Higgs boson in 2012 prompted a burst of optimism that dark matter particles would soon be discovered, but so far none has been seen and previously promising classes of particles now seem to be long-shots.
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Source: Phys.org