Dark matter is invisible object in space that is also called missing matter.
Dark matter can't be seen using visible, infrared rays or x-rays. The only way people know they are there is because of their mass. For the past 50 years, scientists have known that the activities of the various galaxies that make up the cluster of galaxies showed a mass 10 to 100 times the figure it would be if calculated merely by combining the amount of light each galaxy emits. In spiral galaxies, the mass calculated from revolving speeds is greater than merely adding up the number of stars it contains. Dark matter contributes to the extra mass of the galaxies and in turn the extra mass confirms the existence of the phenomena.