What is Dark Matter What is dark matter?
This mysterious, apparently invisible stuff that researchers think is everywhere is not easily understood. A first step, however, is grasping what can be seen, and why. When a scientist peers into space, either through a standard telescope or with the aid of a fancy space-based observatory, the things she observes emit light energy, called electromagnetic radiation. Some of this radiation is optical — the visible light you see with your eyes. But this is just one type of light energy. Electromagnetic radiation comes in many wavelengths: radio waves (the longest), infrared, optical, ultraviolet, X-rays and short gamma rays (the shortest, and also the highest form of energy. See more details on these wavelengths at the bottom of this page). Galaxies, nebulae, stars, trees, microscopic bugs and anything else that can be observed glows with energy at one of these wavelengths. But in recent decades, researchers have become increasingly convinced that there is a vast amount of material in t
