About Dark Matter:
Dark Matter, in astronomy, designation for matter that does not give off or reflect detectable electromagnetic radiation, the radiant energy that includes visible light, radio waves, infrared radiation, X rays, and gamma rays. Although dark matter is practically invisible, astrophysicists have determined its existence by detecting its gravitational interaction with matter that does give off detectable electromagnetic radiation, such as stars, galaxies, and clusters of galaxies. Dark matter has become a vital component of modern theories of cosmology and elementary particle physics. Along with the phenomenon of dark energy, the puzzle of what dark matter is represents one of the most important questions in physics today.
What is it anyway ?
To gain a fuller understanding of our universe, it is vital to determine exactly what dark matter is made of. Scientists think that dark matter occurs in several different forms. Moreover, observations and experiments place limits on the quantity and distribution of each type. There are two broad categories of dark matter: “hot” dark matter, which moves at speeds comparable to the speed of light (about 299,000 km per second or 186,000 mi per second), and “cold” dark matter, which moves at speeds well below that of light.