Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In modern cosmology one of the least understood phenomena in the universe is the so called dark matter. Dark dark matter is a currently unknown type of matter, hypothesized to constitute 84% of the matter in the universe and 23% of the mass-energy. However, as it neither emits nor absorbs light or other electromagnetic radiation, and so cannot be seen directly with telescopes. Learn more about dark matter, its properties and impact on cosmos in this book.