In 2015, scientists detected a strange galaxy just about the same size as the Milky Way. Dragonfly 44 is known as the "dark twin" of the Milky Way because it is made up of 99.99% dark matter. Dark matter is... well, no one quite knows what it is. The best understanding we have is that it's an invisible substance that makes up 80% of mass in the universe. Scientists know that dark matter exists because they can see the effects of it in gravity and on the weight of galaxies.
Only one-hundredth of one percent of the Dragonfly 44 galaxy is visible matter. But by using the Dragonfly Telephoto Array telescope in New Mexico, scientists were able to detect the galaxy in 2015. The array, which has eight telephoto lenses and cameras, was designed to detect things in space too dim to see with other telescopes. When scientists first observed Dragonfly 44, they thought it must not be as large as it is, because it has so few stars, but they ultimately concluded that it must be dark matter holding the dark mysterious galaxy together. Learn more about Dragonfly 44 in the video below.