Credit: (Images by Pieter van Dokkum, Roberto Abraham, Gemini, Sloan Digital Sky Survey)
The dark galaxy Dragonfly 44. The image on the left is from the Sloan Digital Sky Survey. Only a faint smudge is visible. The image on the right is a long exposure with the Gemini telescope, revealing a large, elongated object. Dragonfly 44 is very faint for its mass and consists almost entirely of dark matter.