A new galaxy that is as big as the Milky Way has got one amazing secret: it is almost entirely composed of dark matter, the mysterious substance that scientists believe makes up most of our universe but that we know little about. Scientists think this galaxy is 99.99 percent dark matter, with just a hundredth of a percent being the typical matter we would be able to see and interact with.

It’s a fascinating finding, because there is so little we know about dark matter. The only reason we know it exists is because it has gravity. Scientists believe that about 80 percent of all the mass in the universe is dark matter.

The galaxy is named Dragonfly 44 and it was first detected last year using the Dragonfly Telephoto Array in New Mexico. The galaxy is one of 47 “fluffy” galaxies in the Coma Cluster, which is 300 million light-years from Earth. But despite it being well within the range of telescopes like the Hubble Space Telescope, no one had noticed them until the Dragonfly telescope was trained on them because they only emit a tiny fraction of the light of the Milky Way despite being the same size.

“Very soon after its discovery, we realized this galaxy had to be more than meets the eye. It has so few stars that it would quickly be ripped apart unless something was holding it together,” said Yale University astronomer Pieter van Dokkum, lead author of a paper in the Astrophysical Journal Letters.

“Amazingly, the stars move at velocities that are far greater than expected for such a dim galaxy. It means that Dragonfly 44 has a huge amount of unseen mass,” said co-author Roberto Abraham of the University of Toronto.