Dragonfly 44 vs Milky Way: Why New Dark Galaxy Discovery Matters

A particularly dark galaxy has been discovered. Scientists are referring to it as a “dark” Milky Way.

The galaxy was found using one of the world’s most powerful telescopes after a team of astronomers analyzed the velocity of stars for over six nights, Space Daily reported Monday. The celestial formation, known as Dragonfly 44, is so dark because it is primarily made up of dark matter, a paper published last week in Astrophysical Journal Letters stated.

“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," Pieter van Dokkum, an astronomer at Yale University and lead author of the paper, said.

Dark matter is an invisible substance that scientists theorize makes up as much about 85 percent of all matter in the observable Universe. Since it cannot be “seen” in conventional ways, researchers have relied on mapping out the impact the substance has on visible objects. Dragonfly 44 — which is 330 million light-years away from Earth — is the latest indicator that scientists are on the right track to proving dark matter’s existence.

Van Dokkum and his team observed the galaxy from the W.M. Keck Observatory and the Gemini North telescopes in Hawaii. While they watched the stars and their interaction, they were hoping to determine the galaxy’s mass based on the velocity of the visible objects. The faster the stars moved, according to the researchers, the more mass the galaxy would have.

“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,” Roberto Abraham, an astronomer from the University of Toronto and a co-author of the paper, said.

So, how big is the dim galaxy? The researchers estimate that it is roughly one trillion times the mass of the Sun, similar to that of the Milky Way. Just 0.01 percent of that mass comes from visible stars, however, and 99.99 percent is dark matter.