We might be making strides in mapping out or little corner of the Milky Way, but the universe still has more than a few mysteries left to keep us guessing. Case in point: a galaxy made up almost entirely of dark matter.
Dubbed Dragonfly 44, this mysterious galaxy is apparently made up of 99.9 percent dark matter. it’s roughly the same mass as our Milky Way, despite the fact that our galaxy has 100 times as many stars. Just let that sink in for a minute. That is one dense galaxy. The galaxy isn’t actually all that far away from Earth (in cosmic terms), but it’s so dim (see: dark matter) that it took until now for technology to reach a point where we could actually see it.
As Wired explaines, dark matter is essentially the “invisible gravitational glue” that holds galaxies together. It’s estimated to make up around five-sixths of the universe’s total mass, but finding this much of it crammed into one galaxy is a rare find. Once astronomers realized there had to be something unique about Dragonfly 44 to keep it from being ripped apart, they looked closer and realized it’s pretty much all dark matter.
Astronomers used the DEIMOS instrument installed on the WM Keck Observatory and the Gemini North Telescope in Manuakea, Hawaii, to measure the velocities of stars in the system for 33.5 hours over a period of six nights to estimate the galaxy’s mass. Put simply: The stars were moving as if the galaxy had way more mass than it should, so an abundance of dark matter is the only way to explain its existence.
Now, scientists hope to find another “dark galaxy” even closer to Earth (but not too close), so they can study it to try and figure out exactly what dark matter really is.
Check out the best shot we have of Dragonfly 44 below: