Some 60 million light-years from Earth, not too far from our local galactic neighborhood, a strange little galaxy is causing a cosmic stir. This little island universe holds far fewer stars than your average galaxy. But it’s not the lack of stars that’s surprising astronomers. The galaxy, nicknamed DF2, also seems to lack any significant amount of dark matter.
Because DF2 would be the very first known galaxy without the mysterious substance, the news of its discovery in 2018 quickly spread throughout the astronomical community. If confirmed, a galaxy without dark matter would throw a wrench into our understanding of how galaxies form and evolve. Every galaxy we know of so far has a sizeable chunk of the invisible matter, so finding one without it would mean one of two things: Either DF2 never had any dark matter to begin with, or it somehow managed to shed its dark matter during the course of its life.
But extraordinary claims require extraordinary evidence. And according to at least one group of researchers, the evidence for DF2’s dark-matter deficiency doesn’t hold up.
