Galaxy seems to lack dark matter, stumping astronomers

Enlarge / The recently discovered galaxy is so diffuse that you can see other, more distant galaxies right through it. (credit: NASA, ESA, and P. van Dokkum)

Dark matter and galaxies normally go hand in hand. Dark matter seems to be needed to draw in sufficient material to form the galaxy and its stars, and halos of dark matter keep galaxies from spinning apart as they rotate. So scientists were more than a bit surprised to find a galaxy that has little to no dark matter at all. Confusing things further, the galaxy appears extremely similar to others that are nearly entirely composed of dark matter.

Slow motion

This was one of those cases where discovery began with the phrase "huh, that looks weird." The weirdness came courtesy of the Dragonfly Array, a collection of small telescopes designed to pick up faint objects. When observing a collection of galaxies called the NGC 1052 group, the array spotted an object that had shown up in other surveys of that region of the sky.

"It stood out to us because of the remarkable contrast between its appearance in Dragonfly images and Sloan Digital Sky Survey data," the authors of the paper describing the object write. Dragonfly saw it as a diffuse object with some structures in it; Sloan imaged it as a collection of distinct objects.