The Hubble Space Telescope has captured images of three odd galaxies that may help scientists solve a 13 billion-year cosmic mystery. The galaxies are so old and faint that astronomers nicknamed them “ghost galaxies” in a description. The objects are among the smallest and faintest galaxies near our own Milky Way galaxy, researchers said.

“These galaxies are fossils of the early universe: they have barely changed for 13 billion years,” scientists explained in an announcement. “The discovery could help explain the so-called ‘missing satellite’ problem, where only a handful of satellite galaxies have been found around the Milky Way, against the thousands that are predicted by theories.”