Astronomers have identified CDG-2, a faint galaxy in the Perseus cluster that appears to be composed almost entirely of dark matter. Located 300 million light-years from Earth, it was discovered by tracking globular star clusters using data from Hubble, Euclid, and Subaru telescopes. Scientists estimate that about 99% of its total mass is dark matter.​Astronomers have identified CDG-2, a faint galaxy in the Perseus cluster that appears to be composed almost entirely of dark matter. Located 300 million light-years from Earth, it was discovered by tracking globular star clusters using data from Hubble, Euclid, and Subaru telescopes. Scientists estimate that about 99% of its total mass is dark matter.  ​ science