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Hubble, Euclid and Subaru Reveal Ultra-Faint Galaxy Candidate Dominated by Dark Matter

Stacked images around four tightly grouped globular clusters expose CDG-2’s diffuse starlight, making it the strongest dark‑galaxy candidate reported.

Credit: NASA, ESA, D. Li (Utoronto), Image Processing: J. DePasquale (STScI)
This deep space image taken by NASA's Hubble Space Telescope contains CDG-2, a dark matter-dominated galaxy.
Image
CDG-2 (dashed red circle) is dominated by dark matter and contains only a sparse scattering of stars. Image credit: NASA / ESA / Dayi Li, UToronto / Joseph DePasquale, STScI.

Overview

  • Combined Hubble, Euclid and Subaru observations reveal extremely faint diffuse light around four globular clusters in the Perseus cluster, supporting a bound galaxy.
  • Preliminary analysis indicates roughly 99% of CDG-2’s mass is dark matter, with the clusters contributing about 16% of its visible light.
  • Estimates put its luminosity at only a few million Sun-like stars and its distance in the 240–300 million light‑year range, reflecting minor reporting differences.
  • This object is the first galaxy identified solely through its globular cluster population, validating a search technique for nearly invisible systems.
  • Researchers propose that interactions in the dense cluster likely stripped star‑forming gas, and they call for kinematic and spectroscopic follow‑up to refine key measurements.