NASA and ESA Confirm CDG-2 as a Dark Galaxy

More on Candidate Dark Galaxy Two (CDG-2) from ESA

From Google AI:

Candidate Dark Galaxy One (CDG-1) is a rare, low-surface-brightness system in the Perseus cluster, identified as a tight, isolated grouping of four globular clusters lacking visible, diffuse stellar light. Detected via Hubble Space Telescope imaging, CDG-1 represents a potential candidate for a nearly-dark galaxy where stellar emission is almost entirely absent.

• Discovery and Characteristics: CDG-1 was discovered in the Perseus galaxy cluster as a grouping of 4 potential globular clusters without any associated diffuse, starlight-emitting galaxy.
• Observations: Hubble Space Telescope (HST) UVIS F200LP imaging found no detectable diffuse emission, setting a surface brightness limit of > 28.1 mag arcsec, which suggests a high likelihood that the light from the system is almost entirely concentrated in the clusters themselves.
• Nature: It is characterized as a "nearly-dark" or low-surface-brightness dwarf galaxy.
• Alternative Explanation: A less likely possibility is that it represents a chance alignment of four unrelated globular clusters within the halo of a larger galaxy (IC 312).

It should not be confused with CDG-2, a subsequently identified "ghost galaxy" (reported in 2025/2026) in the same cluster, which was discovered with a faint, diffuse, and extremely dark-matter-dominated, low-surface-brightness stellar component.