A Galaxy Composed Almost Entirely of Dark Matter Has Been Confirmed

Wired

by Jorge Garay

February 20, 2026

AI-Generated Deep Dive Summary

Astronomers have identified a rare cosmic phenomenon: a galaxy composed almost entirely of dark matter. Designated as CDG-2 (Candidate Dark Galaxy-2), this faint system lies approximately 300 million light-years away in the Perseus cluster. Initially mistaken for four separate globular clusters, CDG-2 is now confirmed to be a single galaxy where up to 99.9 percent of its mass is dark matter, with only about 0.1 percent composed of visible stars and other conventional matter. The discovery was made possible through data from the Hubble, Euclid, and Subaru telescopes, which revealed an extremely faint glow surrounding the four globular clusters previously thought to be independent objects. This residual light indicates a gravitationally bound system with a dense dark matter halo. CDG-2's total luminosity is equivalent to about 6 million suns, with the globular clusters contributing just 16 percent of its brightness—a disproportionately large share that suggests an unusually massive and invisible dark matter structure. Dark matter, which makes up roughly 27 percent of the universe’s energy density and 85 percent of its matter, remains one of the greatest mysteries in astrophysics. While it does not emit or reflect light, its gravitational effects are evident in the motion of stars and galaxies, including our own Milky Way, which is estimated to be composed of about 90 percent dark matter. However, CDG-2 represents an extreme case: a galaxy with almost no visible stars, yet dominated by an invisible halo of dark matter. Such "dark galaxies" are exceedingly rare but provide invaluable insights into the nature of dark matter and galaxy formation. As natural laboratories for testing current models, they challenge scientists to better understand the role of dark matter in shaping cosmic structures. The study of CDG-2 could also pave the way for new technologies and methods in space exploration, offering a deeper understanding of the universe's hidden mass and its implications for the stability of galaxies and systems like our own. This breakthrough not only advances astrophysics but also holds significance for readers interested in tech, as it pushes the boundaries of what we know about the universe’s fundamental makeup. By unraveling the mysteries of dark matter, scientists may unlock new possibilities for technology that could revolutionize how we observe and interact with space.

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Originally published on Wired on 2/20/2026