Astronomers using the Hubble Space Telescope have discovered a highly unusual object dubbed Cloud-9: a dark, diffuse, and enormous object that researchers classify as a "failed galaxy" — a system that accumulated a dark matter halo and began forming stars early in the universe but then lost the gas needed to grow further, leaving behind a ghostly relic unlike any previously catalogued object.
Cloud-9 has an extremely low surface brightness, no discernible central concentration of older stars, and a highly unusual dark matter distribution. Unlike typical dwarf galaxies, it shows no clear nucleus or spiral structure. Its sheer size sets it further apart — the object spans a region far larger than would be expected for the small number of stars it contains.
A New Class of Object
A failed galaxy is thought to be a system that accumulated a dark matter halo and a modest amount of gas but never successfully ignited the sustained star formation needed to grow into a normal galaxy. Cloud-9 appears to have formed stars briefly in the early universe before something — possibly early ultraviolet radiation from nearby quasars, or gravitational tidal stripping — shut that process down permanently.
The discovery challenges existing computer models of galaxy evolution, which struggle to account for objects that persist in a state between truly starless dark matter halos and fully developed galaxies. How Cloud-9 survived for billions of years without merging or dispersing remains an open question.