Cloud-9: Hubble finds a starless, dark-matter-dominated hydrogen cloud

Hubble observations show Cloud-9 is a starless neutral-hydrogen cloud about 4,900 light‑years across with an inferred dark matter mass near five billion suns.

NASA and partner teams report the identification of a starless, gas-rich object nicknamed Cloud-9. Classified as a Reionization-Limited H I Cloud (RELHIC), it is described as a primordial neutral-hydrogen structure that has not formed stars. Radio observations first detected the hydrogen signal in 2023 near the spiral galaxy Messier‑94, about 14 million light‑years away, and Hubble's Advanced Camera for Surveys was used to search for starlight. The Hubble images showed no detectable stars, leading researchers to infer a dark-matter-dominated halo. Key details: - Cloud-9 spans roughly 4,900 light‑years across and contains about one million solar masses of neutral hydrogen. - Analysis indicates an inferred dark matter mass near five billion solar masses, which would provide the gravitational binding for the cloud. - Deep Hubble imaging revealed no detectable stellar population, and injected-signal simulations indicate the telescope would have seen even a faint population if present. - The object is described as a RELHIC (Reionization-Limited H I Cloud), a theoretical early-universe, starless gas halo that has not ignited star formation. - The research team includes Alejandro Benitez-Llambay (Milano‑Bicocca), lead author Gagandeep Anand (Space Telescope Science Institute), and co-author Andrew Fox (AURA/STScI/ESA); results appear in The Astrophysical Journal Letters. Summary: The finding provides a nearby example of a dark-matter-dominated, starless hydrogen cloud that aligns with theoretical predictions of "failed" or non-star-forming galaxy halos. Undetermined at this time.