Cloud-9 is an extragalactic cloud of neutral atomic hydrogen (HI) in the vicinity
of the galaxyM94 (Messier 94 aka NGC 4736).
Lack of stars in the region led to the theory that it
is an example of a galaxy without stars.
Cloud-9 was discovered by FAST, which detected
its 21-cm line in 2023,
the discovery then confirmed by the Very Large Array and Green Bank Telescope.
The density of the cloud suggests there is much more mass than
the indicated HI, evidence for enough dark matter to hold it together,
counteracting the gas's pressure.
Existing visiblesurveys had not
previously detected a galaxy or stars at that location,
suggesting it could be a star-less galaxy.
HST observations in 2025 performed a more thorough
search for such stars or for a diffuse visible galaxy,
and none were found, supporting the notion.
I believe the name Cloud-9 stems from a survey of clouds
adjacent to M94, which numbered the cloud candidates it observed.