Astronomers may have found one of the clearest examples yet of a strange type of cosmic object that appears to contain gas and dark matter—but almost no stars.
The object, known as Cloud-9, has been studied for several years because it looks different from an ordinary galaxy. Located near the spiral galaxy M94, about 15 million light-years from Earth, Cloud-9 contains a huge amount of hydrogen gas but has shown no obvious evidence of stars.
Now, new ultra-deep observations have taken the mystery a step further. Researchers searched the object with one of the world's largest optical telescopes and found no detectable starlight across its central region.
The findings, described in a paper posted to the arXiv preprint server on August 21, could make Cloud-9 one of the strongest candidates yet for a starless or "dark" galaxy.
A Galaxy Without Stars?
When we think about a galaxy, we usually imagine billions of stars surrounded by gas, dust and dark matter. But cosmological theories suggest that not every dark matter structure in the universe necessarily becomes a normal, star-filled galaxy.
The widely accepted Lambda Cold Dark Matter (ΛCDM) model predicts that the universe should contain enormous numbers of relatively small concentrations, or halos, of dark matter.
These halos can attract gas through gravity. However, under certain conditions, the gas may never become dense and cold enough to collapse and create stars.
One reason is the competition between several processes.
Gravity tries to pull the gas together. At the same time, the gas can heat and cool, while ultraviolet radiation spread throughout the universe can provide additional heating. This background radiation comes from energetic sources such as quasars and stars.
In small dark matter halos, these effects may prevent the gas from becoming sufficiently concentrated to start star formation.
If such an object exists, it would essentially be a dark matter and gas system without a normal stellar population.
Finding one would therefore be important. It would provide an opportunity to test a major prediction of modern cosmology.
Why Cloud-9 Is So Interesting
Cloud-9 is particularly interesting because it already appears to have many of the characteristics expected from such an object.
It is a large cloud of neutral hydrogen, known as HI, located near M94. The system is estimated to contain approximately 1 million times the mass of the Sun in hydrogen gas.
Yet previous astronomical surveys failed to find an obvious population of stars associated with it.
That sounds like strong evidence for a starless galaxy. But astronomers have to be extremely careful.
A cloud containing no bright stars is not automatically a dark galaxy.
Other explanations are possible. For example, the object could be tidal debris pulled from another galaxy, a high-velocity cloud moving through space, or a temporary gaseous structure.
Some of these objects could also contain extremely faint stars that ordinary observations simply cannot detect.
That is why astronomers needed much deeper images.
Looking Deeper Than Ever Before
To investigate Cloud-9, a research team led by Ignacio Trujillo of the Institute of Astrophysics of the Canary Islands used HiPERCAM, a high-speed astronomical camera attached to the Gran Telescopio Canarias (GTC).
The GTC is one of the world's largest optical telescopes.
The researchers observed Cloud-9 during two nights in June 2026. Instead of observing it through just one type of optical filter, they simultaneously collected images through five different filters.
This allowed the researchers to search for extremely faint light that could reveal a hidden population of stars.
But detecting such faint objects is not easy.
The night sky itself produces background light, and even tiny imperfections in image processing can hide or imitate very weak astronomical signals.
The team therefore used a careful observing and processing strategy. Between exposures, they systematically shifted the telescope's pointing position. They also masked the region containing Cloud-9 before estimating and subtracting the background.
This was important because aggressive background subtraction can accidentally remove the very faint, diffuse light astronomers are trying to detect.
The observations ultimately reached a surface-brightness limit of 31.4 magnitudes per square arcsecond in the g-band.
In simple terms, the researchers were able to look extremely deeply for faint and spread-out starlight.
Still No Stars
The result was striking.
Even with these highly sensitive observations, the researchers detected no starlight across Cloud-9's central region.
Instead of simply saying that there are absolutely zero stars, astronomers express the result as an upper limit.
Their observations indicate that the region contains no more than about 16,000 solar masses of stars within an area roughly 4,200 light-years across.
That is an incredibly small stellar population compared with the amount of gas present.
Cloud-9 contains approximately 1 million solar masses of hydrogen gas.
So, even if stars are present, there could be at least 60 times more gas than stars.
For comparison, ordinary galaxies generally have much more obvious stellar populations. Cloud-9 therefore looks remarkably different from the typical galaxy we see in the universe.
Why the Result Matters
The new observations do not prove beyond all doubt that Cloud-9 is a completely starless galaxy.
Instead, they make the case significantly stronger.
The researchers describe Cloud-9 as an excellent candidate for a starless galaxy—a system potentially dominated by gas and dark matter that somehow failed to produce a substantial population of stars.
The result is particularly interesting because it falls between previous estimates.
Earlier survey observations placed limits on how many stars Cloud-9 could contain, but those observations were not specifically designed to preserve extremely faint, low-surface-brightness signals.
Another study using the Hubble Space Telescope attempted to identify individual stars. However, that analysis depended strongly on a comparison galaxy that may have been too compact, potentially affecting the estimate.
The new observations provide an independent test using a different approach.
A Missing Link in Galaxy Formation?
If Cloud-9 is eventually confirmed as a genuinely starless galaxy, it could offer astronomers a rare look at a stage of galaxy formation that is difficult to observe.
The standard cosmological model predicts many small dark matter halos. But astronomers do not yet have a complete picture of how gas behaves inside all of them.
Some halos may successfully form stars and become visible galaxies. Others may remain almost completely dark.
Cloud-9 could represent one of these elusive systems.
Studying it could help scientists understand why some concentrations of dark matter become galaxies filled with stars while others apparently remain almost invisible.
Future observations will be important. Astronomers may look for additional evidence of Cloud-9's structure, motion, gas distribution and possible connection with its surroundings.
For now, Cloud-9 remains a fascinating cosmic mystery: a huge reservoir of hydrogen that appears to have almost nothing shining inside it.
If further observations confirm that it truly contains no meaningful stellar population, Cloud-9 could become an important real-world example of something cosmological models have predicted for decades—a galaxy-like system that formed from dark matter and gas but, for reasons scientists are still trying to understand, never managed to light up with stars.
Reference: Ignacio Trujillo et al, Ultra-Deep imaging of the starless galaxy candidate Cloud-9, arXiv (2026). DOI: 10.48550/arxiv.2608.20911
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