Astronomers find another galaxy that appears to lack dark matter

A rare galaxy without dark matter may strengthen an unusual cosmic case

Astronomers have identified what appears to be another galaxy with little or no dark matter, adding a new data point to one of the stranger puzzles in modern astrophysics. The object, a dwarf galaxy known as DF9, sits within a string of a dozen small galaxies in the NGC 1052 field and is now being discussed alongside DF2 and DF4, two other galaxies in the same grouping that have also been reported as lacking dark matter.

If the interpretation holds, the finding is notable not only because such galaxies are rare, but because it suggests the three objects may share a common origin in an extreme event. Researchers say that event may have violently separated ordinary matter from dark matter, leaving behind diffuse, ghostly galaxies that do not resemble the standard picture of galactic formation.

The work was described in a study published June 16 in The Astrophysical Journal and highlighted this week after researchers characterized DF9 as the third known galaxy in the string to appear dark-matter deficient.

Why dark matter matters so much

Dark matter is central to current models of how galaxies form and behave. Although it cannot be seen directly, astronomers infer its presence from gravitational effects, including the motion of stars around galactic centers. The source material notes that dark matter makes up about 85% of the matter in the cosmos and is often described as the gravitational framework, or “cosmic glue,” around which galaxies assemble.

That is why a galaxy apparently missing this invisible mass is so consequential. In the standard view, dark matter halos help gather the gas and material that eventually form stars and galaxies. A system that exists with little dark matter challenges assumptions about what conditions are necessary for a galaxy to take shape and survive.

The interest here is amplified by repetition. One unusual galaxy might be dismissed as a measurement problem or a highly atypical outlier. But a string containing multiple diffuse dwarf galaxies, three of which appear to lack dark matter, is harder to ignore. It raises the possibility that the group records a distinct physical process rather than a one-off anomaly.

The DF9 result and the “string” of dwarf galaxies

DF9 lies in a long trail of faint dwarf galaxies in the NGC 1052 field. Researchers studied the object using the Keck Cosmic Web Imager at the W. M. Keck Observatory on Mauna Kea in Hawaii. According to the report, the larger pattern is one of the most surprising features of the discovery: DF2, DF4, and DF9 may all have formed together in the aftermath of an extreme event, producing galaxies with bright star clusters, a diffuse appearance, and an apparent lack of dark matter.

Michael Keim, the first author of the study and an astrophysicist at Yale’s Graduate School of Arts and Sciences, said the finding suggests an entire trail of galaxies formed together in conditions unlike those seen before. That framing is important because it shifts the conversation away from isolated oddities and toward a broader physical mechanism.

The galaxies are described as small and ghostly, an image that fits the tension at the heart of the result. They are visible enough to study, yet seem to be missing the dominant matter component that should normally underpin their structure. That contradiction is exactly what makes them scientifically useful.

A collision-based explanation is gaining support

The leading interpretation cited in the source text is that violent galactic collisions can strip dark matter away from visible matter. In that scenario, an energetic interaction could create a trail of unusual dwarf galaxies from material displaced during the collision, leaving some descendants with far less dark matter than expected.

This is not the same as proving dark matter does not exist. In fact, the argument depends on dark matter being real and normally abundant. The significance is more specific: under certain extreme conditions, the relationship between visible matter and dark matter may be disrupted strongly enough to produce galaxies that look radically different from the norm.

That possibility matters because astrophysics often advances through edge cases. Objects that sit outside standard expectations can expose hidden assumptions in theory, reveal overlooked processes, or force improvements in measurement. DF9 may prove valuable for all three reasons. It provides a fresh test of whether dark-matter-poor galaxies can be created dynamically, and whether groups of them can preserve the imprint of a shared event over time.

What astronomers will need to resolve next

Even with the attention the finding is receiving, the result remains part of an active scientific discussion rather than a settled rewrite of cosmology. The immediate challenge is to strengthen the observational case around DF9 itself and the broader chain of dwarf galaxies. Researchers will want to refine mass estimates, compare stellar motions more closely, and test whether the three galaxies truly fit one formation history.

Another key question is how unique this system really is. If more strings of dwarf galaxies with similar properties are found elsewhere, the case for collision-driven dark-matter separation would grow stronger. If not, the NGC 1052 field may remain a rare but still highly informative exception.

For now, the importance of DF9 lies in how it reinforces a pattern already considered extraordinary. Dark matter remains the dominant framework for explaining galaxy behavior on large scales. But findings like this suggest the universe may contain more pathways to making galaxies than the cleanest textbook model implies.

That is the deeper scientific value of the discovery. Whether DF9 ultimately confirms a collision-based explanation or prompts a revised interpretation, it is forcing closer scrutiny of how galaxies inherit, lose, or redistribute the matter that shapes them. In a field where invisible mass does much of the heavy lifting, a galaxy that appears to be missing it is bound to attract attention.

This article is based on reporting by Live Science. Read the original article.