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Three galaxies located about 65 million light-years from Earth appear dim and lack the usual swirl of stars. Astrophysicist Michael Keim describes them as having a "ghostly appearance." These objects, known as DF2, DF4, and DF9, are unusual because they contain very little dark matter. Dark matter is an invisible substance that acts as cosmic glue, holding galaxies together by pulling ordinary matter inward. Without it, stars would fly apart due to their own gravity.

A paper published in June 2026 suggests these galaxies formed after a collision between two regular galaxies. In such an event, the dark matter passed through each other like ghosts because it interacts only with gravity. The ordinary matter, however, clumped together to form new stars. This process left behind three galaxies that are nearly devoid of dark matter. While some scientists have proposed that gravity itself might be different rather than dark matter existing, these findings suggest dark matter is a physical substance.

The existence of DF2, discovered in 2018, and its companion DF4, observed in 2019, challenged astronomers. DF2 has roughly the same size as the Milky Way but contains only about 200 times fewer stars. Measurements showed it had at most 400 times less dark matter than expected. A third galaxy, DF9, announced in 2026, has a mass consistent with ordinary matter alone; if it contained typical dark matter, it would be 100 times more massive. Experts note that while the exact origin story is debated, the lack of dark matter strongly supports its physical reality over modified gravity theories like MOND.