Astronomers have discovered a rare kind of galaxy that seems to be missing one of the universe’s most important ingredients: dark matter.
Using powerful telescopes in Hawaiʻi and data from the Hubble Space Telescope, researchers found that a faint, distant galaxy called FCC 224 appears to have little or no dark matter—something that’s usually considered essential for forming and holding galaxies together.
FCC 224 is an ultra-diffuse dwarf galaxy located on the edge of the Fornax Cluster, about 60 to 65 million light-years away from Earth.
What makes it so unusual is that it contains an unexpectedly large number of bright star clusters—but barely any dark matter, at least in its inner regions.
This surprising find is now making scientists rethink how galaxies like this form.
Dark matter is an invisible substance that doesn’t emit light or energy, but it makes up most of the universe’s mass.
Astronomers believe it acts like a cosmic glue, helping galaxies stay together. According to the standard model of cosmology, galaxies simply shouldn’t exist without it.
But FCC 224 seems to break those rules.
The discovery is detailed in two recent studies. One, led by Yimeng Tang at the University of California, Santa Cruz, focused on the galaxy’s star clusters using images from the Hubble Space Telescope.
The other study, led by Maria Luísa Buzzo from Swinburne University and the European Southern Observatory, used the Keck Observatory’s advanced Keck Cosmic Web Imager (KCWI) to closely examine how stars move within FCC 224.
Both researchers found the galaxy has a very low “velocity dispersion”—meaning its stars and star clusters move much more slowly than expected. This slow movement is a strong clue that there’s not much dark matter pulling on them.
Buzzo and Tang compared FCC 224 to two other known dark matter-deficient galaxies, called DF2 and DF4, found in a different part of the sky. FCC 224 shares some of their characteristics, suggesting it may be part of a new class of galaxies that lack dark matter entirely or have lost most of it.
How did this happen? One idea is that FCC 224 experienced a high-speed collision in the past that stripped away its dark matter while leaving behind the visible parts—a scenario called the “bullet-dwarf model.” But more observations are needed to test this theory.
The discovery suggests that galaxies without dark matter might be more common than scientists once thought. If more of these galaxies are found, they could change our understanding of how galaxies form and what role dark matter really plays in the universe.
