These ‘Ghostly’ Galaxies Have Lost Their Dark Matter

Astronomers studying three faint galaxies, DF2, DF4 and DF9, found that they contain little dark matter, despite dark matter being thought to dominate most galaxies. A study published in June 2026 proposes that the galaxies formed after two ordinary galaxies collided: gas and dust clumped together while dark matter passed through, leaving three galaxies with little dark matter.

The finding supports the idea that dark matter is a physical substance rather than simply a modification of gravity, although its nature remains unknown and it has not been directly detected. DF2 was identified in 2018 and appears to have up to 400 times less dark matter than expected; DF4 was reported in 2019, and DF9 was announced in 2026. DF9 has a mass of about 100 million suns, consistent with its ordinary matter alone; with dark matter, it would be about 100 times more massive.