Triplet of ‘Ghostly’ Galaxies Hints at What Dark Matter Is — and Isn’t

In 2018, 2019, and 2026, astronomers discovered three faint galaxies named DF2, DF4, and DF9, located about 65 million light-years from Earth.

These galaxies appear dim and diffuse, earning them the nickname 'ghostly galaxies.' Unlike most galaxies, which are held together by dark matter, these three contain almost no dark matter.

For example, DF2 is roughly the size of the Milky Way but has 200 times fewer stars and at most 400 times less dark matter than expected.

This discovery challenged long-held beliefs about how galaxies form and what keeps them stable.