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

Astronomers have discovered three diffuse galaxies (DF2, DF4, and DF9) that contain very little dark matter, challenging existing theories about its nature. A proposed explanation suggests these galaxies formed from a collision of two regular galaxies, where ordinary matter clumped together while dark matter passed through, leaving behind dark matter-deficient remnants. This finding provides crucial insights into the properties of dark matter.