Yimeng Tang

Galaxies without dark matter are like beads from which the invisible thread has been ripped. Stretching around the elliptical NGC 1052 is a chain of eight ghostly dim dwarfs: they contain almost none of the mysterious mass that makes spiral arms rotate. Vera Rubin first showed that without the invisible framework, stars would fly apart.

Faint galaxies scattered across the Perseus cluster are like ghosts among their bright neighbors. They are so diffuse that distant objects shine through them, and they contain hundreds of times fewer stars than our Milky Way.