The stars inside a faint galaxy called DF9 drift so slowly that its whole mass matches its visible stars alone. It is the third dark-matter-poor galaxy found strung along one narrow trail in the same patch of sky.
Nearly every galaxy in the universe is wrapped in far more dark matter than starlight. The invisible stuff outweighs the stars by ten or a hundred to one, and in the smallest galaxies its grip is sup… [+7194 chars]