To date, at least 19 galaxies have been discovered that appear to be missing dark matter altogether. What this means, in practice, is that these galaxies are rotating so slowly that no additional matter, beyond their complement of visible baryons, is required to explain their gravitational coherence. Only fast-spinning galaxies need the gravitational attraction of extra matter to hold them together; our traditional understanding of gravity is enough to keep the slow-spinning ones from flying apart.
