So far, there's been a general rule for galaxies that the ratio of dark-matter calculated from the movements of the galaxy's stars and the estimated mass of all the visible stars in the galaxy varies in a generally predictable way depending on the visible mass of the galaxy.
Well, the new development is that astronomers have found a class of very low mass highly diffuse galaxies that don't obey the rule and whose motions suggest that the amount of dark matter present is at least 400 X lower than predicted and consistent with zero.
https://www.nature.com/articles/nature25767
Hypothetical invisible stuff can't be seen! Scientists amazed! (Sorry, couldn't resist that.)
Well, the new development is that astronomers have found a class of very low mass highly diffuse galaxies that don't obey the rule and whose motions suggest that the amount of dark matter present is at least 400 X lower than predicted and consistent with zero.
https://www.nature.com/articles/nature25767
Hypothetical invisible stuff can't be seen! Scientists amazed! (Sorry, couldn't resist that.)