If you take a galaxy and try to make it bigger, it becomes a cluster of galaxies, not a galaxy. If you try to make it smaller than that, it seems to blow itself apart.
Jeremiah P. OstrikerThere are reasons, increasing in number and quality, to believe that the masses of ordinary galaxies may have been underestimated by a factor of 10 or more.
Jeremiah P. OstrikerBiology has tended to be an observational science and deriving things from first principles has not been possible in the past but I hate to predict the future on that.
Jeremiah P. Ostriker