Why is massive star formation quenched in galaxy centers?
(PHYSorg.com Space & Earth)

The current cosmological model to explain the universe, the `Big Bang` model, aims to describe all observable phenomena, including the evolution of galaxies from earliest times to the present day. One of the major problems in the Standard Model is that it predicts a star formation rate that is far too high. All the star-forming material in galaxies should have coalesced into stars when the universe was only a fraction of its present age of 13.8 billion years. However, over half the galaxies we see, mainly spirals, are actively forming stars right now. This discrepancy between theoretical prediction and observation has forced researchers to look much more closely at star formation quenching processes that can slow down the rate of star formation over the lifetimes of galaxies. Without this quenching, the standard Big Bang model fails to predict the universe as we know it.