Summary: Astrophysicists have been puzzled by their observations since the 1970s that only a small fraction of matter in the cloud becomes a star and part of a galaxy. They found a lot less of the universe's mass than expected in the middle of galaxies. Things changed when a multi-university collaboration produced a set of new supercomputer models of galaxies called FIRE, The Feedback in Realistic Environments. FIRE simulations ran on the Stampede supercomputer at TACC, an XSEDE resource funded by the National Science Foundation. Theoretical astrophysicist Philip Hopkins of CalTech led a 2014 study of initial results that found that star activity - like supernova explosions or even just starlight - plays a big part in the formation of other stars and the growth of galaxies. Philip Hopkins spoke more about galaxies on FIRE.
