How tiny ‘dead’ galaxies get their groove back and make stars again
Talk about sibling rivalry. Most of the smallest galaxies are “dead,” making no new stars. Now, computer simulations reveal why it is so hard for a tiny galaxy to rejuvenate itself: The galaxy’s existing stars fight the birth of any new ones, even after fresh fuel for star formation falls into the galaxy. These simulations also show that eventually new stars can arise and make the galaxy sparkle again. But it can take many billions of years for a little galaxy to get its star-making mojo back, researchers report April 20 at arXiv.org. Galaxies spawn new stars from gas, but the gas must be cold and dense to collapse into stars. That requirement spelled big trouble for little galaxies soon after the universe’s birth, when ultraviolet radiation from galaxies broke intergalactic hydrogen atoms into protons and electrons (SN: 11/7/19). This process, called reionization, let radiation stream through space and heat gas inside galaxies. The smallest galaxies had so little gas to begin with that it all...