Staring at a small patch of sky for more than 50 hours with
the ultra-sensitive Karl G. Jansky Very Large Array (VLA), astronomers have for
the first time identified discrete sources that account for nearly all the
radio waves coming from distant galaxies. They found that about 63 percent of
the background radio emission comes from galaxies with gorging black holes at
their cores and the remaining 37 percent comes from galaxies that are rapidly
forming stars.