NASA/JPL-Caltech
If black holes formed in the first seconds after the big bang, they may still be around in colossal clusters that are practically invisible.
In the very early universe, everything was so dense that the radiation that filled the cosmos could have collapsed to create primordial black holes. If these black holes have survived, they could have become much smaller – and thus harder to detect – than black holes that formed the usual way, through the collapse of a giant star.
Juan García-Bellido at the Autonomous University of Madrid in Spain and his …