Were vast numbers of black holes spawned during our universe’s earliest moments?

So far, there is no hard evidence that such primordial black holes (PBHs) ever existed, but new observations just around the corner could change that. The black holes emit X-rays that can escape the vicinity of the black holes to ionize hydrogen atoms. This would subtly affect how matter distributes itself into regions of high and low density — a distribution reflected in the cosmic microwave background radiation.