Maximum PBH Mass and Primordiality
  In order to avoid unacceptable $\mu$-distortions inconsistent with
observational data on the Cosmic Microwave Background, Primordial Black Holes
(PBHs) must be less massive than $10^{12} M_{\odot}$, quite closely above the
highest black hole mass yet observed. This comparableness leads us to posit
that all supermassive black holes originate as PBHs.
