Bayesian analysis of the spin distribution of LIGO/Virgo black holes
  Gravitational wave detection from binary black hole (BBH) inspirals has
become routine thanks to the LIGO/Virgo interferometers. The nature of these
back holes remains uncertain. We study here the spin distributions of
LIGO/Virgo black holes from the first catalogue GWTC-1 and the first four
published BBH events from run O3. We compute the Bayes evidence for several
independent priors: flat, isotropic, spin-aligned and anti-aligned. We find
strong evidence for low spins in all of the cases, and significant evidence for
small isotropic spins versus any other distribution. When considered as a
homogeneous population of black holes, these results give support to the idea
that LIGO/Virgo BBH are primordial.
