  The component black holes (BHs) observed in gravitational-wave (GW) binary
black hole (BBH) events tend to be more massive and slower spinning than those
observed in black hole X-ray binaries (BH-XRBs). Without modeling their
evolutionary histories, we investigate whether these apparent tensions in the
BH populations can be explained by GW observational selection effects alone. We
find that this is indeed the case for the discrepancy between BH masses in BBHs
and the observed high-mass X-ray binaries (HMXBs), when we account for
statistical uncertainty from the small sample size of just three HMXBs. On the
other hand, the BHs in observed low-mass X-ray binaries (LMXBs) are
significantly lighter than the astrophysical BBH population, but this may just
be due to a correlation between component masses in a binary system. Given
their light stellar companions, we expect light BHs in LMXBs. The observed
spins in HMXBs and LMXBs, however, are in tension with the inferred BBH spin
distribution at the $>99.9\%$ level. We discuss possible scenarios behind the
significantly larger spins in observed BH-XRBs. One possibility is that a small
subpopulation (conservatively $<30\%$) of BBHs have rapidly spinning primary
components, indicating that they may have followed a similar evolutionary
pathway to the observed HMXBs. In LMXBs, it has been suggested that BHs can
spin up by accretion. If LMXB natal spins follow the BBH spin distribution, we
find LMXBs must gain an average dimensionless spin of $0.47^{+0.10}_{-0.11}$,
but if their natal spins follow the observed HMXB spins, the average spinup
must be $<0.03$.
