All Apples: Comparing black holes in X-ray binaries and gravitational-wave sources.

Black hole components in LIGO/Virgo mergers are more massive than black holes observed in X-ray binaries. Black--hole spins deduced from model--dependent fits to X-ray binary observations give larger values than those deduced for LIGO/Virgo black holes. These two statements have been used to conclude that LIGO/Virgo black holes and X-ray binary black holes form two distinct populations (apples and oranges). Here we show why this conclusion is not secure.