SIMBAD references

Recent measurements of the Kerr parameters of the black holes in M33 X-7 and LMC X-1 yield a_*= 0.84±0.05 and a_*= 0.90^+0.04_–0.09, respectively. We study massive binary evolution scenarios that can reproduce such high values for the Kerr parameters. We first discuss a model with Case C mass transfer leading to a common envelope and tidal synchronization of the primary before it collapses into a black hole. We also study a Case M evolution model (which involves tidally locked, rotationally mixed, chemically homogeneous stars in a close binary). Our analysis suggests that, regardless of the specific scenario, the observed Kerr parameters for the black holes in M33 X-7 and LMC X-1 had to be obtained through hypercritical mass accretion.