Most likely explanation for ULXs?
a 30-50 Msun BH
accreting from an O star
via Roche-lobe overflow
ß NS or BH
accreting from a low-mass star via
Roche-lobe overflow (LMXB)
ß NS or BH
accreting from a high-mass star via
stellar wind (HMXB)
ß NS or BH
accreting from a high-mass star via
Roche-lobe overflow (ULX + LMC X-4)
Three classes of X-ray binaries?