We present the spectrum of compact object masses: neutron stars and black
holes that originate from single stars in different environments. In
particular, we calculate the dependence of maximum black hole mass on
metallicity and on some specific wind mass loss rates (e.g., Hurley et al. and
Vink et al.). Our calculations show that the highest mass black holes observed
in the Galaxy M_bh = 15 Msun in the high metallicity environment (Z=Zsun=0.02)
can be explained with stellar models and the wind mass loss rates adopted here.
To reach this result we had to set Luminous Blue Variable mass loss rates at
the level of about 0.0001 Msun/yr and to employ metallicity dependent
Wolf-Rayet winds. With such winds, calibrated on Galactic black hole mass
measurements, the maximum black hole mass obtained for moderate metallicity
(Z=0.3 Zsun=0.006) is M_bh,max = 30 Msun. This is a rather striking finding as
the mass of the most massive known stellar black hole is M_bh = 23-34 Msun and,
in fact, it is located in a small star forming galaxy with moderate
metallicity. We find that in the very low (globular cluster-like) metallicity
environment the maximum black hole mass can be as high as M_bh,max = 80 Msun
(Z=0.01 Zsun=0.0002). It is interesting to note that X-ray luminosity from
Eddington limited accretion onto an 80 Msun black hole is of the order of about
10^40 erg/s and is comparable to luminosities of some known ULXs. We emphasize
that our results were obtained for single stars only and that binary
interactions may alter these maximum black hole masses (e.g., accretion from a
close companion). This is strictly a proof-of-principle study which
demonstrates that stellar models can naturally explain even the most massive
known stellar black holes.Comment: 15 pages, ApJ accepte
