Formation and evolution of microquasar GRS 1915+105

Using the StarTrack population synthesis code, we analyze the possible formation channels of the Galactic microquasar GRS 1915+105, harboring the most massive known stellar black hole. We find that the evolution and the current state of GRS 1915+105 can be reproduced in a model with lowered wind mass-loss rates in massive stars. We conclude that the existence of GRS 1915+105 implies that stellar winds in massive stars are a factor of 2 weaker-but still within observational bounds-than those used in stellar models. We discuss the mass transfer initiated by the massive primary in binaries, which are the possible precursors of systems harboring massive black holes, and show that it is not clearly either case B or C but is instead initiated during the core helium-burning phase of the massive donor star, the progenitor of the black hole. We also argue that massive black holes do not receive any kicks at their formation and are formed through direct collapse of the progenitor star without an accompanying supernova explosion.