GRS 1915+105

Abstract

I summarize recent near-infrared spectroscopy of the microquasar GRS 1915+105 with the ESO/VLT which allowed to (i) identify the donor and (ii) measure the orbital period and radial velocity amplitude. Assuming that the jet ejections occur perpendicular to the accretion disk and orbital plane, the mass of the black hole is determined to M = 14 +- 4 solar masses. I discuss the implications of this mass determination on (a) the understanding of the large-amplitude X-ray variability in GRS 1915+105, (b) binary formation scenarios, and (c) models to explain the stable QPO frequencies in GRS 1915+105 and GRO J1655-40.