GRS 1915+105: the brightest Galactic black hole

We compare the evolution of spectral shape with luminosity in GRS 1915+105 with that of ‘normal’ black holes. The pathological variability of GRS 1915+105, which probably indicates a disc instability, does not require that GRS 1915+105 belongs in a different class to all the other objects. At comparable fractions of Eddington luminosity its spectra and (more importantly) apparent disc stability are both similar to that seen in the ‘normal’ black holes. Its unique limit-cycle variability only appears when it radiates at uniquely high (super-Eddington) luminosities.