The Progenitor of GW 150914

The spectacular detection of gravitational waves (GWs) from GW 150914 and its reported association with a gamma-ray burst (GRB) offer new insights into the evolution of massive stars. Here it is shown that no single star of any mass and credible metallicity is likely to produce the observed GW signal. Stars with helium cores in the mass range 35 to 133 solar masses encounter the pair instability and either explode or pulse until the core mass is less than 40 solar masses, smaller than the combined mass of the observed black holes. The rotation of more massive helium cores is either braked by interaction with a slowly rotating hydrogen envelope, if one is present, or by mass loss, if one is not. The very short interval between the GW signal and the observed onset of the putative GRB in GW 150914 is also too short to have come from a single star. A more probable model for making the gravitational radiation is the delayed merger of two black holes made by 70 and 90 solar mass stars in a binary system. The more massive component was a pulsational-pair instability supernova before making the first black hole.