The Intrinsic Magnetic Fields of the Galactic Black Hole Candidates
  Recent work has linked the quiescent luminosities and hard/soft spectral state switches of neutron stars (NSs) to their spinning magnetic fields. It is shown here that the quiescent luminosities and spectral switches of galactic black hole candidates (BHCs) could be produced in the same way for spin rates below 100 Hz and magnetic fields above 10^10 G. It is also shown that the ultrasoft peaks and large flickering amplitudes of the BHCs would be expected from the surfaces of massive NSs. None of the few spectral characteristics that distinguish BHCs from low mass NSs have been explained in terms of event horizons. Serious consideration of the possibility that they might simply be massive NSs opens an avenue for proof of event horizons by negation, but requires the use of a space-time metric that has no event horizon. The Yilmaz exponential metric used here is shown to have an innermost marginally stable orbit with radius, binding energy and Keplerian frequency that are within a few percent of the same quantities for the Schwarzschild metric. A maximum NS mass of ~10 solar mass is found for the Yilmaz metric. The two metrics essentially differ only by the presence/absence of a surface for the BHCs, thus enabling proof or disproof of the existence of an event horizon. 
Stanley L. Robertson (Southwestern Oklahoma State University)