> Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. No, that's wrong. Narayan, R. and McClintock, J.E.,

> Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. No, that's wrong. Narayan, R. and McClintock, J.E., New Astronomy Reviews, 51, 733–51, 2008 [arxiv: https://arxiv.org/abs/0803.0322 https://arxiv.org/abs/0803.0322 ] has a beautiful chart (Fig. 8) comparing the quiescent bolometric luminosity of star-to-accreting-neutron star binaries and star-to-accreting-black hole binaries. Observed NS binaries are brighter than observed BH (candidate) binaries. This is one test for whether a compact accretor in a binary is a BH rather than an NS. This technique was used by Bennett et al., 2002 and Mao et al., 2002 to find several candidate BHs. - -- Bennett, D.P., Becker, A.C., Quinn, J., et al. (2002). Gravitational microlensing events due to stellar-mass black holes. Astrophysical Journal, 79: 639–59. Mao, S., Smith, M.C., Woz ́niak, P., et al. (2002). Optical Gravitational Lensing Experiment OGLE-1999-BUL-32: the longest ever microlensing event—evidence for a stellar mass black hole? Monthly Notices of the Royal Astronomical Society, 329: 349–54.