Dynamically Established BH Systems
Optical and infrared measurements can be used to estimate the mass of candidate black holes. Such observations constitute the strongest evidence for the existence of stellar-mass black holes in binary systems. Currently there are at least 10 systems for which dynamical mass determinates result in the compact object having mass greater than 3 M0, the theoretical upper limit of a neutron star. Hard X-ray surveys can constrain the number of black hole X-ray binaries, which may be in excess of 1000.
Zhang et al. 1997, Proc. 4th Compton Symp., AIP Conf Proc. 410, p. 141.