ON THE NATURE OF THE BINARY RADIO PULSAR PSR-B0042-73 IN THE SMALL MAGELLANIC CLOUD

The modern scenario of evolution of massive binary systems predicts th e existence of a subclass of binary radio pulsars (PSRs) with black ho les (BHs). Their Galactic number was evaluated as similar to 1 per 100 0 single pulsars (Lipunov et al. 1994b). Distinctive properties of suc h binaries would be (1) mass of the unseen companion M(c) > 3-4 M(circ le dot) and (2) absence of eclipses of the pulsar radiation with no di stinctive variance of the dispersion measure along the pulsar orbit. T he pulsars themselves must be similar to standard isolated ones. The r ecently discovered binary 1 s pulsar PSR B0042-73 = PSR J0045-7319 in the Small Magellanic Cloud (SMC) with a massive companion in a highly elongated (eccentricity e = 0.8) 51 day orbit (Kaspi et al. 1994) may be the first such pulsar with a BH. The paradoxical fact that the firs t pulsar discovered in the SMC proved to be in a binary system can be naturally understood if its companion actually is a 10-30 M(circle dot ) black hole. We illustrate this fact by the numerical calculation of evolution of radio pulsars after a star formation burst.