SIMBAD references

We work out the effects of hypercritical accretion, which transfers mass from the secondary to the primary (older) neutron star (NS) in a binary, showing that such accretion would cause the mass of the primary to end up ≳0.6 M_☉ greater than the secondary NS, in contradiction with the very nearly equal masses measured in binary neutron stars to date. We point out that the primary NS will evolve into a low-mass black hole (LMBH) as a consequence of hypercritical accretion. Using a flat distribution in the mass ratio q (≡M_secondary/M_primary), favored by Duquennoy & Mayor, we calculate the ratio of LMBH-NS to NS-NS systems to be ∼5, in rough agreement with the result of Pinsonneault & Stanek. The latter authors emphasized the importance of ``twins'', which we discuss. The two neutron stars in twin systems would be close in mass and further increase the number of mergers.