FORMATION AND EVOLUTION OF BINARY NEUTRON-STARS

The formation and evolution of binaries which contain two neutron star s or a neutron star with a black hole companion are discussed in detai l. The evolution of the distributions in orbital period and eccentrici ty for neutron star binaries are studied as a function of time. In the model which fits the observations of high mass binary pulsars best th e deposition of orbital energy into common envelopes has to be very ef ficient and a kick velocity distribution has to contain a significant contribution of low velocity kicks. The estimated age of the populatio n has to be between several 100 Myr and 1 Gyr. The birthrate of neutro n stars binary is similar to 3.4 x 10(-5) yr(-1) (assuming 100% binari ty) and their merger rate is similar to 2 X 10(-5) yr(-1). The merger rate of neutron star binaries is consistent with the estimated rate of gamma-ray bursts, if the latter are beamed into an opening angle of a few degrees. We argue that PSR B2303+46 is possibly formed in a scena rio in which the common envelope is avoided while for the other three known high-mass binary pulsars a common envelope is required to explai n their orbital period.