Merging of binary white dwarfs, neutron stars and black holes under the influence of gravitational wave radiation

By means of a numerical scenario code, we derive the rates of mergers of components of binary white dwarfs, neutron stars and black holes as functions of the ages of the progenitor populations. The rate of mergers of binary CO (or ONe) dwarfs with total mass of components ≳ M_Ch is consistent with the ‘observed’ rate of occurrence of Type Ia supernovae (SNeIa) in the Galaxy. We show that, for galaxies with continuing intense star formation, the history of star formation is not significant for the present rate of SNeIa, because about 60 per cent of SNeIa descend from populations younger than ∼10⁹ yr. Assuming that Type Ib and Type II supernovae (SNeIb and SNeII) descend, respectively, from compact helium remnants of initially massive ($$M\gtrsim10\rm{M}_\odot$$) components of close binaries and from massive stars that managed to retain their extended hydrogen envelopes, we estimate their rates and derive linear relations between the rates of occurrence of SNeIa, SNeIb and SNeII that have the same trend along the portion of the Hubble sequence for non-elliptical galaxies as indicated by observations. We compute the average distances that merging pairs with neutron star and/or black hole components can travel prior to mergers, and find that the overwhelming majority of merger events have to occur within the volume of the parental galaxies.