The mass function for black holes at birth in close binary systems is explored .
The effects of varying the mass-loss rate and metallicity are calculated using a simple semi-analytic approach to stellar evolution that is tuned to reproduce detailed numerical calculations .
Though the total fraction of black holes made in stellar collapse events varies considerably with metallicity , mass-loss rate , and mass cutoff , from 5 % to 30 % , the shapes of their birth functions are very similar for all reasonable variations in these quantities .
Median neutron star masses are in the range 1.32 – 1.37 \mathrm { M } _ { \odot } regardless of metallicity .
The median black hole mass for solar metallicity is typically 8 to 9 \mathrm { M } _ { \odot } if only initial helium cores below 40 \mathrm { M } _ { \odot } ( ZAMS mass less than 80 \mathrm { M } _ { \odot } ) contribute , and 9 – 13 \mathrm { M } _ { \odot } , in most cases , if helium cores up to 150 \mathrm { M } _ { \odot } ( ZAMS mass less than 300 \mathrm { M } _ { \odot } ) contribute .
As long as the mass-loss rate as a function of mass exhibits no strong non–linearities , the black hole birth function from 15 to 35 \mathrm { M } _ { \odot } has a slope that depends mostly on the initial mass function for main sequence stars .
These findings imply the possibility of constraining the initial mass function and the properties of mass loss in close binaries using ongoing measurements of gravitational wave radiation .
The expected rotation rates of the black holes are discussed .