The Birth Function for Black Holes and Neutron Stars in Close Binaries
Abstract
The mass function for black holes and neutron stars at birth is explored for mass-losing helium stars. These should resemble, more closely than similar studies of single hydrogen-rich stars, the results of evolution in close binary systems. 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 ${M}_{\odot }$ regardless of metallicity. The median black hole mass for solar metallicity is typically 8-9 ${M}_{\odot }$ if only initial helium cores below 40 ${M}_{\odot }$ (ZAMS mass less than 80 ${M}_{\odot }$ ) are counted, and 9-13 ${M}_{\odot }$, in most cases, if helium cores with initial masses up to 150 ${M}_{\odot }$ (ZAMS mass less than 300 ${M}_{\odot }$ ) contribute. As long as the mass-loss rate as a function of mass exhibits no strong nonlinearities, the black hole birth function from 15 to 35 ${M}_{\odot }$ 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 briefly discussed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2020
- DOI:
- 10.3847/1538-4357/ab8cc1
- arXiv:
- arXiv:2001.10492
- Bibcode:
- 2020ApJ...896...56W
- Keywords:
-
- Stellar mass black holes;
- Core-collapse supernovae;
- Neutron stars;
- Stellar mass loss;
- Close binary stars;
- Stellar evolutionary models;
- Massive stars;
- 1611;
- 304;
- 1108;
- 1613;
- 254;
- 2046;
- 732;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- submitted to ApJ