The impact of masstransfer physics on the observable properties of field binary black hole populations
Abstract
We study the impact of masstransfer physics on the observable properties of binary black hole populations that formed through isolated binary evolution. We used the POSYDON framework to combine detailed MESA binary simulations with the COSMIC population synthesis tool to obtain an accurate estimate of merging binary black hole observables with a specific focus on the spins of the black holes. We investigate the impact of massaccretion efficiency onto compact objects and commonenvelope efficiency on the observed distributions of the effective inspiral spin parameter χ_{eff}, chirp mass M_{chirp}, and binary mass ratio q. We find that low common envelope efficiency translates to tighter orbits following the common envelope and therefore more tidally spun up secondborn black holes. However, these systems have short merger timescales and are only marginally detectable by current gravitationalwave detectors as they form and merge at high redshifts (z ∼ 2), outside current detector horizons. Assuming Eddingtonlimited accretion efficiency and that the firstborn black hole is formed with a negligible spin, we find that all nonzero χ_{eff} systems in the detectable population can come only from the common envelope channel as the stable masstransfer channel cannot shrink the orbits enough for efficient tidal spinup to take place. We find that the local rate density (z ≃ 0.01) for the common envelope channel is in the range of ∼17113 Gpc^{‒3} yr^{‒1}, considering a range of α_{CE} ∈ [0.2, 5.0], while for the stable mass transfer channel the rate density is ∼25 Gpc^{‒3} yr^{‒1}. The latter drops by two orders of magnitude if the mass accretion onto the black hole is not Eddington limited because conservative mass transfer does not shrink the orbit as efficiently as nonconservative mass transfer does. Finally, using GWTC2 events, we constrained the lower bound of branching fraction from other formation channels in the detected population to be ∼0.2. Assuming all remaining events to be formed through either stable mass transfer or common envelope channels, we find moderate to strong evidence in favour of models with inefficient common envelopes.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 March 2021
 DOI:
 10.1051/00046361/202039804
 arXiv:
 arXiv:2010.16333
 Bibcode:
 2021A&A...647A.153B
 Keywords:

 black hole physics;
 gravitational waves;
 stars: black holes;
 binaries : close;
 stars: massive;
 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology
 EPrint:
 26 pages, 13 figures, accepted for publication in A&