Sensitivity of the lower edge of the pairinstability black hole mass gap to the treatment of timedependent convection
Abstract
Gravitationalwave detections are now probing the black hole (BH) mass distribution, including the predicted pairinstability mass gap. These data require robust quantitative predictions, which are challenging to obtain. The most massive BH progenitors experience episodic mass ejections on timescales shorter than the convective turnover timescale. This invalidates the steadystate assumption on which the classic mixing length theory relies. We compare the final BH masses computed with two different versions of the stellar evolutionary code $\tt{MESA}$ : (i) using the default implementation of Paxton et al. (2018) and (ii) solving an additional equation accounting for the timescale for convective deceleration. In the second grid, where stronger convection develops during the pulses and carries part of the energy, we find weaker pulses. This leads to lower amounts of mass being ejected and thus higher final BH masses of up to ∼ $5\, \mathrm{M}_\odot$ . The differences are much smaller for the progenitors that determine the maximum mass of BHs below the gap. This prediction is robust at $M_{\rm BH, max}\simeq 48\, \mathrm{M}_\odot$ , at least within the idealized context of this study. This is an encouraging indication that current models are robust enough for comparison with the presentday gravitationalwave detections. However, the large differences between individual models emphasize the importance of improving the treatment of convection in stellar models, especially in the light of the data anticipated from the third generation of gravitationalwave detectors.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2020
 DOI:
 10.1093/mnras/staa549
 arXiv:
 arXiv:2002.08200
 Bibcode:
 2020MNRAS.493.4333R
 Keywords:

 convection;
 methods: numerical;
 stars: black holes;
 stars: massive;
 Astrophysics  Solar and Stellar Astrophysics;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 7 pages + 1 appendix, accepted in MNRAS, online results at https://zenodo.org/record/3406320