Sensitivity of the lower edge of the pair-instability black hole mass gap to the treatment of time-dependent convection

Abstract

Gravitational-wave detections are now probing the black hole (BH) mass distribution, including the predicted pair-instability 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 turn-over timescale. This invalidates the steady-state assumption on which the classic mixinglength theory relies. We compare the final BH masses computed with two different versions of the stellar evolutionary code 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 M . The differences are much smaller for the progenitors which determine the maximum mass of BHs below the gap. This prediction is robust at M BH,max 48 M , at least within the idealized context of this study. This is an encouraging indication that current models are robust enough for comparison with the present-day 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 gravitational wave detectors.

Constraints from Gravitational-wave Detections of Binary Black Hole Mergers on the 12C(α, γ)16O Rate

“…This turnover may be detectable in the inferred black hole mass distribution (see model C of Abbott et al 2019b). There may also be a small bump in the black hole mass distribution at the interface between the stars undergoing CC and the lightest PPISN progenitors, depending on the strength of the mass loss in the latter (Renzo et al 2020b). We chose not to show Figure 8 in terms of the carbon core mass, which is the more applicable quantity to show when comparing between different metallicities (Farmer et al 2019), because the highest s C12 models have » X C 0 12 ( ) in their cores.…”

“…As the initial mass increases, and the pulses get stronger and thus remove more mass, they can ( ) , and may provide constraints in a reduced temperature region (that associated with helium shell burning, < < T 0.3 GK 1.0 / ). Further work is needed to quantify the amount of mixing in the outer layers of the star (Renzo et al 2020b), to understand which parts of the ejecta (and thus which layers of the star) would be measured in spectroscopy of a PPISN (Renzo et al 2020a), and to investigate the effect of a larger nuclear network in order to follow in greater detail the nucleosynthetic yields from the explosive oxygen burning West et al 2013).…”

Properties and Astrophysical Implications of the 150 M⊙ Binary Black Hole Merger GW190521

“…In addition to this, there are critical uncertainties on other physical ingredients that combine with PI and PPI to shape the mass spectrum of BHs (e.g., Belczynski et al 2016Belczynski et al , 2020Stevenson et al 2019). Recently, Farmer et al (2019) and Renzo et al (2020) have investigated the main sources of uncertainty on the lower edge of the PI mass gap, by modeling naked helium cores. The impact of time-dependent convection on the location of the lower edge of the PI mass gap is found to be Δm≈5 M e (Renzo et al 2020).…”

“…Recently, Farmer et al (2019) and Renzo et al (2020) have investigated the main sources of uncertainty on the lower edge of the PI mass gap, by modeling naked helium cores. The impact of time-dependent convection on the location of the lower edge of the PI mass gap is found to be Δm≈5 M e (Renzo et al 2020). Variations in the treatment of convective mixing and neutrino physics are found to have small effects on the maximum BH mass (with a mass variation Δm≈1-2 M e ), while different stellar metallicity and wind mass-loss prescriptions have more conspicuous repercussions (Δm≈4 M e ).…”

The impact of stellar rotation on the black hole mass-gap from pair-instability supernovae

“…Currently, significant work is conducted to study what can modify the predicted location of this mass gap, including uncertainties in nuclear reaction rates (Takahashi 2018;Farmer et al 2019), convection (Renzo et al 2020), the presence of a massive hydrogen envelope at iron-core collapse (Di Carlo et al 2019), and accretion after BH formation (van Son et al 2020). Regarding rotation, work has been done to study how it affects the evolution of a star prior to a PPISN or PISN (Chatzopoulos et al 2013;Mapelli et al 2020), but there is still a large uncertainty on how rotation affects the actual hydrodynamics of these events.…”