Stellar evolution models predict the existence of a gap in the black hole mass spectrum from ∼55 M _⊙–120 M _⊙ due to pair-instability supernovae (PISNe). We investigate the possible existence of such an “upper” mass gap in the second gravitational-wave transient catalog (GWTC-2) by hierarchically modeling the astrophysical distribution of black hole masses. We extend the Truncated and Powerlaw+Peak mass distribution families to allow for an explicit gap in the mass distribution, and apply the extended models to GWTC-2. We find that with the Truncated model there is mild evidence favoring an upper mass gap with log Bayes Factor , inferring the lower and upper bounds at and respectively. When using the Powerlaw+Peak model, we find no preference for the gap. When imposing tighter priors on the gap bounds centered on the expected PISNe gap bounds, the log Bayes factors in favor of a gap mildly increase. These results are however contingent on the parameter inference for the most massive binary, GW190521, for which follow-up analyses showed the source may be an intermediate mass ratio merger that has component masses straddling the gap. Using the GW190521 posterior samples from the analysis in Nitz & Capano (2021), we find an increase in Bayes factors in favor of the gap. However, the overall conclusions are unchanged: there is no preference for a gap when using the Powerlaw+Peak model. This work paves the way for constraining the physics of pair-instability and pulsational pair-instability supernovae and high-mass black hole formation.

恒星演化模型预测，由于对不稳定性超新星 (PISNe)，黑洞质谱中存在 ∼55 M _⊙ –120 M _{⊙ 的}间隙。我们通过对黑洞质量的天体物理分布进行分层建模，研究了在第二个引力波瞬态目录 (GWTC-2) 中可能存在这种“上部”质量间隙。我们扩展了Truncated和Powerlaw+Peak质量分布族，以允许质量分布中存在明显的差距，并将扩展模型应用于 GWTC-2。我们发现使用截断模型，有轻微的证据支持对数贝叶斯因子的质量上限，推断下限和上限为和分别。在使用Powerlaw+Peak模型时，我们没有发现对差距的偏好。当对以预期 PISNe 间隙界限为中心的间隙界限施加更严格的先验时，有利于间隙的对数贝叶斯因子会温和增加。然而，这些结果取决于对最大质量双星 GW190521 的参数推断，后续分析表明其来源可能是一个中等质量比合并，其组分质量跨越了间隙。使用 Nitz & Capano (2021) 分析中的 GW190521 后验样本，我们发现贝叶斯因子的增加有利于差距。但是，总体结论没有变化：使用幂律+峰值时没有偏好间隙模型。这项工作为约束对不稳定性和脉动对不稳定性超新星和大质量黑洞形成的物理学铺平了道路。