Formation of GW190521 from stellar evolution: the impact of the hydrogen-rich envelope, dredge-up, and 12C(α, γ)16O rate on the pair-instability black hole mass gap
Formation of GW190521 from stellar evolution: the impact of the hydrogen-rich envelope, dredge-up, and 12C(α, γ)16O rate on the pair-instability black hole mass gap
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DOI：
10.1093/mnras/staa3916
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发表时间：
2020-10
影响因子：
4.8
通讯作者：
G. Costa;A. Bressan;M. Mapelli;P. Marigo;G. Iorio;M. Spera
中科院分区：
文献类型：
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作者：
G. Costa;A. Bressan;M. Mapelli;P. Marigo;G. Iorio;M. Spera
对不稳定性（PI）有望在黑洞（BHs）的质谱中打开一个≈40-65和≈120 M⊙之间的缺口。GW190521的发现正在挑战质量间隙的存在，其主要成分质量为$85^{+21}_{-14}$ M⊙。在这里，我们研究了PI质量间隙的主要不确定因素：12C(α, γ)16O反应速率和富h包膜坍缩。在标准的12C(α, γ)16O速率下，如果考虑金属丰度Z≤0.0003时残余富h包层的坍缩，则质量间隙下缘可达70 M⊙。采用starlib数据库给出的不确定性，用12C(α, γ)16O率$-1\,\sigma$计算模型，我们发现π质量间隙在≈80 ~≈150 M⊙之间。具有MZAMS > 110 M⊙的恒星可能会在核心氦燃烧阶段经历一个深度挖掘阶段，从核心中提取物质以丰富外壳。由于氦核质量的减少，MZAMS = 160 M⊙的恒星可能会避开π并产生150 M⊙的黑洞。在$-2\,{}\sigma{}$的情况下，π的质量间隙在92 ~ 110 M⊙之间。最后，在用12C(α, γ)16O $-3\, {}\sigma{}$计算的模型中，质量间隙被疏通效应完全消除。这种疏浚的开始对假定的对流和混合模式特别敏感。富h包络坍缩和低12C(α, γ)16O速率的共同作用可导致形成质量与GW190521主成分一致的黑洞。
Pair-instability (PI) is expected to open a gap in the mass spectrum of black holes (BHs) between ≈40–65 and ≈120 M⊙. The existence of the mass gap is currently being challenged by the detection of GW190521, with a primary component mass of $85^{+21}_{-14}$ M⊙. Here, we investigate the main uncertainties on the PI mass gap: the 12C(α, γ)16O reaction rate and the H-rich envelope collapse. With the standard 12C(α, γ)16O rate, the lower edge of the mass gap can be 70 M⊙ if we allow for the collapse of the residual H-rich envelope at metallicity Z ≤ 0.0003. Adopting the uncertainties given by the starlib database, for models computed with the 12C(α, γ)16O rate $-1\, \sigma$, we find that the PI mass gap ranges between ≈80 and ≈150 M⊙. Stars with MZAMS > 110 M⊙ may experience a deep dredge-up episode during the core helium-burning phase, that extracts matter from the core enriching the envelope. As a consequence of the He-core mass reduction, a star with MZAMS = 160 M⊙ may avoid the PI and produce a BH of 150 M⊙. In the $-2\, {}\sigma {}$ case, the PI mass gap ranges from 92 to 110 M⊙. Finally, in models computed with 12C(α, γ)16O $-3\, {}\sigma {}$, the mass gap is completely removed by the dredge-up effect. The onset of this dredge-up is particularly sensitive to the assumed model for convection and mixing. The combined effect of H-rich envelope collapse and low 12C(α, γ)16O rate can lead to the formation of BHs with masses consistent with the primary component of GW190521.