The role of thermal instability in accretion outbursts in high-mass stars,Astronomy & Astrophysics

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The role of thermal instability in accretion outbursts in high-mass stars
Astronomy & Astrophysics ( IF 5.4 ) Pub Date : 2024-12-17 , DOI: 10.1051/0004-6361/202451758
Vardan G. Elbakyan, Sergei Nayakshin, Alessio Caratti o Garatti, Rolf Kuiper, Zhen Guo

Context. High-mass young stellar objects (HMYSOs) can exhibit episodic bursts of accretion, accompanied by intense outflows and luminosity variations. Understanding the underlying mechanisms driving these phenomena is crucial for elucidating the early evolution of massive stars and their feedback on star formation processes.Aims. Thermal instability (TI) due to hydrogen ionisation is among the most promising mechanisms of episodic accretion in low-mass (M_{*_{≲ 1 M_{⊙_{) protostars. Its role in HMYSOs has not yet been determined. Here we investigate the properties of TI outbursts in young massive (M_{*_{≳ 5 M_{⊙_{) stars, and compare them to those that have been observed to date.Methods. We employed a 1D numerical model to simulate TI outbursts in HMYSO accretion discs. We varied the key model parameters, such as stellar mass, mass accretion rate onto the disc, and disc viscosity, to assess the TI outburst properties.Results. Our simulations show that modelled TI bursts can replicate the durations and peak accretion rates of long outbursts (a few years to decades) observed in HMYSOs with similar mass characteristics. However, they struggle with short-duration bursts (less than a year) with short rise times (a few weeks or months), suggesting the need for alternative mechanisms. Moreover, while our models match the durations of longer bursts, they fail to reproduce the multiple outbursts seen in some HMYSOs, regardless of model parameters. We also emphasise the significance of not just evaluating model accretion rates and durations, but also performing photometric analysis to thoroughly evaluate the consistency between model predictions and observational data.Conclusions. Our findings suggest that some other plausible mechanisms, such as gravitational instabilities and disc fragmentation, can be responsible for generating the observed outburst phenomena in HMYSOs, and we underscore the need for further investigation into alternative mechanisms driving short outbursts. However, the physics of TI is crucial in sculpting the inner disc physics in the early bright epoch of massive star formation, and comprehensive parameter space exploration; the use of 2D modelling is essential to obtaining a more detailed understanding of the underlying physical processes. By bridging theoretical predictions with observational constraints, this study contributes to advancing our knowledge of HMYSO accretion physics and the early evolution of massive stars.}}}}}}}}

中文翻译：

热不稳定性在大质量恒星吸积爆发中的作用

上下文。大质量年轻恒星天体（HMYSO）可以表现出偶发性的吸积爆发，并伴有强烈的流出和光度变化。了解驱动这些现象的潜在机制对于阐明大质量恒星的早期演化及其对恒星形成过程的反馈至关重要。目标。氢电离引起的热不稳定性（TI）是低质量（M* ≲ 1 M⊙）原星中最有前途的偶发吸积机制之一。它在 HMYSO 中的作用尚未确定。在这里，我们研究了年轻大质量（M* ≳ 5 M⊙）恒星中 TI 爆发的特性，并将它们与迄今为止观察到的进行比较。方法。我们采用 1D 数值模型来模拟 HMYSO 吸积盘中的 TI 爆发。我们改变了关键模型参数，例如恒星质量、盘上的质量吸积率和盘粘度，以评估 TI 爆发特性。结果。我们的模拟表明，建模的 TI 爆发可以复制在具有相似质量特性的 HMYSO 中观察到的长爆发（几年到几十年）的持续时间和峰值吸积率。然而，它们与短持续时间（不到一年）和短上升时间（几周或几个月）作斗争，这表明需要替代机制。此外，虽然我们的模型与较长爆发的持续时间相匹配，但无论模型参数如何，它们都无法再现某些 HMYSO 中出现的多次爆发。我们还强调了不仅要评估模型吸积率和持续时间的重要性，还要进行光度分析以彻底评估模型预测和观测数据之间的一致性。结论。我们的研究结果表明，其他一些合理的机制，例如引力不稳定性和椎间盘碎裂，可能是在 HMYSO 中产生观察到的爆发现象的原因，我们强调需要进一步研究驱动短爆发的替代机制。然而，TI 的物理学对于在大质量恒星形成的早期明亮时代塑造内盘物理学和全面的参数空间探索至关重要;使用 2D 建模对于更详细地了解潜在的物理过程至关重要。通过将理论预测与观测约束联系起来，这项研究有助于推进我们对 HMYSO 吸积物理学和大质量恒星早期演化的了解。