Cosmic Impact of Massive Stars: Convective Mixing and Mass Loss

该联盟提案的目的是改进宇宙中最大质量恒星的数值计算。大质量恒星通过它们发出的光线和产生的化学元素发挥着关键作用。在它们生命的末期，它们的核心会坍塌成黑洞，因为它们的引力是如此巨大，甚至连光都无法逃脱。大质量恒星的生命和相关化学与几个关键的STFC路线图问题有关。“问题A：宇宙是如何开始的，它是如何演化的？”：恒星可以用来探测宇宙及其从婴儿期开始的演化，事实上，第一批恒星是在大爆炸后4亿年才形成的。即使这些恒星中的大多数早已死亡，它们的化学指纹也储存在寿命长、质量极低、金属含量极低的恒星中，这些恒星如今还存活着。将我们的模型与对这些贫金属星的观测进行比较，可以提供有关第一批恒星和星系的性质的信息(问题A4)，更广泛地说，这项提议解决了关键问题A5和A6：“星系和恒星是如何演化的？”恒星模型也被用作解释大型观测调查的理论框架，例如VLT-Flames对大质量恒星的调查，以及研究迄今尚未解释的观测。例如，我们的模型衡量了迄今为止发现的最大质量的恒星，而确定的质量(出生时高达320个太阳质量)极大地颠覆了以前恒星的质量上限。此外，我们的恒星模型将是超新星模拟的主要输入。因此，该项目还解决了这样一个问题：“D：我们如何探索和理解宇宙的极端？”恒星模型还通过约束发射“重”黑洞的引力波的质量，为最近打开的引力波窗口(`‘D2：引力波特性’)提供了输入。质量损失是决定大质量恒星最终质量的关键过程，因为它们通过强大的恒星风失去了超过一半的初始成分。恒星模型为解释来自实验和观测设施的数据提供了一个关键的理论框架，这些设施代表着数十亿英镑的投资。然而，理论在观测/实验方面落后于进展，限制了科学进步。在我们的提案中开发的恒星模型将为解释STFC资助的设施提供迫切需要的改进的理论框架，将利用STFC的计算设施，并将它们连接到STFC支持的核物理设施。因此，我们的工作将最大化STFC投资的回报。在本提案中，我们将重点关注两个关键过程，其不确定性正在削弱恒星模型的预测能力，在未来三年内，我们可以在这方面取得重大进展，我们在这方面拥有世界领先的专业知识：混合(项目A：Pi Hirschi)和质量损失(项目B：Pi Vink)。我们请求两个分布在两个项目中的PDRA，每个项目都改善了大质量恒星模型中一个关键过程的处理。随着混合和质量损失处理的改进，我们将改进对大质量恒星宇宙影响的预测。特别是，我们将对热点问题进行预测，例如与引力波发射有关的超大质量恒星的最终质量、超新星前体的致密性以及爆炸前活动的可能性。改进后的处理方法将在一个开源的恒星模型代码中实施，很可能成为大质量恒星混合和质量损失的新标准，在天体物理学中有着广泛的应用和影响。

The aim of this Consortium proposal is to improve numerical calculations of the most massive stars in the Universe. Massive stars play a key role through the light they shine and the chemical elements they produce. At the end of their lives, their cores collapse into black holes which, because their gravities are so huge, even light cannot escape from. The lives of massive stars and the related chemistry relate to several key STFC roadmap questions. ``Question A: How did the universe begin and how is it evolving?'': Stars can be used to probe the Universe and its evolution from its infancy, and indeed, the first stars formed only 400 million years after the Big Bang. Even if most of those stars are long dead, their chemical fingerprints are stored in long-lived low-mass extremely metal-poor stars that survive today. Comparing our models to observations of these metal-poor stars provides information about the properties of the first stars and galaxies (question A4) and, more generally, this proposal addresses key questions A5 and A6: ``How do galaxies and stars evolve?''. Stellar models are also used as a theoretical framework for the interpretation of large observational surveys, such as the VLT-Flames survey of massive stars, and to study as-yet unexplained observations. For example, our models weighed the most massive stars discovered to date, and the masses determined (up to 320 solar masses at birth) drastically upsetthe previous upper mass limit of stars. Furthermore, our stellar models will be the main input for supernova simulations. Thus this project also addresses the question: ``D: How can we explore and understand the extremes of the universe?''. Stellar models also provide input for the recentlyopened window of gravitational waves (``D2: gravitational waves properties'') by constraining the masses of gravitational-wave emitting "heavy" black holes. Mass loss is a key process that determines the final mass of massive stars as they lose more than half of their initial constituents via powerful stellar winds.Stellar models provide a crucial theoretical framework for interpretation of data from experimental and observational facilities representing billions of pounds of investments. Theory, however, is lagging behind progress on the observational/experimental side, limiting scientific progress. The stellar models developed in our proposal will provide a crucially needed improved theoretical framework for interpretation of STFC-funded facilities, will make use of STFC's computing facilities, and connect them to STFC-supported nuclearphysics facilities. Our work will thus maximise returns on STFC investment.In this proposal we focus on the two key processes, the uncertainty of which is crippling the predictive power of stellar models, for which great progress can be made in the next three years and for which we have world-leading expertise: mixing (Project A: PI Hirschi) and mass loss (Project B: PI Vink). We request 2 PDRAs distributed across the two projects, each improving the treatment of a key process in massive-star models. With the improved treatment of mixing and mass loss, we willimprove predictions of the cosmic impact of massive stars. In particular we will make predictions concerning hot topics such as final masses of very massive stars linked to gravitational wave emission, compactness of supernova progenitors and the possibility of pre-explosive activity. The improved treatments will be implemented in an open-source stellar modelling code and are likely to become the new standards for mixing and mass loss inmassive stars, with wide ranging applications and impact in astrophysics.