Three-dimensional stellar physics simulations of exotic element formation

观测天文学的进步大大扩展了宇宙中存在的不同类型的丰度模式和化学指纹的图景。在针对早期宇宙中形成的贫金属恒星的大型调查中，现在经常发现具有稀有和奇异丰度模式的恒星。这些恒星丰度观测已经演变成星系考古学的重要工具，用于研究星系的形成和演化，以及早期宇宙的宇宙过程。 这个项目将加深我们对超新星爆炸的奇异恒星演化到黑洞形成过程中元素形成的理解。在大爆炸后不久形成的第一批恒星肯定具有不寻常的元素形成模式，这从在最贫金属元素和最古老的恒星中发现的一些最有趣和最反常的丰度模式中可见一斑。 我们的方法是基于对元素形成的湍流和流体动力学条件的新一代三维模拟。这些模拟需要加拿大计算机公司新的尼亚加拉超级计算机令人印象深刻的计算能力，我们今年早些时候与我们的国际团队一起使用了这台计算机，对大质量恒星中的湍流核心对流进行了最大规模的模拟。 有了这些三维模拟，我们希望能够克服目前一维球对称恒星演化模拟的局限性，这些模拟只通过参数化模型包括湍流混合。通过将核燃烧带来的往往是暴力和能量的反馈纳入到非常高空间分辨率的真实三维模拟中，在模拟运行期间，在给定的时间使用整个尼亚加拉计算机60,000个计算核心的大约一半，我们将产生关于大质量恒星对流壳层湍流条件的独特天体物理模拟数据集，例如C燃烧壳和O燃烧壳的合并。这些模拟将提供一个史无前例的细节，了解这些元素在恒星生命的最后阶段是如何形成的，然后作为超新星爆炸。 我们研究的一个重要目标将是提高我们对大爆炸后形成的第一批大质量恒星中奇异条件的理解，这些恒星是由初始的、原始的和不含金属的物质形成的。一维模型表明，在对流的氢和氦燃烧壳相互作用期间，每单位时间内恒星内部将产生与整个星系产生的能量一样多的能量，尽管当然只是很短的时间。我们的三维模拟将揭示一颗真正的恒星将如何应对这种极端和充满能量的事件。他们将展示在最缺乏金属和最古老的恒星中观察到的异常丰度模式是否以及如何起源于这些第一批恒星。这样，我们的研究将有助于解开早期宇宙中元素的形成和演化之谜。

Advances in observational astronomy have enabled a greatly expanded picture of the different types of abundance patterns and chemical fingerprints that exist in the universe. In large surveys that target metal-poor stars that have formed in the early universe stars with rare and exotic abundance patterns are now frequently found. These abundance observations of stars have evolved into the important tool of galactic archeology to study the formation and evolution of galaxies, and the cosmological processes in the early universe. This project will enhance our understanding of how the elements form in the exotic stellar evolution toward black hole formation of supernova explosion. The first stars that formed shortly after the Big Bang must have possessed yet to be determined unusual modes of element formation as is evident from some of the most intriguing and anomalous abundance patterns found in the most metal-poor and oldest stars. Our approach is based on a new generation of three-dimensional simulations of the turbulent, hydrodynamic conditions of element formation. These simulations require the impressive computing power of Compute Canada's new Niagara supercomputer, that we have used earlier this year together with our international team to perform the largest simulations of turbulent core convection in a massive star. With these three-dimensional simulations we expect to be able to overcome the limitations of present-day one-dimensional spherically-symmetric stellar evolution simulations that include turbulent mixing only via a parameterized model. By including the often violent and energetic feedback from nuclear burning into realistic three-dimensional simulations at very high spatial resolution, using about one half of the entire Niagara computer's 60,000 compute cores at a given time during a simulation run, we will generate unique astrophysics simulation data sets of the turbulent conditions of convective shells in massive stars, such as the merger of a C- and O-burning shell. These simulations will provide a view of unprecedented detail on how the elements form in the final stages of a star's life before exploding as a supernova. An important goal of our research will be to improve our understanding of the exotic conditions in the first massive stars that formed after the Big Bang from the initial, pristine and metal-free material. One-dimensional models suggest that during interactions of convective H- and He-burning shells as much energy per unit time as an entire galaxy produces would be generated inside the star, although of course only for a short time. Our three-dimensional simulations will reveal how a real star would respond to such extreme and energetic events. They will show if and how the anomalous abundance patterns observed in the most metal-poor and oldest stars can originate in these first stars. In this way our research will help to solve the puzzle of element formation and evolution in the early universe.