3-D Simulations of i-Process Nucleosynthesis in the Early Universe

早期宇宙中 i-Process 核合成的 3-D 模拟

• 批准号: 1515792
• 负责人: Paul Woodward
• 金额: $ 2.46万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1515792&HistoricalAwards=false
• 关键词: Simulations; Process; Nucleosynthesis; Early; Universe

Astronomical observations are now probing the early stages of the universe, in which galaxies developed and merged, and the formation of the structures in the universe at the present era was set in motion. An important part of this story is the chemical evolution of galaxies. The formation of the elements in the first stars and their subsequent dispersal are powerful tracers of structure formation and evolution in the early universe. The elements are synthesized deep in the interiors of stars well beyond the reach of direct observation. For this reason, understanding their synthesis and the environment which enables it is clearly in the realm of theory. Although stellar evolution theory is one of the oldest branches of computational science, it has only recently become possible to accurately simulatesome of the key events and processes inside stars that give rise to the heavy elements that are injected back into the interstellar environment rather than being swallowed up in collapsed objects. These events can be quite brief in some cases, lasting only years, days, or even seconds in the case of explosive phenomena. The brevity of these events makes it possible for us now to simulate them in full 3-D detail. This project aims to build a new and powerful capability to simulate these events by coupling together 3-D simulations that cover brief time intervals with 1-D simulations spanning much longer times.This project will simulate processes deep inside stars of the early universe that involve hydrogen ingestion events caused by mixing of material across the boundaries of convection zones. In 1-D stellar evolution simulations, these give rise to rapid hydrogen burning, with enormous energy release and causing nucleosynthesis by neutron capture from neutron fluxes intermediate between the slow (s) and rapid (r) processes. This is the intermediate, or i-process nucleosynthesis that is targeted in this study. Accurate treatment of the convective boundary mixing that drives this i-process requires full 3-D simulation. In some cases that will be addressed, it is possible to simulate the entire event in 3-D. In others, the 3-D simulations performed at intervals as part of a coupled 1-D and 3-D stellar evolution calculation will serve to recalibrate the coefficients in approximate 1-D models for dynamic mixing processes. Such coupled calculations will use these periodic model recalibrations to validate the use of the models as the calculation progresses. When unacceptably large revisions of model "constants" are indicated, a recomputation with 3-D recalibrations taken at shorter time intervals will result. This new process called autocorrecting modeling involves periodic generation of large amounts of 3-D data from simulation codes. This data generation is followed by a detailed analysis of the data in terms of 1-D models. The results of this analysis are then fed back into the 1-D stellar evolution computation. In the process of carrying out the simulations a large database of results from 3-D simulations of convective boundary mixing in stellar interiors will be generated. This database will be organized so that the simulation codes can mine it automatically, comparing it to a variety of potentially useful 1-D models of the mixing process. This database, together with the tools that mine it, analyze it, and display results, will be unique. It will represent a significant investment, not only in our time developing the simulation codes and data analysis and visualization tools, but also in computer time on one of the most powerful computing systems in the world. A broad impact of this project will therefore be this database and tools that make it useful in stellar evolution research. The project will result in the development of new, automated techniques for data-enabled science but in addition to these techniques an important outcome will be the data itself which will be made available to the community on-line in a useful format. The hydrodynamics simulations will enable the clarification of the nucleosynthetic yields of the i-process in early generations of stars. The PI will work with the NuGrid collaboration to see that the results become incorporated into data sets that are available to the community for chemical evolution simulations of galaxies and structures in the early universe. The PI is also collaborating with the scientists at NSF?s Joint Institute for Nuclear Astrophysics (JINA). A further impact of this work will be to perform the detailed simulations that allow the assessment of the impact of these new rate measurements on nucleosynthesis, so that it can be compared with observables such as spectra of metal-poor stars in globular clusters and isotopic compositions of pre-solar grains.

天文观测现在正在探索宇宙的早期阶段，其中星系发展并合并，并开始了当今时代宇宙结构的形成。这个故事的一个重要部分是星系的化学演化。第一批恒星中元素的形成及其随后的扩散是早期宇宙结构形成和演化的有力示踪剂。这些元素是在恒星内部深处合成的，远远超出了直接观察的范围。因此，理解它们的合成和实现它的环境显然属于理论领域。尽管恒星演化理论是计算科学最古老的分支之一，但直到最近才能够准确模拟恒星内部的一些关键事件和过程，这些事件和过程产生重元素，这些重元素被注入回星际环境而不是被吞噬倒塌的物体中。在某些情况下，这些事件可能非常短暂，仅持续数年、数天，甚至在爆炸现象的情况下持续数秒。这些事件的短暂性使得我们现在能够以完整的 3D 细节来模拟它们。该项目旨在通过将涵盖短暂时间间隔的 3-D 模拟与跨越更长时间的 1-D 模拟结合在一起，建立一种新的强大功能来模拟这些事件。该项目将模拟早期宇宙恒星深处的过程，其中涉及由跨对流区边界的材料混合引起的氢摄入事件。在一维恒星演化模拟中，这些会引起氢的快速燃烧，释放出巨大的能量，并通过从慢速（s）和快速（r）过程之间的中子通量中捕获中子来引起核合成。这是本研究针对的中间体或 i 过程核合成。精确处理驱动此 i 过程的对流边界混合需要完整的 3D 模拟。在某些将要解决的情况下，可以以 3D 方式模拟整个事件。在其他情况下，作为耦合的 1-D 和 3-D 恒星演化计算的一部分，每隔一段时间执行 3-D 模拟将有助于重新校准动态混合过程的近似 1-D 模型中的系数。随着计算的进行，这种耦合计算将使用这些定期模型重新校准来验证模型的使用。当模型“常数”出现不可接受的大修改时，将导致以更短的时间间隔进行 3D 重新校准的重新计算。这种称为自动校正建模的新过程涉及从模拟代码定期生成大量 3D 数据。生成数据后，根据一维模型对数据进行详细分析。然后，该分析的结果被反馈到一维恒星演化计算中。在进行模拟的过程中，将生成恒星内部对流边界混合 3D 模拟结果的大型数据库。该数据库将被组织起来，以便模拟代码可以自动挖掘它，并将其与混合过程的各种潜在有用的一维模型进行比较。该数据库以及挖掘、分析和显示结果的工具将是独一无二的。这将是一项重大投资，不仅是我们开发模拟代码、数据分析和可视化工具的时间，也是世界上最强大的计算系统之一的计算机时间的投资。因此，该项目的广泛影响将是使其在恒星演化研究中发挥作用的数据库和工具。该项目将导致数据驱动科学的新自动化技术的开发，但除了这些技术之外，一个重要的成果将是数据本身，这些数据将以有用的格式在线提供给社区。流体动力学模拟将能够澄清早期恒星 i 过程的核合成产率。 PI 将与 NuGrid 合作，将结果纳入数据集中，供社区用于早期宇宙中星系和结构的化学演化模拟。 PI 还与 NSF 核天体物理联合研究所 (JINA) 的科学家合作。这项工作的进一步影响将是进行详细的模拟，以评估这些新的速率测量对核合成的影响，以便可以将其与球状星团中贫金属恒星的光谱和同位素组成等可观测数据进行比较前太阳粒子。

项目成果

Simulating Stellar Hydrodynamics at Extreme Scale

模拟极端规模的恒星流体动力学

• DOI: 10.1109/mcse.2018.05329811
• 发表时间: 2018-09
• 期刊: Computing in Science & Engineering
• 影响因子: 2.1
• 作者: Woodward, Paul R.;Herwig, Falk;Wetherbee, Ted
• 通讯作者: Wetherbee, Ted