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: 1440025
• 负责人: Paul Woodward
• 金额: $ 1.54万
• 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: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1440025&HistoricalAwards=false
• 关键词: Simulations; Process; Nucleosynthesis; Early; Universe

Astronomical observations are now probing the early stages of the universe, in which galaxiesdeveloped and merged, and the formation of the structures in the universe at the present erawas set in motion. An important part of this story is the chemical evolution of galaxies. Theformation of the elements in the first stars and their subsequent dispersal are powerful tracersof structure formation and evolution in the early universe. This project involves the simulationof processes deep inside stars of the early universe that experience hydrogen ingestionevents caused by mixing of material across the boundaries of convection zones. In 1-D stellarevolution simulations, these give rise to rapid hydrogen burning, with enormous energy releaseand causing nucleosynthesis by neutron capture from neutron fluxes intermediate between theslow (s) and rapid (r) processes. This is the intermediate, or i-process nucleosynthesis thatis targeted in this study. Accurate treatment of the convective boundary mixing that drivesthis i-process requires full 3-D simulation. The rapid hydrogen burning that ensues, togetherwith the very large luminosities involved make 3-D simulation affordable on NSF?s powerfulnew supercomputing platform, Blue Waters, at NCSA.A new and powerful capability will be built in this project to simulate these events by couplingtogether 3-D simulations that cover brief time intervals with 1-D simulations spanning muchlonger times. In some cases that will be addressed, it is possible to simulate the entire eventin 3-D. In others, 3-D simulations performed at intervals as part of a coupled 1-D and 3-Dstellar evolution calculation will serve to recalibrate the coefficients in approximate 1-D modelsfor dynamic mixing processes. Such coupled calculations will use these periodic modelrecalibrations to validate the use of the models as the calculation progresses. When unacceptablylarge revisions of model "constants" are indicated, a recomputation with 3-D recalibrationstaken at shorter time intervals will result. This new process is called autocorrecting modeling.It involves periodic generation of large amounts of 3-D data from simulation codes. This datageneration is followed by a detailed analysis of the data in terms of 1-D models. The resultsof this analysis are then fed back into the 1-D stellar evolution computation. Pioneering thisnew approach is a major challenge of the project; the database of condensed simulation resultsthat will be built in the process will be a significant outcome of the project. This data will bemade available first to collaborators and ultimately to the broad community. It will be possibleto use this data to formulate, validate, and refine simplified models of the convective boundarymixing processes that are a major focus of this study. It will also be possible for others,potentially using quite different simulation software, to use this data to adopt an autocorrectingmodeling approach in studies of related problems. In the first year of this project, a continuationof present work with the well observed case of Sakurai's object is planned along with applicationof the new techniques to simulations of low-mass, low-metallicity AGB stars.

天文观测现在正在探索宇宙的早期阶段，其中星系发展和合并，并且当前时代宇宙结构的形成已经开始。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。该项目涉及模拟早期宇宙恒星深处的过程，这些过程经历了由于物质跨越对流区边界混合而引起的氢吸收事件。在一维恒星公转模拟中，这些会引起氢的快速燃烧，释放大量能量，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。随后发生的快速氢气燃烧，加上所涉及的非常大的光度，使得 3D 模拟可以在 NSF 强大的新超级计算平台 Blue Waters 上进行，该平台位于 NCSA。该项目将建立一个新的强大功能，通过耦合在一起来模拟这些事件3-D 模拟涵盖短暂的时间间隔，而 1-D 模拟则涵盖更长的时间。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，每隔一定时间执行 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。这个新过程称为自动校正建模。它涉及从模拟代码定期生成大量 3D 数据。该数据生成之后是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。 开创这种新方法是该项目的主要挑战；在此过程中建立的压缩模拟结果数据库将是该项目的重要成果。 这些数据将首先提供给合作者，并最终提供给广大社区。 可以使用这些数据来制定、验证和完善对流边界混合过程的简化模型，这是本研究的主要重点。 其他人也可能使用完全不同的模拟软件，使用这些数据在相关问题的研究中采用自动校正建模方法。 在该项目的第一年，计划继续目前对樱井天体进行良好观测的工作，并将新技术应用于低质量、低金属丰度 AGB 恒星的模拟。

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