权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

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

基本信息

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

项目摘要

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，在这个阶段中，星系发展和合并，并开始形成当今宇宙的结构。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线索。这些元素是在恒星内部深处合成的，远远超出了直接观测的范围。出于这个原因，理解它们的综合以及使其成为可能的环境显然属于理论范畴。虽然恒星演化理论是计算科学最古老的分支之一，但直到最近才有可能准确地模拟恒星内部的一些关键事件和过程，这些事件和过程导致重元素被注入星际环境，而不是被坍缩的物体吞噬。在某些情况下，这些事件可能非常短暂，在爆炸现象中仅持续数年、数天甚至数秒。这些事件的短暂性使我们现在有可能以完整的三维细节来模拟它们。该项目旨在通过将涵盖短时间间隔的三维模拟与跨越更长时间的一维模拟结合起来，建立一种新的强大能力来模拟这些事件。该项目将模拟早期宇宙恒星内部深处的过程，其中涉及对流区边界上物质混合引起的氢摄入事件。在一维恒星演化模拟中，这些会引起快速的氢燃烧，释放出巨大的能量，并通过从慢（s）和快（r）过程之间的中子通量中捕获中子而引起核合成。这是本研究中的目标中间体或i-过程核合成。准确处理驱动这一i-过程的对流边界混合需要完全的3-D模拟。在某些情况下，将被解决，它是可能的，以模拟整个事件的3-D。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，每隔一段时间进行的3-D模拟将用于重新校准近似1-D模型中的动态混合过程系数。这种耦合计算将使用这些周期性的模型重新校准来验证随着计算的进行模型的使用。当指示对模型“常数”进行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。这个新的过程被称为自动校正建模，包括从模拟代码中定期生成大量的3D数据。数据生成之后，根据1-D模型对数据进行详细分析。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，将产生恒星内部对流边界混合三维模拟结果的大型数据库。该数据库将被组织，以便模拟代码可以自动挖掘它，将其与混合过程的各种潜在有用的一维模型进行比较。这个数据库，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，不仅在我们开发模拟代码和数据分析和可视化工具的时间，而且在世界上最强大的计算系统之一的计算机时间。因此，这个项目的广泛影响将是这个数据库和工具，使其在恒星演化研究中有用。该项目将导致开发新的自动化技术，用于数据驱动的科学，但除了这些技术之外，一个重要的成果将是数据本身，它将以有用的格式在线提供给社区。流体动力学模拟将使澄清的核合成产量的i-过程中的早期世代的恒星。PI将与NuGrid合作，将结果纳入可供社区用于早期宇宙中星系和结构化学演化模拟的数据集。PI还与NSF的科学家合作？核天体物理联合研究所（JINA）。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太阳前颗粒的同位素组成等可观测数据进行比较。