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.

现在，天文观测正在探测星系发展和合并的宇宙的早期阶段，并且在当今时代的宇宙中形成了宇宙的结构。这个故事的重要部分是星系的化学演化。第一颗恒星中元素的形成及其随后的散布是早期宇宙中结构形成和进化的强大示踪剂。这些元素在恒星内部的深处合成，远远超出了直接观察的范围。因此，理解它们的综合和能够显然是理论领域的环境。尽管恒星进化论是计算科学的最古老的分支之一，但直到最近才有可能准确地模拟恒星内部的关键事件和过程，这些事件和过程产生了重新注入的重型元素，而不是被注入了星际环境而不是被吞噬在折叠的对象中。在某些情况下，这些事件可以很短，在爆炸性现象的情况下持续仅几年，几天甚至几秒钟。这些事件的简洁性使我们现在有可能以完整的3D细节模拟它们。该项目旨在建立一个新的强大能力，通过将3-D模拟结合在一起，以涵盖短时间间隔的1-D模拟范围更长的时间来模拟这些事件。该项目将模拟涉及的早期宇宙中深处的过程，这些过程涉及通过在对流区域的边界中混合材料引起的氢摄入事件。在1-D恒星演化的模拟中，这些模拟引起了快速氢的燃烧，并释放了巨大的能量，并引起了中子磁通中的中子量中的核合成，中间的慢速（S）和快速（R）过程中介导。这是本研究中针对的中间或I过程。对对流边界混合的准确处理，该混合驱动了这种IPROCESS需要完整的3D模拟。在某些情况下，将要解决的情况，可以在3-D中模拟整个事件。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进行的3D模拟将用于重新校准动态混合过程的大约1-D模型中的系数。此类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。当指示模型“常数”的大量修订时，会导致以较短时间间隔进行3D重新校准的重新计算。这个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3-D数据。该数据生成之后是根据1-D模型对数据的详细分析。然后将该分析的结果反馈到1-D恒星演化计算中。在进行模拟的过程中，将生成来自恒星内饰中对流边界混合的3-D模拟结果的大数据库。该数据库将组织起来，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1D模型进行比较。该数据库以及挖掘它，分析并显示结果的工具将是唯一的。这将代表一项重大投资，不仅在我们开发模拟代码，数据分析和可视化工具的时代，而且在世界上最强大的计算系统之一的计算机时间内。因此，该项目的广泛影响将是该数据库和工具，使其在恒星进化研究中有用。该项目将导致开发新的，具有数据支持科学的自动化技术，但是除了这些技术外，重要的结果将是数据本身，该数据本身将以有用的格式在线提供给社区。流体动力学模拟将阐明在几代恒星中I过程的核合成产量。 PI将与Nugrid合作合作，以确保结果已纳入社区可用于早期宇宙中星系和结构的化学演化模拟的数据集中。 PI还与NSF核天体物理学联合研究所（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，以评估这些新速率测量对核合成的影响，以便可以将其与可观察到的无观测值进行比较晶粒前晶粒。