Searching for missing matter in the Universe using advanced computer simulations and synthetic observations

Devin Silvia博士被授予美国国家科学基金会天文学和天体物理学博士后奖学金，在密歇根州立大学开展研究和教育项目。从第一颗恒星在灾难性的超新星爆炸中结束生命的那一刻起，比氢和氦重的元素就一直在“污染”大爆炸遗留下来的原始气体。从一个只包含氢和氦的简单宇宙到我们今天所知道的富含构成生命的元素的宇宙，了解这种进化的本质对天体物理学界来说是非常有兴趣的。然而，准确地建模和理解这一过程已被证明是困难的。西尔维娅博士开展的研究项目旨在解决一个特别的谜团：为什么宇宙中的一些物质似乎随着宇宙时间的流逝而消失了？虽然观测天文学家已经努力使用强大的哈勃太空望远镜（HST）来定位这种物质，但它的大部分仍然无法被探测到。西尔维娅博士将使用最先进的宇宙模拟技术精确追踪宇宙中的物质并计算其物理特性。通过使用这些模拟的结果来产生模拟HST捕获的合成观测结果，西尔维娅博士将能够回答这个问题：失踪的物质藏在哪里？除了这个研究项目外，西尔维亚博士还致力于通过开发和教授一门新的天文学课程来解决STEM学科中明显缺乏多样性的问题，该课程将利用创新的教育实践来提高学习者作为STEM社区成员的认同感。本课程还将为学习者提供对科学主题的持久理解和对观察到的现象进行批判性思考的能力。理解星系间介质化学演化的一个重大障碍是将类星体吸收谱线的观测结果转化为对金属含量的可靠估计。为了解决这一障碍，这项工作的主要目标将是表征星系间和星系周围介质的质量含量和电离特性，并使用结果来解释当前的观测结果并为未来的观测提供信息。PI将通过执行一套最先进的宇宙学模拟来实现这些目标，该模拟采用了一种新开发的化学网络求解器，可以对星系间和星系周围介质的电离结构进行非平衡计算。通过完成模拟，PI将利用一种新技术来生成合成类星体吸收谱线，并将结果与哈勃太空望远镜宇宙起源光谱仪的观测结果进行比较。然后，PI将编制一份目录，将光谱特征与产生它们的物理条件联系起来。除了这个研究项目，PI还计划为一年级本科生设计和教授一门新的课程，该课程以天文学主题为重点，采用探究式学习的元素。与传统的教学实践不同，以探究为基础的教学方法可以非常有效地创造对科学主题的持久理解，并增加各种背景的学生作为STEM社区成员的可能性。

Dr. Devin Silvia is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at Michigan State University. From the moment the first star ended its life in a catastrophic supernova explosion, elements heavier than hydrogen and helium have been "polluting" the once pristine gas left over from the Big Bang. Understanding the nature of this evolution from a simple universe containing only hydrogen and helium to the one we know today, rich with the elements that have become the building blocks of life, is of great interest to the astrophysics community. However, accurately modeling and understanding this process has proven difficult. The research program to be carried out by Dr. Silvia is aimed at solving one particular mystery: why does some of the matter in the Universe appear to go missing as a function of cosmic time? While observational astronomers have endeavored to locate this matter using the powerful Hubble Space Telescope (HST), much of it continues to elude detection. Dr. Silvia will employ state-of-art cosmological simulations capable of accurately tracking the matter contained in the Universe and calculating its physical properties. By using the results of these simulations to produce synthetic observations that mimic those captured by the HST, Dr. Silvia will be able to answer the question: where is the missing matter is hiding? Alongside this research program, Dr. Silvia is driven to address the apparent lack of diversity within STEM disciplines by developing and teaching a new astronomy course that will leverage innovative educational practices shown to increase learners' identification as members of the STEM community. The course will also serve to provide learners with an enduring understanding of scientific topics and the ability to think critically about observed phenomena.A significant obstacle in understanding the chemical evolution of the intergalactic medium is turning observations of quasar absorption lines into reliable estimates of metal content. In an effort to address this obstacle, the primary objectives of this work will be to characterize the mass content and ionization properties of the intergalactic and circumgalactic media and use the results to interpret current observations and inform future ones. The PI will meet these objectives by carrying out a suite of state-of-the art cosmological simulations that employ a newly-developed chemical network solver, enabling non-equilibrium calculations of the ionization structure of the intergalactic and circumgalactic media. Using completed simulations, the PI will leverage a novel technique for generating synthetic quasar absorption line spectra and compare the results to observations from the Hubble Space Telescope's Cosmic Origins Spectrograph. The PI will then compile a catalog that links spectral features to the physical conditions that generated them. Alongside this research program, the PI plans to design and teach a new course for first year undergraduate students that focuses on topics in astronomy and is built using the elements of inquiry-based learning. Distinct from traditional teaching practices, an inquiry-based approach to teaching and learning can be very effective at creating an enduring understanding of scientific topics and increasing the likelihood that students of all backgrounds identify as members of the STEM community.