Collaborative Research: Rethinking the Fundamentals of Massive Star Clusters

球状星团是一个由成千上万颗恒星组成的紧密集团，它们被引力束缚在一起。有数百个球状星团围绕着我们的银河系运行。球状星团就像化石一样，在星系刚刚开始形成的最早时期，追踪宇宙中的条件。在单个球状星团之间观察到有趣的差异，这为我们的银河系的形成提供了线索。在球状星团恒星中，属于不同化学元素的原子浓度变化的方式挑战了关于恒星年龄，起源和生命周期的传统智慧。调查人员将与世界上的一些观察？主要工作包括：（a）发展一个统一的星团自我浓缩的假设;（b）透过新的动力学和恒星族群调查，了解球状星团的恒星组成;（B）研究恒星的演化和演化。（c）在球状星团质量函数的最大值上研究球状星团与星系之间的关系。将进行新的光学和近红外光度和光谱观测，以探索可测量的量（如质光比和丰度异常）如何取决于年龄，金属丰度，恒星初始质量函数和动力学演化。有趣的趋势，其中许多混淆了标准的解释，已经被确定：1）自富集似乎涉及在银河系球状星团的丰度分布和在河外球状星团系统中发现的质量-金属丰度关系; 2）观察到的星系恒星晕的性质，并在中期年龄集群的气体的初步测量，每一个挑战的青睐自富集机制; 3）质光比对金属丰度的依赖性与恒星演化模型的预期相反; 4）一个不断扩大的致密恒星系统的动物园已经被确定，包括超致密矮星，它们可能是由矮星系的潮汐剥离或球状星团合并形成的; 5）超致密矮星的质光比升高可能是由大质量中心黑洞解释的。研究人员将澄清这些问题，测试恒星演化和人口合成模型，并追踪紧凑恒星系统的起源。由于球状星团比以前认识到的更复杂，了解它们的性质以及它们与其他类型恒星系统的关系在天体物理学中具有广泛的意义。从球状星团得出的推论为恒星、星系、黑洞和暗物质的形成和演化提供了理论依据。这一基础性工作影响了从星星形成到宇宙学的前沿研究。为了有效地促进这项研究的广泛影响，与非营利组织的伙伴关系，？科学伙伴？将继续进行。这个非常成功的试点项目已经吸引了数千名来自不同背景的K-12学生，包括弱势群体。专业和公共宣传的一个强有力的计划将继续下去，包括妇女，本科生和少数民族在前沿研究的证明记录。将扩大一个成功的试点计划，让本科生参与大规模集群研究。学生和博士后将接受优秀的培训，获得世界一流的设施和高级研究人员，参与研究过程的各个方面。新发现的紧凑恒星系统及其基本性质的用户友好的遗留目录将在网上公开提供。

A Globular Cluster is a tight group of hundreds of thousands of stars bound together by gravity. There are hundreds of Globular Clusters orbiting around our own Milky Way galaxy. Globular Clusters serve as fossils that trace conditions in the universe at the earliest times, when galaxies were just starting to form. Intriguing differences are observed between individual Globular Clusters, which provide clues about the formation of our Galaxy. In Globular Cluster stars, the concentrations of atoms belonging to different chemical elements vary in ways that challenge conventional wisdom about the ages, origins and life cycles of stars. The investigators will make observations with some of the world?s largest and best-equipped telescopes to test theoretical models of how stars, star clusters and galaxies come to be.The principal work involves (a) developing a unified scenario for self-enrichment among star clusters; (b) understanding the stellar content of Globular Clusters through novel dynamical and stellar population investigations; and (c) studying the relationship between Globular Clusters and galaxies at the extreme upper limit of the Globular Cluster mass function. New optical and near-infrared photometric and spectroscopic observations will be made to explore how measurable quantities (such as mass-to-light ratios and abundance anomalies) depend on age, metallicity, stellar initial mass function, and dynamical evolution. Intriguing trends, many of which confound standard interpretations, have already been identified: 1) self-enrichment appears to be implicated in abundance spreads in Galactic Globular Clusters and in a mass-metallicity relation found in extragalactic Globular Cluster systems; 2) observed properties of galaxy stellar halos, and initial measurements of gas in intermediate-age clusters, each challenge the favored mechanism for self-enrichment; 3) the dependence of mass-to-light ratio on metallicity is opposite to that expected from stellar evolution models; 4) an expanding zoo of compact stellar systems has been identified, including ultra compact dwarfs, that could be formed either by tidal stripping of dwarf galaxies or from Globular Cluster mergers; 5) the elevated mass-to-light ratios of ultra compact dwarfs may be explained by massive central black holes. The investigators will clarify each of these issues, test stellar evolution and population synthesis models, and trace the origins of compact stellar systems.Since Globular Clusters are more complex than formerly realized, understanding their properties and how they relate to other types of stellar systems has wide implications in astrophysics; inferences drawn from Globular Clusters inform theories of the formation and evolution of stars, galaxies, black holes, and dark matter. This fundamental work impacts forefront research from star formation to cosmology. To promote the broader impacts of this research effectively, the partnership with the non-profit organization, ?Science Buddies?, will be continued. This highly successful pilot program has already engaged thousands of K-12 students from diverse backgrounds, including disadvantaged groups. A vigorous program of professional and public outreach will continue, with a proven record of including women, undergraduates, and minorities in forefront research. A successful pilot program to involve undergraduates in Massive Clusters research will be expanded. Students and post-docs will receive excellent training with access to world-class facilities and to senior researchers, participating in all aspects of the research process. A user-friendly, legacy catalog of newly discovered compact stellar systems and their fundamental properties will be publicly available online.