The Early Evolution of Star Clusters and their Stellar Populations

星团是由数千万到数百万颗恒星组成的群体。它们存在于所有星系中，用于追踪星系的形成和结构。然而，我们对星团形成的早期阶段的了解还很不完整。年轻的星团很难被观测到，因为它们通常距离很远，而且总是被气体和尘埃包裹着。大多数模型假设星团形成得非常快，所有的恒星都在一个球形系统中同时诞生，而形成这些恒星的所有气体都不再存在。从观测上看，我们知道这些假设都不正确，但它们被用来使以前的模拟更容易处理。然而，由于我们在恒星天体物理学不同领域的专业知识，我的小组现在准备在我们对星团及其恒星的早期演化的理解方面取得重大进展。**大质量星团的模型假设它们的恒星都是在同一时间、同一地点、由相同的物质形成的。然而，最近的观测显示，这些星团有多个恒星群。我们的预期是，第一代中寿命较短的一些恒星产生并污染了随后形成第二代恒星的气体，但与银河系中其他几代恒星形成的方式不同。关于年轻星团中第二代气体的性质和行为，恒星是如何和在哪里形成的，以及这两代气体是如何相互作用的，仍然存在一些悬而未决的问题。此外，星团还拥有许多不同种类的“外来恒星”，这些恒星的演化方式与像太阳这样的普通单星不同。最近对这些种群建模的进展表明，要了解集群中这类系统的特性，需要动态相互作用和二元演化。**研究非常年轻的星团，破解“多种群”问题和模拟外来恒星有一些相同的挑战。它们是多方面的问题：为了正确地解释观测结果，我们必须了解恒星以及它们是如何演化的。与此同时，我们必须利用我们对流体力学的理解来跟踪系统中的气体，例如，当质量从一颗恒星转移到另一颗恒星时，或者当污染者排放气体以在星团中产生第二代恒星时。我们处理的绝不是一颗孤立的恒星，而必须考虑到许多恒星的引力。因此，恒星动力学也必须包括在内。天体物理学的每一个领域都有自己的自然时间标度、距离标度和能量标度。因此，近似地说，每个区域都可以独立地应用于星团。正因为如此，我们对星团及其恒星群的理解相当好，但还不完整。由于最近大量的观测数据，我们现在明白，我们必须转向更复杂的多时间尺度、多物理场建模。**在这个提议中，我描述了这种新的恒星天体物理学方法将如何应用于非常年轻的星团的研究。我们将把恒星动力学与星团中恒星丢失的气体的流体动力学模型结合起来，以了解它是如何在第一代恒星存在的情况下形成第二代的。我们将研究非常年轻的星团的结构特性，这是由附近星系中这些区域的x射线和红外观测引起的。我们是世界上为数不多的能够提供这种综合方法来模拟星团早期演化的团队之一，我们预计未来5年将取得特别丰硕的成果。

Star clusters are groups of tens to millions of stars. They are found in all galaxies and are used to trace galaxy formation and structure. However, our understanding of the early stages of a cluster's life is quite incomplete. Young star clusters are hard to observe, as they are often far away and always enshrouded in gas and dust. Most models assume that star clusters were formed very quickly, with all stars born at exactly the same time, in a spherical system, and that all the gas from which these stars formed is no longer present. Observationally, we know none of these assumptions are correct, but they were used in order to make previous simulations more tractable. However, because of our expertise in different areas of stellar astrophysics, my group is now poised to make significant advances in our understanding of the early evolution of clusters and their stars. **Models of massive star clusters have assumed that their stars all formed at the same time, in the same place, and out of the same material. Recently, however, observations are showing us that these clusters have multiple stellar populations. The expectation is that some of the shorter-lived stars of the first generation produced and polluted the gas which then formed the second generation, but not in the same way that generations of stars are formed in the rest of the galaxy. Open questions still remain about the properties and behaviour of the second generation gas in young clusters, how and where the stars formed, and how the two generations interacted. In addition, star clusters host many different kinds of "stellar exotica", stars which do not evolve in the same way as normal single stars like our Sun. Recent advances in modelling these populations have shown that both dynamical interactions and binary evolution are required to understand the properties of such systems in clusters.**Studying very young clusters, cracking the "multiple populations" problem and modelling stellar exotica share some of the same challenges. They are multifaceted problems: in order correctly interpret the observations, we must understand stars and how they evolve. At the same time, we must use our understanding of hydrodynamics to follow the gas in the system, for example as mass is transferred from one star to another, or as gas is emitted by the polluters to create a second generation in clusters. We are never dealing with just one isolated star, but must consider the gravitational forces of many stars. Therefore, stellar dynamics must also be included. Each of these areas of astrophysics has its own natural timescale, distance scale, and energy scale. Therefore, to first approximation, each area can be applied to star clusters independently. Because of this, our understanding of stellar clusters and their stellar populations is quite good, but it is not complete. Thanks to the recent wealth of observational data, we now understand that we must move to more complicated multi-timescale, multi-physics modelling.**In this proposal, I describe how this novel approach to stellar astrophysics will be applied to the study of very young stellar clusters. We weill combine stellar dynamics with hydrodynamical models of the gas lost by stars in clusters to understand how it can form a second generation in the presence of the first generation stars. We will investigate the structural properties of very young clusters, prompted by X-ray and infrared observations of such regions in the nearby galaxy. We are one of the few groups in the world who can provide this comprehensive approach to modelling the early evolution of star clusters, and we expect the next 5 years to be particularly fruitful.