The Early Evolution of Star Clusters and their Stellar Populations

星团及其恒星群的早期演化

• 批准号: RGPIN-2014-03833
• 负责人: Sills, Alison
• 金额: $ 2.26万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=633390
• 关键词: Early; Evolution; Star; Clusters; their

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.

恒星簇是数十至数百万颗星的群体。它们在所有星系中都发现，用于追踪星系的形成和结构。但是，我们对集群生活的早期阶段的理解是不完整的。很难观察到年轻的明星簇，因为它们通常很远，并且总是被气体和灰尘笼罩。大多数模型都认为，恒星簇的形成非常快，所有恒星都完全在球形系统中出生，并且这些恒星形成的所有气体不再存在。从观察上讲，我们知道这些假设都不正确，但是它们被用于使以前的模拟更加易于处理。但是，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理解簇及其星星的早期演变方面取得重大进步。大型恒星簇的模型假设它们的恒星都同时在同一位置和同一材料中形成。然而，最近，观察结果表明这些簇有多个恒星种群。期望第一代的一些较短的恒星产生并污染了当时形成第二代的气体，但并不是以与银河系其余部分形成的恒星形成的方式相同。关于年轻簇中第二代气体的性质和行为，恒星的形成方式和位置以及两代方式相互作用的开放问题仍然存在。此外，星形簇拥有许多不同种类的“恒星式”，这些恒星的发展方式与像我们的太阳这样的普通单星的发展方式不相同。对这些人群进行建模的最新进展表明，动态相互作用和二进制进化都需要了解群集中此类系统的特性。研究非常年轻的集群，破解“多个人群”问题并建模出色的Exotica分享了一些相同的挑战。它们是多方面的问题：为了正确解释观测值，我们必须了解恒星及其发展方式。同时，我们必须利用对流体动力学的理解来跟随系统中的气体，例如，质量从一颗恒星转移到另一颗星，或者是由于污染者发出的气体以在簇中创建第二代。我们永远不会只处理一个孤立的恒星，而必须考虑许多恒星的引力。因此，还必须包括出色的动力学。这些天体物理学区域中的每一个都有其自然的时间尺度，距离尺度和能量尺度。因此，首先近似，每个区域都可以独立地应用于星团。因此，我们对恒星集群及其恒星种群的理解相当不错，但并不完整。多亏了最近的大量观察数据，我们现在了解到，我们必须采用更复杂的多时间，多物理学模型。在这项建议中，我描述了这种新颖的恒星天体物理学方法将如何应用于非常年轻的恒星群的研究。我们将恒星动力学与恒星在簇中丢失的气体的流体动力学模型相结合，以了解在第一代恒星存在下如何形成第二代。我们将研究附近星系中此类区域的X射线和红外观测，这是非常年轻的簇的结构特性。我们是世界上为数不多的群体之一，他们可以为建模星团的早期演变提供这种全面的方法，我们希望接下来的5年特别成果。