The Missing Link: Unlocking galaxy evolution by understanding star formation.

恒星是推动星系演化的引擎。当大质量恒星死亡时，由此产生的超新星爆炸将能量传递给星系中的气体，并支持它免受引力坍缩的影响。恒星通过核聚变形成所有比氦重的元素，这些元素在超新星爆炸中返回星系。行星是恒星形成的副产品，它们释放的能量可能为这些行星上的生命提供燃料。了解恒星是如何形成的，对于理解宇宙大爆炸以来星系的演化至关重要。我们可以使用革命性的新望远镜来测试这个过程，比如阿塔卡马大型毫米和亚毫米阵列（ALMA）和未来的平方公里阵列（SKA）。这些先进的设备将使以前所未有的细节观察其他星系内的不同环境成为可能。为了解开其他星系中恒星如何形成的谜团，我们首先需要能够与观测结果进行比较的良好预测。我想通过使用超级计算机模拟来创建非常详细的模型来帮助解开这个谜团，这些模型是关于气体在不同类型的星系中集中成云的地方。这些气体云被称为分子云，因为它们主要由氢分子组成，是恒星诞生的摇篮。我将使用这些模型来预测温度、密度、化学成分和气体运动，然后研究气体坍塌形成恒星的容易程度、形成恒星的类型以及不同星云中恒星的数量。这将使我能够确定分子云和其中形成的恒星是否在任何地方都是相同的，或者它们是否随星系环境而变化。这是一个重要的假设，因为在观测中，我们只能看到其他星系中最亮的恒星，并且必须假设较暗的恒星形成的比例与我们在银河系附近的恒星形成区域中看到的比例相同。以前的恒星形成模型总是从简单的云如何开始的估计开始，但独特的是，这个项目使用了实际的星系模型。一个主要的创新是，我将使用一个化学模型来预测气体的组成，这将决定望远镜看到的发射。例如，ALMA对一氧化碳气体的发射很敏感，而SKA对氢原子的发射很敏感。利用这个项目产生的计算机模拟，我将对其他星系中的分子云进行综合观测。我们知道，在其他星系中，气体的数量、星系的结构和化学成分可能会有所不同，因此观测到的云的样子也会有所不同。我们可以将计算机生成的发射图与观测到的图进行比较，作为参考指南，以确定观测到的云的实际属性。天文观测是三维结构的二维投影图像，此外，发射的光随着气体的温度和密度而变化。这使得分子云很难理解没有一个好的模型来比较。现代望远镜尤其如此，因为它们提高了分辨率和灵敏度，观测结果非常复杂，因为它们可以看到精细的细节。因此，这个项目的模型对于使用ALMA和SKA来确定我们宇宙中的恒星是如何形成的至关重要。

Stars are the engines that drive how galaxies evolve. When massive stars die the resulting supernova explosions transfer energy to the gas in the galaxy and support it against gravitational collapse. Stars form all the elements heavier than Helium by nuclear fusion, and these elements are returned to the galaxy in the supernova explosions. Planets are formed as by-products of star-formation, and the energy that they emit may fuel life on those planets. An understanding of how stars form is crucial to understanding the evolution of galaxies since the Big Bang. We can test this process using revolutionary new telescopes like the Atacama Large Millimetre and sub-millimetre Array (ALMA) and the future Square Kilometre Array (SKA). These advanced facilities will make it possible to observe the different environments within other galaxies in unprecedented detail.To solve the mystery of how stars form in other galaxies we will first need good predictions that can be compared against the observations. I want to help solve this mystery by using supercomputer simulations to create extremely detailed models of where gas is concentrated into clouds in different types of galaxies. These gas clouds are known as molecular clouds, because they mainly consist of hydrogen molecules, and are the stellar nurseries in which stars are born. I will use the models to predict the temperature, density, chemical composition, and gas motions, and then investigate how easily the gas collapses to form stars, the type of stars formed, and the numbers of stars in the different clouds. This will enable me to determine whether molecular clouds and the stars formed in them are the same everywhere, or whether they vary with galactic environment. This is an important assumption as in observations we can only see the very brightest stars in other galaxies and have to assume that the fainter stars form in the same proportion as we see in nearby star-forming regions in our own Milky-Way Galaxy.Previous models of star-formation always started with simple estimates of how clouds might begin, but uniquely, this project uses actual galaxy models. A major innovation is that I will use a chemical model to predict the composition of the gas, which will determine the emission seen by a telescope. For example, ALMA is sensitive to the emission from carbon monoxide gas, and the SKA will be sensitive to emission from atomic hydrogen. Using the computer simulations generated from this project I will make synthetic observations of the molecular clouds in other galaxies. In other galaxies we know that the amount of gas, the structure of the galaxy, and the chemical composition may be different, and so how clouds appear when observed will also be different. We can compare the computer generated emission maps to the observed maps as a reference guide to determine what the properties of the observed clouds actually are. Astronomical observations are 2D projected images of what are 3D structures, moreover, the emitted light changes with the temperature and density of the gas. This makes molecular clouds hard to understand without a good model to compare against. This is particularly true of modern telescopes as due to their improved resolution and sensitivity the observations are very complex due to the fine details that they can see. Consequently, the models from this project will be crucial in using ALMA and the SKA to determine how stars form throughout our Universe.