ASTThe Formation and Dynamics of Star Clusters

天文学家目前面临的主要问题之一是"恒星是如何形成的？“我们自己的太阳是银河系130亿年生命中形成的数十亿颗恒星之一。当我们观察这些恒星时，我们看到了各种各样的大小，质量和温度。有些恒星看起来是孤立的，有些与另一颗星星生活在一个双星系统中，有些是在被称为星团的恒星群中发现的。我们认为大多数恒星形成于不同大小的星团中，但最近的观测对这一理论提出了质疑。通过研究这些群体，我们希望更好地了解恒星和星团如何形成我们所看到的各种属性，以及这如何影响这些恒星周围行星的形成，例如我们自己的地球。这是因为许多天体物理过程需要数千年才能发生，而且不可能从头到尾观察这些过程。虽然我们可以从一张快照中了解很多关于星星集群的信息（比如其中恒星的数量，它们的总质量和年龄），但缺少一个关键因素：恒星的运动。如果我们能够测量星团中的单个恒星是如何移动的，我们就可以用计算机模拟出几百万年前星团的样子，以及它在未来将如何继续发展。当我们想了解星星团的结构以及它们是在膨胀还是在坍缩时，这一点可能很重要。有两种方法可以测量星团中恒星的运动。为了测量向我们飞来的恒星的运动，我们使用星星发出的光谱，并测量光谱线位置的变化，这些光谱线根据称为多普勒效应的过程而移动。当消防车向你驶来，然后又离开你时，警笛的音调会发生变化，这和这个过程是一样的。为了测量恒星横向运动的速度，我们研究了相隔多年的星星的图像，以了解恒星如何相对于更静止的背景恒星运动。这是一项艰苦而细致的工作--在这些恒星的距离上，它们几公里/秒的横向速度相当于能够测量国际空间站上某人头发的生长速度，而你自己则站在地球表面!我的目标是利用这些测量结果，对许多不同的星星形成区域和星星集群中的数百颗年轻恒星进行测量，以了解这些区域是在膨胀还是在坍缩，以及是什么物理机制在驱动这些过程。这有点像在迪斯科舞厅，但听不到音乐。通过观察人们跳舞，可以知道正在播放的是哪首歌。对星星团来说也是如此：通过研究恒星的舞蹈，我们可以弄清楚是什么物理机制在起作用。这个领域让我兴奋的是，我们刚刚进入一个新的探索阶段的感觉。纵观整个天文学历史，绝大多数恒星和星系都是静止的，从不变化，从不运动。探测器技术和计算机科学的最新进展，加上多国对盖亚卫星和盖亚-ESO巡天等新设施的投资，将改变我们对天空的看法，并向我们展示天空如何随着时间的推移而变化。最后，我们正在克服我们的静态视图，可以看到星星的舞蹈第一次。对于像我这样的年轻研究人员来说，等待着新发现的宝库。我的项目将使我站在这个剥削新时代的最前沿。

One of the major questions astronomers currently face is "how do stars form?" Our own Sun is one of billions of stars that have formed in the 13-billion year lifetime of our Galaxy. When we look at these stars we see a wide range of sizes, masses and temperatures. Some stars appear isolated, others live in a binary system with another star, and some are found in groups of stars known as clusters. We think that the majority of stars form in clusters of various sizes, but recent observations have thrown doubt on this theory. By studying these groups we hope to better understand how stars and star clusters form with the wide range of properties that we see, and how this impacts the formation of planets around these stars, such as our own Earth.So far astronomers have relied upon information from a single snapshot in time to study star clusters. This is because many astrophysical processes take millennia to occur and it is impossible to observe these processes from start to finish. While we can learn a lot about star clusters from a single snapshot (such as the number of stars in them, their total mass and age) there is a critical ingredient missing: the motions of the stars. If we can measure how the individual stars in clusters are moving, we can work out using computer simulations what the cluster might have looked like a few million years ago, and how it will continue to develop in the future. This can be important when we want to understand the structure of star clusters and whether they are expanding or collapsing.There are two ways to measure the motions of stars in clusters. To measure the motions of stars coming towards us we use a spectrum of the light emitted by the star and measure the change in the position of spectral lines that shift according to a process known as the Doppler effect. This is the same process that changes the pitch of a siren when a fire engine travels towards you and then away from you. To measure the velocities of stars moving transversely we study images of the star separated by many years to see how the stars move relative to more stationary background stars. This is painstaking and detailed work - at the distances of these stars their transverse velocities of a few km/s are equivalent to being able to measure the rate of someone's hair growth on the International Space Station while you yourself are stood on the surface of the Earth!My goal is use these measurements for hundreds of young stars in many different star forming regions and star clusters to understand whether these regions are expanding or collapsing and what physical mechanisms are driving these processes. This is somewhat like being at a disco, but not being able to hear the music. By watching people dance it can be possible to work out what song is playing. The same is true for star clusters: by studying the dance of the stars we can work out what physical mechanisms are at work.What excites me about this area is the feeling that we are just now entering a new phase of exploration. Throughout the entire history of astronomy the vast majority of stars and galaxies have been static, never changing and never moving. Recent advances in detector technology and computer science combined with multi-national investment in new facilities such as the Gaia satellite and the Gaia-ESO Survey will transform our view of the sky and show us how the heavens change over time. At last we are overcoming our static view and can see the dance of the stars for the first time. For young researchers like myself, there awaits a treasure-trove of new discoveries. My project will put me at the forefront of this new era of exploitation.