A Programme of Astrophysical Research at Leeds

这个研究项目主要研究恒星和行星是如何形成和演化的。恒星是由占据星际空间的气体云和混合在其中的小尘埃颗粒形成的。比我们的太阳质量大得多的恒星的形成被证明是更难以理解的，因为它们是罕见的和遥远的，并产生大量的辐射，吹走物质，而不是让它落入。当下落的物质接近星星时，我们预计它将在一个围绕星星旋转的薄圆盘中完成它的旅程。用阿尔马望远镜对分子发射的详细测绘将揭示这些圆盘是否稳定，或者它们是否会碎裂形成双星系统。这些圆盘的内部区域更热，将使用红外干涉测量和光谱学技术进行研究。这比哈勃太空望远镜显示的空间信息要好10到100倍。在物质通过圆盘螺旋式地落在星星上的同时，其中一些物质也在沿着旋转轴高速喷射，这很可能是由磁场驱动的。为了进一步跟踪这些喷流，我们将使用射电望远镜，包括英国的射电天线网络e-MERLIN，来绘制它们的发射。我们将寻找落在星星上的物质爆发与沿着喷流喷射的物质之间的联系。大多数恒星形成于星团中，但这种系统形成和演化的方式一直备受争议。来自欧空局盖亚卫星的新信息测量了恒星的精确距离和运动，将与分子气体云的其他数据一起用于与模拟进行比较。将开发新的统计技术来进行这种多维比较。在恒星形成的过程中，围绕着太阳这样的恒星的圆盘是行星形成的场所，是由尘埃颗粒聚结而成的。将对质量略大于太阳的恒星周围的这些圆盘的性质进行调查，以研究剩余气体被吹走和原行星之间的碰撞产生尘埃带的阶段。将用阿尔马望远镜对行星形成盘的化学组成进行高分辨率研究，以寻找行星形成和彗星形成外围的复杂有机分子。这些分子可能对生命的起源很重要。一项实验室研究将测量关键的化学反应速率，以找出生物系统途径上一些最有趣的分子是如何形成的。这些将被纳入光盘的化学模型，以解决生命起源的问题。围绕其他恒星的类地行星的可居住性将通过观察其宿主恒星的可变辐射输出对行星大气层损失的影响来研究。在恒星生命接近尾声时，行星形成过程开始的尘埃颗粒本身就产生了。我们将进行详细的化学计算，以弄清楚这些硅酸盐矿物是如何从巨大恒星的丰富，凉爽的大气中的气态元素中形成的。大质量恒星在演化过程中从表面吹出非常强劲的风，当它们处于双星系统中时，这些风会相互碰撞。这将带电粒子加速到接近光速，从而在无线电，X射线和伽马射线波段产生独特的发射，我们将模拟这些过程。当年轻恒星的喷流撞击周围的气体时，情况也类似。产生的快速粒子被称为宇宙射线，遍布银河系。在南非用MeerKAT射电望远镜对银河系进行的一项新的调查揭示了一个发射丝网络。我们将研究星际气体中的这种新现象及其与宇宙射线源的关系。

This research programme principally addresses how stars and planets form and evolve.Stars form from the clouds of gas that occupy interstellar space and the small dust grains mixed in them. The formation of stars much more massive than our Sun has proved to be much more difficult to understand as they are rare and distant and produce prodigious amounts of radiation that blow material away rather than let it fall in. As the infalling material gets close in to the star we expect it to complete its journey in a thin disc orbiting the star. Detailed mapping of the molecular emission with the ALMA telescope will reveal whether these discs are stable or whether they will fragment to form binary systems. The inner regions of these discs are hotter and will be studied using the techniques of infrared interferometry and spectroscopy. This reveals spatial information at levels 10 to 100 times better than the Hubble Space Telescope. At the same time that material is spiralling onto a star via a disc, some of it is being ejected at high speeds along the rotation axis, most likely driven by magnetic fields. To follow these jets further out we will use radio telescopes including the network of radio dishes in the UK, e-MERLIN, to map their emission. We will look for links between bursts of material falling on to the new star with ejections of material along the jets. Most stars form in clusters, but the way in which such systems form and evolve is hotly debated. New information from ESA's Gaia satellite that measures accurate distances and motions of stars will be used alongside other data on the molecular gas clouds to compare with simulations. Novel statistical techniques will be developed to undertake this multi-dimensional comparison. The discs that surround stars like the Sun as they are forming are the sites where planets form, built up from the coalescence of dust grains. A survey of the properties of these discs around stars slightly more massive than our Sun will be carried out to study the phase when the leftover gas is being blown away and collisions between proto-planets is creating belts of dust. A high resolution study of the chemical make up of planet forming discs will be carried out with the ALMA telescope to look for complex organic molecules in the planet-forming and comet-forming outer reaches. These molecules could be important in the origins of life. A laboratory study will measure key chemical reaction rates needed to find out how some of the most interesting molecules on the pathway to biological systems are formed. These will be incorporated in to chemical models of the discs to address questions on the origins of life. The habitability of Earth-like planets around other stars will be investigated by looking at the effect of their host stars variable output of radiation on the loss of the atmosphere of the planet.Near the end of the lives of stars, the very dust grains that begin the planet formation process are themselves produced. We will perform detailed chemical calculations to work out how these silicate minerals are built up from the gaseous elements in the rich, cool, atmospheres of giant stars. Massive stars blow very strong winds from their surfaces as they evolve and when they are in binaries these winds smash together. This accelarates charged particles up to close to the speed of light which generates distinctive emission in the radio, X-ray and gamma ray wavebands, which we will simulate to understand these processes. A similar situation pertains when the jets from young stars hit the surrounding gas. The fast particles produced are called cosmic rays and pervade the Galaxy. A new survey of our Milky Way with the MeerKAT radio elescope in South Africa has revealed a network of filaments of emission. We will investigate this new phenomena in the interstellar gas and its relationship to sources of cosmic rays.