A Programme in Astrophysical Theory and Observations at Leeds

这项研究计划主要研究恒星和行星是如何由尘埃和气体云形成的。恒星是由占据星际空间的气体云和混合在其中的微小尘埃颗粒形成的。这些云是高度丝状的，磁场也弥漫在太空中，很可能对它们的形成起到了作用，并控制它们在重力下坍塌形成恒星。我们将进行计算机模拟，以确定像我们的太阳这样的恒星是如何形成的。事实证明，比太阳质量大得多的恒星的形成问题要大得多，因为它们很稀有，距离很远，会产生惊人的辐射，将物质吹走，而不是让它掉进去。当流入的物质接近恒星时，我们预计它将在围绕恒星运行的薄薄圆盘中完成其旅程。用ALMA望远镜对分子发射的详细测绘开始揭示这些圆盘。我们将大大扩展这些最初的发现，并用复杂的模型解释数据，以找出材料是如何流入这些圆盘的。这些波长的分子所产生的丰富光谱将用新的数据挖掘技术来探索，以寻找我们可以追踪这些恒星形成时随时间变化的方法。将使用红外干涉测量技术研究这些圆盘的内部区域，在这些区域中，物质将完成其到达正在形成的恒星的旅程。这揭示了比哈勃太空望远镜好10到100倍的空间信息，在哈勃太空望远镜中，我们可能会开始看到材料被磁场引导。与此同时，这种物质通过圆盘螺旋状地飞向恒星，其中一些物质沿着旋转轴以高速抛射，同样很可能是通过磁场。为了进一步追踪这些喷气式飞机，我们将使用英国高度敏感的无线电天线网络e-Merlin来绘制它们的发射地图。与复杂模型的比较将显示粒子是否在这些喷流中被加速到相对论速度，进一步增强了它们对环境的潜在影响。随着大质量恒星最终开始清除它们出生的物质，由它们的强辐射场驱动的风的综合效应产生了戏剧性的影响。正如NASA的钱德拉卫星所观察到的那样，当风猛烈撞击分子材料并相互作用时，它们被加热到数百万度，并在X射线区域强烈发射。最大质量的恒星寿命如此之短，只有几百万年，它们可以作为超新星爆炸，同时仍然被分子云的残余物包围。计算机模拟将被用来解决这个问题，以研究这些过程如何终止巨型分子云中的恒星形成过程。像太阳这样正在形成的恒星周围的圆盘是行星形成的地点，这些行星是由尘埃颗粒聚合而成的。这被认为只发生在圆盘较安静的区域，那里磁场引起的湍流不那么强烈。我们将对冰粒升华时产生的化学效应进行计算，然后影响它们的电荷，从而影响它们的磁性。带电尘埃颗粒相对于气体的运动方式在形成过程中很重要，这一点将通过复杂的计算机模拟进行检验。在恒星寿命接近尾声的时候，开始行星形成过程的尘埃颗粒本身就会产生。我们将进行详细的化学计算，以找出这些硅酸盐矿物是如何从巨星丰富、凉爽的大气中的气体元素中形成的。其中许多较重的元素本身首先是在被称为超新星的爆炸恒星中产生的。我们将对这些恒星的热核爆进行最先进的模拟，并研究这如何影响宇宙中元素的产生。

This research programme principally addresses how stars and planets form from clouds of dust and gas.Stars form from the clouds of gas that occupy interstellar space and the small dust grains mixed in them. The clouds are highly filamentary and magnetic fields, that also pervade space, are likely to have had a role in shaping them, and controlling their collapse under gravity to form stars. We will conduct computer simulations to ascertain how the beginning of the formation of stars like our Sun takes place. The formation of stars much more massive than our Sun has proved to be much more problematic 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 is beginning to reveal these discs. We will significantly extend these initial discoveries and interpret the data with sophisticated models to find out how material flows into these discs. The rich spectra due to molecules at these wavelengths will be explored with novel data mining techniques to search for ways that we can trace changes over time as these stars form. The inner regions of these discs where the material completes its journey on to the forming star will be studied using the techniques of infrared interferometry. This reveals spatial information at levels 10 to 100 times better than the Hubble Space Telescope, where we may start to see the material being channelled by magnetic fields instead. 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, again most likely by magnetic fields. To follow these jets further out we will use the highly sensitive network of radio dishes in the UK, e-MERLIN, to map their emission. Comparison with complex models will show whether particles are being accelerated to relativistic speeds in these jets, further enhancing their potential impact on their environment.As massive stars finally begin to clear away the material from which they were born the combined effect of the winds driven by their strong radiation fields has a dramatic effect. As the winds slam into the molecular material and each other they get heated to millions of degrees and emit strongly in the X-ray region as observed with NASA's Chandra satellite. The most massive stars have such short lives of a few million years that they can blow up as supernovae whilst still surrounded by the remnants of the molecular clouds. Computer simulations will be used to tackle this problem to investigate how these processes can terminate the star formation episodes in giant molecular clouds. 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. This is only thought to occur in the quieter regions of the disc where turbulence due to the magnetic fields is less strong. We will perform calculations of the chemical effects that occur where the icy grains are sublimated that then affect their charge, and hence, magnetic properties. How the charged dust particles move relative to the gas is important in the formation process and that will be examined with sophisticated computer simulations. 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. Many of these heavier elements themselves are first made in the exploding stars known as supernovae. We will perform state-of-the-art simulations of the thermo-nuclear detonation of these stars, and examine how this affects the production of elements in the cosmos.