Star Formation and Protoplanetary Discs

这个研究项目解决了恒星是如何从星系中的尘埃和气体云中形成的关键问题。我们还研究了为新恒星提供物质的旋转圆盘的工作过程：正是这些圆盘进化成行星。磁场遍布星际空间，并在控制物质如何积聚成密度越来越大的核心方面发挥着至关重要的作用，因为在坍缩成恒星-行星系统的过程中，引力占据了上风。尽管恒星诞生的地方寒冷而稠密，但仍有一些带电粒子，如电子、分子离子，更重要的是，还有带电的尘埃颗粒。我们将用计算机模拟研究带电尘埃颗粒的存在如何影响恒星和盘的形成。在观测上，我们将使用欧空局的新赫歇尔卫星来研究这些过程，该卫星将在许多分子发射的远红外区域提供第一个敏感光谱。这将与地面上运行在微波区域的望远镜阵列的分子发射的详细地图相结合，特别是智利的新ALMA望远镜，它有66个碟形天线串联工作。这些云团的化学成分，以及从它们发射线的蓝移和红移中获得的洞见，将使我们能够推断出是什么过程控制着恒星诞生的关键早期阶段。新的ALMA望远镜提供的高水平空间细节也将用于绘制比太阳大得多的恒星上的落入图。事实证明，它们的形成更有问题，因为它们稀少、遥远，而且会产生大量的辐射，把物质吹走，而不是让它们落进去。我们将研究一个大质量形成恒星的样本，这个样本在整个银河系中已经接近完成，这是我们用美国MSX卫星对银河系进行红外线调查后发现的。当物质靠近恒星时，我们预计它会以一个绕恒星运行的薄圆盘的形式完成它的旅程。我们将使用红外干涉测量的新技术系统地搜索我们的样本，该技术将来自VLT的两个或三个大型8米望远镜的光结合起来。此外，我们可以利用单架望远镜的高质量光谱来寻找来自圆盘相对于星光产生的线条的微小空间变化，从而获得比哈勃太空望远镜高10到100倍的空间信息。与此同时，这些物质通过圆盘旋转到恒星上，其中一些物质沿着旋转轴高速喷射出来。据认为，磁场是加速和引导物质进入这些喷流的原因。我们将使用英国高度敏感的新无线电天线网络——e-Merlin，来绘制这些喷流的发射图，并研究它们是如何进入周围的分子物质中，在云中吹出洞来的。无线电、微波和红外观测在大范围质量和进化阶段的结合将使我们能够解开工作中各种相互竞争的过程。当大质量恒星最终开始清除它们诞生的物质时，由它们强大的辐射场驱动的风的综合效应产生了戏剧性的影响。团块云被吹过密度较低区域的疾风撕碎。当它撞击分子物质时，它被加热到数百万度，并在x射线区域发出强烈的辐射，这是美国宇航局钱德拉卫星观测到的。相互碰撞的风也可以加速粒子并产生所谓的宇宙射线，我们应该在无线电和伽马射线波长上看到这一点的证据。计算机模拟将用于解决这个问题，以研究这些过程如何终止巨大分子云和其他星系中大质量恒星形成集中爆发的恒星形成事件。

This research programme addresses key questions on how stars form from clouds of dust and gas in galaxies. We also investigate processes at work in the swirling discs that feed material onto the new stars: the very discs that evolve to form planets. Magnetic fields pervade interstellar space and play a crucial role in controlling how material can accumulate into ever denser cores as gravity takes hold during the collapse to a star-planet system. Even though stellar birth sites are cold and dense there are still some charged particles such as electrons, molecular ions and, importantly, charged grains of dust. We will investigate with computer simulations how the presence of charged dust grains affects the formation of stars and discs. Observationally we will study these processes using ESA's new Herschel satellite which will provide the first sensitive spectrum in the far-infrared region where many molecules emit. This will be coupled with detailed mapping of molecular emission from the ground with arrays of telescopes operating in the microwave region, and especially the new ALMA telescope in Chile with 66 dishes working in tandem. The chemical composition of these clouds and the insight from the blue- and red- shifts of their emission lines will allow us to infer what processes are controlling these crucial early stages in the birth of stars. The high level of spatial detail afforded by the new ALMA telescope will also be used to map out the infall onto stars much more massive than our Sun. Their formation 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. We will study a sample of massive forming stars which is close to being complete across the whole Galaxy, that we have found from following up an infrared survey of our Galaxy with the American MSX satellite. As the material gets close in to the star we expect it to complete its journey in a thin disc orbiting the star. We will systematically search our sample for these discs using the new technique of infrared interferometry which combines the light from two or three of the large 8 m telescopes of the VLT. In addition, we can use very high quality spectra from single telescopes to look for tiny spatial shifts from lines that arise from the disc relative to the starlight to gain 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. It is thought that magnetic fields are responsible for accelerating and channelling material into these jets. We will use the highly sensitive new network of radio dishes in the UK, e-Merlin, to map the emission from these jets and study how these plough into the surrounding infalling molecular material to blow holes in the cloud. The combination of radio, microwave and infrared observations across a wide range of masses and stages of evolution will enable us to disentangle the various competing processes at work. 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. The clumpy cloud gets shredded by the fast wind whistling through the less dense regions. As it slams into the molecular material it gets heated to millions of degrees and emits strongly in the X-ray region as observed with NASA's Chandra satellite. The winds colliding with each other can also accelerate particles and produce the so-called cosmic rays and we should see evidence of this at radio and gamma ray wavelengths. Computer simulations will be used to tackle this problem to investigate how these processes can terminate the star formation episodes in giant molecular clouds and in other galaxies where concentrated bursts of massive star formation take place.