The role of massive protoplanetary discs in the formation of stars and planets

巨大的原行星盘在恒星和行星形成中的作用

• 批准号: ST/H002308/1
• 负责人: William Rice
• 金额: $ 43.71万
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FH002308%2F1
• 关键词: role; massive; protoplanetary; discs; formation

It is now well known that stars form inside Giant Molecular Clouds (GMCs) made up primarily of cold, dense molecular hydrogen and dust. Although the molecular cloud cores from which stars form rotate very slowly, they still contain far more angular momentum than any single star. It is now well understood that most of the mass that ultimately forms a star - in particular low-mass stars - must first pass through a flattened circumstellar disc. What is still unknown is how the angular momentum is transported outwards through the disc, allowing mass to move inwards onto the star. Although, it has been suggested the magnetohydrodynamic (MHD) turbulence may provide a mechanism for transporting angular momentum, it seems unlikely that these discs are sufficiently ionised for this to operate effectively. Since most of the mass that forms the central star must first pass through the disc, it is quite likely that - comared to the mass of the central star - these discs may be relatively massive. This suggests that these discs could be susceptible to the growth of a gravitational instability which will lead to the formation of spiral density waves - a process analagous to the formation of spiral arms in disc galaxies. These spiral density waves act to transport angular momentum outwards allowing mass to accrete onto the central star. A primary goal of the work here will be to investigate - using analytic calculations and numerical simulations - the evolution of massive discs around young stars with the aim of understanding if this gravitational instability can be the primary transport mechanism in young stellar discs. In particular, these models will include detailed thermodynamics and radiation transfer as it is now clear that the evolution of the gravitationally instability depends strongly on the heating and cooling processes in the disc. If the gravitational instability is important, it is likely to be so during the earliest stages of star formation, which is also the period during which dust grains are expected to grow to form planetesimals - the building blocks of planets. One aspect of the planet formation process that is still not understood is how cm-sized particles grow quickly into kilometre-sized bodies. It has already been suggested that spitral density waves may play a role in planet formation by producing dense collections of particles that can either grow rapidly through collisions or could grow directly through gravitational collapse. Together with studying the evolution of gravitationally unstable discs we will also investigate if the resulting spiral density waves can play a role in the formation of planetesimals. This will extend earlier work in that we will have a detailed understanding of where spiral waves are likely to exist in protostellar discs and how strong they are likely to be. We will also aim to quantify the influence of spiral density waves on the population of cm-sized grains to see if their subsequent growth occurs through collisions or if they can become sufficiently dense to grow through direct gravitational collapse.

现在众所周知，恒星形成于巨分子云（Giant Molecular Clouds，GMC）内部，主要由寒冷、致密的分子氢和尘埃组成。虽然形成恒星的分子云核心旋转得非常慢，但它们仍然比任何单个星星包含更多的角动量。现在已经很清楚，最终形成星星的大部分物质--特别是低质量恒星--必须首先通过一个扁平的星周盘。目前尚不清楚的是，角动量是如何通过圆盘向外传输的，从而使质量向内移动到星星上。虽然，它已被建议的磁流体动力学（MHD）湍流可以提供一种机制，用于传输角动量，似乎不太可能，这些光盘是足够的电离，这有效地运作。由于形成中心星星的大部分质量必须首先通过圆盘，因此与中心星星的质量相比，这些圆盘很可能相对较大。这表明这些盘可能容易受到引力不稳定性的增长，这将导致螺旋密度波的形成-这一过程类似于盘星系中螺旋臂的形成。这些螺旋密度波的作用是向外输送角动量，使质量能够在中心星星上增加。这项工作的主要目标是研究-使用分析计算和数值模拟-年轻恒星周围大质量盘的演化，目的是了解这种引力不稳定性是否可以成为年轻恒星盘的主要传输机制。特别是，这些模型将包括详细的热力学和辐射传输，因为现在很清楚，引力不稳定性的演变强烈依赖于盘中的加热和冷却过程。如果说引力不稳定性很重要，那么在星星形成的最早阶段就很可能如此，这一阶段也是尘埃颗粒生长形成星子的时期--星子是行星的基石。行星形成过程中仍不清楚的一个方面是厘米大小的颗粒如何快速生长成公里大小的物体。已经有人提出，螺旋密度波可能在行星形成中发挥作用，产生密集的粒子集合，这些粒子可以通过碰撞快速增长，也可以通过引力坍缩直接增长。在研究引力不稳定盘的演化的同时，我们还将研究由此产生的螺旋密度波是否能在微行星的形成中发挥作用。这将扩展早期的工作，因为我们将详细了解螺旋波可能存在于原恒星盘中的位置以及它们可能有多强。我们还将量化螺旋密度波对厘米级颗粒群的影响，以确定它们随后的生长是否通过碰撞发生，或者它们是否可以通过直接引力坍缩变得足够致密。