Theoretical Studies in Star Formation

恒星形成的理论研究

• 批准号: 1211729
• 负责人: Christopher McKee
• 金额: $ 49.23万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-01 至 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1211729&HistoricalAwards=false
• 关键词: Theoretical; Studies; Star; Formation

Dr. McKee and his group investigate star formation and its history to study the processes governing the evolution of the universe. The star formation history determines the structure and evolution of galaxies, and the production of the chemical elements over time. This work addresses three central problems in the theory of star formation. (1) The role of magnetic fields in the formation of low-mass stars. Magnetic fields affect their formation as stars cannot from if the field is too strong. The group uses a numerical magneto-radiative hydrodynamic - adaptive mesh refinement code to simulate the effects of magnetic fields on star formation. Large scale star formation in giant molecular clouds is affected by the shape of the magnetic field in these clouds. Observations support both hypotheses that either the field is ordered or tangled. Detailed simulations will be compared to observations to resolve this issue. On intermediate scales, processes during star cluster formation influences the star formation rates and the stellar masses. Simulations that include the effects of radiation and outflows from protostars forming out of a magnetized medium will provide a more complete picture of star formation in clusters. One smaller scales, magnetic fields are effective at extracting the rotational energy of the gas in disks that have been observed around forming and recently formed stars. Most star formation simulations to date result in either no disks at all, or in disks that are much smaller than observed. Here high resolution simulations with all relevant physical processes that couple the gas to the magnetic field are carried out to address this issue.(2) The rate of star formation through cosmic time. The evolution of disk galaxies like the Milky Way depends on the rate at which gas accretes onto the galaxy and the rate at which this gas is transformed into stars. Gas accretion has been determined by large scale cosmological simulations. The PI has contributed to the development of two complementary theories of the star formation rate. These theories will be unified and, with simulations, extended to the case when heavy element abundances were low in the early universe. The results can serve as ingredients for more accurate theories of the evolution of galaxies.(3) The formation of the first stars. The very first stars formed out of gas that had essentially no elements heavier than Helium. When these stars exploded at the end of their lives, they seeded the universe with the first heavy elements. The amount of heavy elements produced depends sensitively on the mass of these stars. This mass was likely affected by of the energetic radiation emitted by the stars as they formed, which will be studied in the highest resolution simulations yet performed in order to determine the mass of the first stars.This award supports a postdoctoral researcher. The computational methodologies developed as part of this project will be published for use by the community.

麦基博士和他的小组调查星星的形成和它的历史，研究宇宙演化的过程。星星的形成历史决定了星系的结构和演化，以及化学元素随时间的产生。这项工作解决了星星形成理论中的三个中心问题。(1)磁场在低质量恒星形成中的作用。磁场会影响它们的形成，因为如果磁场太强，恒星就无法形成。该小组使用一个数字磁辐射流体动力学自适应网格细化代码来模拟磁场对星星形成的影响。在巨大的分子云中形成大规模的星星受到这些云中磁场形状的影响。观测结果支持这两种假设，即场是有序的或纠缠的。将详细模拟与观察结果进行比较，以解决此问题。在中等尺度上，星星团形成过程影响着星星的形成速率和恒星质量。模拟包括辐射和流出的影响，从原恒星形成的磁化介质将提供一个更完整的图片星星形成的集群。在较小的尺度上，磁场可以有效地提取正在形成和最近形成的恒星周围观察到的圆盘中气体的旋转能量。迄今为止，大多数星星形成的模拟结果要么根本没有圆盘，要么圆盘比观察到的要小得多。在这里，进行了将气体耦合到磁场的所有相关物理过程的高分辨率模拟，以解决这个问题。(2)宇宙时间中星星形成的速率。像银河系这样的盘状星系的演化取决于气体吸积到星系上的速率以及这些气体转化为恒星的速率。气体吸积已经通过大尺度宇宙学模拟确定。PI为星星形成率的两个互补理论的发展做出了贡献。这些理论将被统一起来，并通过模拟扩展到早期宇宙中重元素丰度较低的情况。这些结果可以作为更精确的星系演化理论的成分。(3)第一批恒星的形成。最初的恒星是由气体形成的，基本上没有比氦重的元素。当这些恒星在生命的尽头爆炸时，它们为宇宙带来了第一批重元素。产生的重元素的数量敏感地取决于这些恒星的质量。这一质量可能受到恒星形成时发出的高能辐射的影响，这将在迄今为止最高分辨率的模拟中进行研究，以确定第一批恒星的质量。该奖项支持博士后研究人员。作为该项目的一部分开发的计算方法将出版供社区使用。