Theoretical Studies in Star Formation

麦基博士和他的团队研究恒星的形成及其历史，以研究控制宇宙演化的过程。恒星的形成历史决定了星系的结构和演化，以及随着时间的推移化学元素的产生。这项工作解决了恒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，如果磁场太强，恒星就无法摆脱磁场的影响。该小组使用一个数值磁辐射流体动力学自适应网格细化代码来模拟磁场对恒星形成的影响。巨大分子云中的大规模恒星形成受到这些云中磁场形状的影响。观测结果支持两种假设，即磁场要么是有序的，要么是混乱的。详细的模拟将与观测结果进行比较，以解决这个问题。在中等尺度上，星团形成过程影响恒星形成速率和恒星质量。包括辐射和从磁化介质中形成的原恒星流出物的影响的模拟将提供星团中恒星形成的更完整的画面。在更小的尺度上，磁场可以有效地提取正在形成和新近形成的恒星周围的圆盘中气体的旋转能量。迄今为止，大多数恒星形成模拟的结果要么是根本没有圆盘，要么是圆盘比观测到的要小得多。这里进行了高分辨率模拟，模拟了将气体与磁场耦合的所有相关物理过程，以解决这个问题。(2)宇宙时间内恒星形成的速率。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度以及这些气体转化为恒星的速度。气体的吸积是由大规模的宇宙学模拟确定的。PI对恒星形成速率的两个互补理论的发展做出了贡献。这些理论将被统一，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组成部分。第一批恒星的形成。最初的恒星是由气体形成的，基本上没有比氦更重的元素。当这些恒星在生命的尽头爆炸时，它们为宇宙播下了第一批重元素。产生的重元素的数量敏感地取决于这些恒星的质量。这个质量很可能受到恒星形成时发出的高能辐射的影响，这将在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而开发的计算方法将被公布供社区使用。

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.