What Controls Star Formation in Galaxies?

本研究评估了分子云和恒星形成过程中不同物理过程的相对重要性。总的来说，这提高了我们对分子云形成动力学的理解，以及外部流和内部大质量恒星形成如何再次驱散或摧毁它们。它测试恒星的形成速率是否受分子云形成的控制，这是由于圆盘中部的高压造成的，还是由气体和恒星结合的引力不稳定造成的。相关的问题是分子云的寿命和恒星形成效率。Mac Low博士和他的团队使用FLASH自适应网格细化（AMR）模拟代码，可以处理对恒星形成模型至关重要的最重要的物理过程的建模。其中包括超新星爆炸的影响；自我引力;剪切片近似中的微分旋转；来自点源的电离、解离和非电离但加热的辐射；磁场;分子化学的两个不同近似水平；在光学薄区和光学厚区近似辐射冷却；维持垂直分层的固定的恒星引力势；银河喷泉；同时释放辐射和恒星喷流和风的粒子。这些模型的建立是为了将影响整合到恒星形成的多尺度模型中，该模型涵盖了从0.5千秒差距到100天文单位的尺度。这些结果有助于区分“高中间压力”模型和“重力不稳定”模型。因此，自一致的数值模型遵循巨大分子云的组装和其中恒星形成的结果。研究小组通过参数研究来评估这些过程的相对重要性，使用这些模型的完全解析版本和完整的化学反应。这个研究项目是博物馆和海德堡大学理论天体物理研究所的一个国际合作项目。它还将支持研究生的培训。这项研究的结果也被纳入美国自然历史博物馆的展览和教育计划，包括海登天文馆。

This investigation evaluates the relative importance different physical processes during molecular cloud and star formation. Overall, this improves our understanding of the dynamics of molecular cloud formation and of how external flows and internal massive star formation act to disperse or destroy them again. It tests whether star formation rates are governed by molecular cloud formation due to high pressure in a disk's mid-plane, or by gravitational instability of the combination of gas and stars. Related problems are the lifetimes and star formation efficiency in molecular clouds. Dr. Mac Low and his team use the FLASH adaptive mesh refinement (AMR) simulation code that can handle the modeling of the most important physical processes important to star formation models. These include effects of supernova explosions; self gravity; differential rotation in the shearing sheet approximation; ionizing, dissociating, and non-ionizing but heating radiation from point sources; magnetic fields; molecular chemistry in two different levels of approximation; an approximation to radiative cooling in optically thin and thick regions; a fixed stellar gravitational potential to maintain vertical stratification; the full galactic fountain; and sink particles emitting both radiation and stellar jets and winds. The models are done so that effects are integrated into a multiscale model of star formation covering scales ranging from 0.5 kiloparsec down to 100 Astronomical Units. The results help to distinguish between the "high midplane pressure" and the "gravitational instability" models. Thus, self-consistent numerical models follow the assembly of giant molecular clouds and the results of star formation within them. The team evaluates the relative importance of these processes by parameter studies using the fully resolved version of these models with full chemistry.This research program is an international collaboration between the Museum and the Institute for Theoretical Astrophysics of the University of Heidelberg. It will also support the training of a graduate student. Results from this research are also incorporated into the exhibition and education program of the American Museum of Natural History, including the Hayden Planetarium.