Understanding the Role of Magnetic Fields in Star and Planet Formation Using Stratospheric Balloon-borne Polarimeters

恒星是由大量的分子气体云形成的。然而，这个过程的效率低得令人难以置信，因为分子云中最多有百分之几的气体最终会进入恒星。是什么导致这种低效是天体物理学中一个关键的悬而未决的问题。要回答这个问题，需要了解调节恒星形成的物理过程：重力、湍流气体运动、年轻恒星的反馈和磁场。在这些过程中，磁场是最难观察到的，因此也是最不了解的。我建议利用我们新的平流层气球偏振仪BLAST-TNG的观测，在从分子云复合体到单个原恒星和原行星盘的范围内，定量确定磁场在恒星形成中的作用。BLAST-TNG测量的是尘埃颗粒相对于其局部磁场对齐的亚毫米偏振光。地球大气层吸收了大部分亚毫米级的光，因此，通过在99.5%的大气层上方运行，BLAST-TNG可以以前所未有的详细程度绘制恒星形成区域的磁场。我们的研究将集中在三个主题上，每个主题由一名硕士/博士生领导：1)分子云中的磁场如何影响恒星形成的效率？之前的研究表明，磁场通常足够强，足以阻止气体穿过磁力线，这应该会减缓密度高、重力不稳定的气体的形成。我们将把我们的BLAST-TNG地图与恒星形成区域的模拟地图进行比较，以确定哪些云被强烈磁化，以及这些云是否在形成恒星方面效率较低。2)磁场是否支持细丝抵抗引力崩塌？密集的细丝似乎是恒星形成的首选地点。使用数百个细丝的BLAST-TNG图，以及使用高分辨率Toltec旋光仪的7个细丝的详细地图，我们将测试磁场是否支持细丝抵御引力坍塌。3)磁场是否抑制原行星盘的形成？圆盘的形成是崩塌核心角动量守恒的结果，但磁场可能会降低核心角动量，抑制圆盘形成。利用BLAST-TNG和Toltec，我们将研究数百颗原恒星的磁场，以确定轴与磁场对齐的圆盘是否更小，并研究磁场如何影响核心塌缩。这项研究将首次对磁场调节恒星形成效率和行星形成的程度进行定量测量。共有9名学生(3名硕士/博士，6名本科生)将获得分析大数据集的技能，参与大型国际合作，并展示他们的研究成果。我们的计划还将产生重要的公共遗产数据集，并进一步提高加拿大在恒星形成研究中的领先地位。

Stars form out of large clouds of molecular gas. However, this process is incredibly inefficient, in that typically at most a few percent of the gas in molecular clouds will end up in stars. What causes this inefficiency is a key outstanding question in astrophysics. To answer this question requires understanding the physical processes that regulate star formation: gravity, turbulent gas motions, feedback from young stars, and magnetic fields. Of these processes magnetic fields are the hardest to observe, and therefore the least understood. I propose to quantitatively determine the role of magnetic fields in star formation, over scales ranging from molecular cloud complexes to individual protostars and protoplanetary disks, using observations from our new stratospheric balloon-borne polarimeter BLAST-TNG. BLAST-TNG measures sub-mm polarized light radiated from dust grains aligned relative to their local magnetic field. The Earth's atmosphere absorbs most sub-mm light, so by operating above >99.5% of the atmosphere BLAST-TNG can map magnetic fields in star-forming regions with an unprecedented level of detail. Our research will focus on three topics, each led by an MSc/PhD student: 1)How do magnetic fields in molecular clouds affect the efficiency of star formation? Previous research shows that magnetic fields are generally strong enough to prevent gas from moving across field lines, which should slow down the formation of dense, gravitationally-unstable gas. We will compare our BLAST-TNG maps to maps made from simulations of star forming regions, to determine which clouds are strongly magnetized and whether these clouds are less efficient at forming stars. 2)Do magnetic fields support filaments against gravitational collapse? Dense filaments appear to be preferred sites of star formation. Using BLAST-TNG maps of hundreds of filaments, and detailed maps of seven filaments with the high resolution TolTEC polarimeter, we will test whether magnetic fields support filaments against gravitational collapse. 3)Do magnetic fields inhibit the formation of protoplanetary disks? Disks form as a consequence of angular momentum conservation in collapsing cores, but magnetic fields may reduce core angular momentum and inhibit disk formation. With BLAST-TNG and TolTEC we will study the magnetic fields of hundreds of protostars to determine whether disks with axes aligned with the magnetic field are smaller, and study how magnetic fields affect core collapse. This research will provide the first quantitative measurements of the degree to which magnetic fields regulate star formation efficiency and planet formation. In total 9 students (3 MSc/PhD, 6 undergraduate) trained in this program will gain skills in analyzing big datasets, working as part of large international collaborations, and presenting their research results. Our program will also generate important public legacy datasets and further Canada's leadership in the study of star formation.