Clouds, Filaments, Fields

Presentation Date: Tuesday, May 24, 2016. Location: Crutcher/Heiles Conference, Madison, WI. Abstract: Once, the space between the stars was thought to be empty. But, by the early 20th century, it became clear there was stuff in-between, thanks to obscuration caused by interstellar dust and absorption caused by interstellar gas. Maybe if astronomers had looked more carefully at Barnard’s images from the early 1900s, they never would have arranged the interstellar medium into “clouds,” but they did. By the 1970’s, after the detection of CO, “molecular clouds” became the places where stars formed, and “atomic clouds” were host to molecular clouds. Today’s trendy shape is “filaments,” because higher-and-higher resolution observations of the dusty, atomic, and molecular interstellar medium reveal networks of filaments--much like many of Barnard’s images did 100 years ago. In this talk, I will discuss how, and why, our view of the ISM’s topology has evolved, and I will consider which physical mechanisms collect and shape gas and dust most effectively. I will conclude with some currently puzzling results showing: tiny fibers in the atomic gas; twisted “fibers” in the molecular gas; and gigantically long “Bone-like” filaments that may trace out the Milky Way’s structure. And, just for Carl and Dick, I’ll try to use what we know from simulations to say something useful about the potential role of magnetic fields in shaping these extreme structures.

报告基本信息：举办日期为2016年5月24日（星期二）；举办地点为美国威斯康星州麦迪逊市的克拉彻/海尔斯学术会议（Crutcher/Heiles Conference）。
摘要：长久以来，恒星之间的星际空间曾被认为是真空无物的。但到20世纪早期，得益于星际尘埃引发的消光效应与星际气体造成的吸收效应，学界逐渐确认星际空间中存在物质。倘若天文学家当初更细致地审视巴纳德在20世纪初拍摄的天文影像，或许根本不会将星际介质划分为“云团”——但他们终究还是做出了这样的分类。到20世纪70年代，随着一氧化碳（CO）被探测到，“分子云”被认定为恒星形成的核心场所，而“原子云”则成为分子云的宿主环境。如今学界的研究热点转向纤维状结构：对含尘、原子及分子星际介质的观测分辨率不断提升，所得到的观测结果揭示出纤维状结构网络——这与巴纳德在100年前拍摄的诸多影像所呈现的特征高度相似。
在本次报告中，笔者将探讨学界对星际介质（Interstellar Medium, ISM）拓扑结构的认知是如何演变、因何演变，并分析哪些物理机制能够最高效地聚集并塑造气体与尘埃。报告的最后，笔者将展示几项当前仍存困惑的研究结果：原子气体中的细微纤维结构、分子气体中扭曲的“纤维”结构，以及可能勾勒出银河系整体结构的超长“骨状”纤维结构。此外，为致敬卡尔与迪克，笔者将尝试结合数值模拟所得的结论，阐释磁场在塑造这类极端结构中可能发挥的作用。