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.