Institute for Advanced Study/Princeton University Joint Astrophysics Colloquium

It has been nearly 100 years since the "Great Debate," where Heber Curtis correctly argued that Thomas Wright's 1750 ideas about our Milky Way being one of many "galaxies," each a flattish disk of a multitude of stars, was correct. Since then, astronomers have made sharper and sharper images of galaxies beyond our own, often revealing intricate sprial structure. But, for the mostpart, our potentially super-close-up view of our own Galaxy's structure has been ruined by our unfortunate vantage point within its disk. Work over the past century indicates that the Milky Way is a barred spiral, but even the Galaxy's number of arms is still at-issue. In this talk, I will discuss how four techniques are being combined to tease out the true structure of the Milky Way. In particular, our collaboration* is combining 3D-dust mapping, searches for extraordinarily long galactic filaments called "Bones," position-position-velocity observations of gas, and numerical simulations to create a new, and sometimes very surprising, view of our Galaxy. Unexpected results to be presented include: several-hundred-pc long, ~1-pc wide, gaseous "Bones" lying in, and likely defining, the gravitational mid-plane of the Milky Way; a 2.5 kpc-long damped sine wave with 200-pc amplitude that seems to be the Local Arm (and the undoing of "Gould's Belt"); and simulations that suggest the need for feedback and/or magnetic fields, and/or stranger physics (dark matter in the disk?) in order to explain the Bones and/or the Local Arm's Wave.