Gaia & the fingerprints of the Galactic bar – A dynamical Milky Way mystery

Wilma Trick (MPA)

July 08, 2021

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Abstract: The Milky Way’s disk around the Sun is interspersed by 7 streams of stars, amongst them the famous Hercules, Sirius, and Hyades moving groups. These streaming motions are caused by some powerful perturber. Suspects are the spiral arms, satellites, and/or the Galactic bar. So far, the true culprit has been notoriously elusive. This talk shows how stars whose orbits are in resonance with the Galactic bar exhibit distinctive patterns in action-angle space. Based on these fingerprints, the exquisite Gaia data narrows down the search for the bar’s Outer Lindblad Resonance (OLR) to two likely candidates: the “Hat” and the “Sirius” moving groups. Finally pinning down the true OLR (and therefore the pattern speed of the Galactic bar) will be a milestone in uncovering the Milky Way’s structure and evolution.