The Gaia satellite has measured proper motions (meaning the motion across the sky) for more than a billion stars across the Galaxy. However, unfortunately for most of these stars we do not have the distances we need to turn these proper motions into velocities. RR Lyrae are a type of variable star where we can estimate accurate distances. We have therefore used a sample of almost 16,000 RR Lyrae measured by Gaia to measure the dynamics of the stars which make up the Milky Way's stellar halo.
Christopher Wegg, Ortwin Gerhard and Marie Bieth, 2019, MNRAS, 485, 3296